Separation bubbles forming on airfoils significantly influence aerodynamic behavior,particularly at low Reynolds numbers,making their accurate prediction a critical challenge in transition modelling.This study investi...Separation bubbles forming on airfoils significantly influence aerodynamic behavior,particularly at low Reynolds numbers,making their accurate prediction a critical challenge in transition modelling.This study investigates numerical modeling of a separation bubble and the effects of airfoil thickness and camber variation on the formation of the bubble dynamics at low Reynolds numbers.The numerical results were compared with the experimental results obtained from surface pressure distribution measurements,oil flow visualisation,and surface shear measurements to analyse the detailed flow behavior.The combination of pressure and flow visualisation techniques provided complementary insights,enabling a detailed characterisation of bubble formation.The results reveal that both the thickness and camber of the airfoil significantly influence the location,length,and stability of the bubble.At low Reynolds number flows(Re=0.5×10^(5)),particularly for highly cambered profiles,closer to the leading edge,separation and long bubbles were observed.As the Reynolds number increased,the separation point shifted to the leading edge,and reattachment became more likely.In numerical studies,transition models can accurately model the bubble initiation point;however,they often fail to model the bubble reattachment points accurately.This is due to the inadequacy of models that use empirical expressions for turbulence modelling,particularly in low Reynolds number flows,in their viscous modelling.In this study,it was concluded that transition onset terms,which specifically affect bubble formation,should be modified for more accurate modeling.展开更多
This work presents a simulation analysis using a multi-objective evolutionary algorithm for the thermo-hydraulic behavior of staggered heat sinks whose fins have NACA 0040 airfoil profile.The results were compared wit...This work presents a simulation analysis using a multi-objective evolutionary algorithm for the thermo-hydraulic behavior of staggered heat sinks whose fins have NACA 0040 airfoil profile.The results were compared with a conventional pin fin heat sink with a circular profile.This study searched for the best thermo-hydraulic performance by translational and rotational positioning of the fins.It is worth mentioning that this work was carried out in two stages.In the first stage,the thermo-hydraulic behavior of the heat sink was studied moving the location of the upper array above the X-axis from to 2.25 mm and above the Y-axis from to 1.275 mm.The second stage examined-2.25-1.55the effects of fin rotation considering the results found in stage 1.However,in this second stage,both arrays were free to rotate.For the upper array,the rotation range was-25°to 25° and for the lower array the rotation range was-15° to 15°.It is worth mentioning that both stages were analyzed for a single Reynolds(Re)number value of 13,000.The optimization results using the multi-objective evolutionary algorithm showed that compared to a NACA 0040 heat sink with fixed,unrotated original configuration(C0),the NACA 0040 heat sink with any Position Configuration(PC)did not significantly improve the heat transfer.Then,the results found in the second stage showed that the effect of the rotation of both sets did not influence the increase in pressure drop.However,it was found that with the Optimal Position and Rotation Configuration(PRCoptimal),which is the optimized array from Stage 1(position)then optimized by rotation,there is a slightly higher Performance Evaluation Criterion(PEC)compared to the original C0 configuration by 7%.Finally,the proposed NACA 0040 heat sink with the optimal rotation and position setting(PRCoptimal)was found to have a PEC of 9%compared to a conventional pin fin heat sink.展开更多
Recent advances in contrastive language-image pretraining(CLIP)models and generative AI have demonstrated significant capabilities in cross-modal understanding and content generation.Based on these developments,this s...Recent advances in contrastive language-image pretraining(CLIP)models and generative AI have demonstrated significant capabilities in cross-modal understanding and content generation.Based on these developments,this study introduces a novel framework for airfoil design via natural language interfaces.To the authors’knowledge,this study establishes the first end-to-end,bidirectional mapping between textual descriptions(e.g.,“low-drag supercritical wing for transonic conditions”)and parametric airfoil geometries represented by class-shape transformation parameters.The proposed approach integrates a CLIP-inspired architecture that aligns text embeddings with airfoil parameter spaces through contrastive learning,along with a semantically conditioned decoder that produces physically plausible airfoil geometries from latent representations.The experimental results validate the framework’s ability to generate aerodynamically plausible airfoils from natural language specifications and to classify airfoils accurately based on given textual labels.This research reduces the expertise threshold for preliminary airfoil design and highlights the potential for human-AI collaboration in aerospace engineering.展开更多
For a complex flow about multi-element airfoils a mixed grid method is set up. C-type grids are produced on each element′s body and in their wakes at first, O-type grids are given in the outmost area, and H-type grid...For a complex flow about multi-element airfoils a mixed grid method is set up. C-type grids are produced on each element′s body and in their wakes at first, O-type grids are given in the outmost area, and H-type grids are used in middle additional areas. An algebra method is used to produce the initial grids in each area. And the girds are optimized by elliptical differential equation method. Then C-O-H zonal patched grids around multi-element airfoils are produced automatically and efficiently. A time accurate finite-volume integration method is used to solve the compressible laminar and turbulent Navier-Stokes (N-S) equations on the grids. Computational results prove the method to be effective.展开更多
This paper examines a model that combines vortex generators and leading-edge tubercles for controlling the laminar separation bubble(LSB)over an airfoil at low Reynolds numbers(Re).This new concept of passive flow con...This paper examines a model that combines vortex generators and leading-edge tubercles for controlling the laminar separation bubble(LSB)over an airfoil at low Reynolds numbers(Re).This new concept of passive flow control technique utilizing a tubercle and vortex generator(VG)close to the leading edge was analyzed numerically for a NACA0015 airfoil.In this study,the Shear Stress Transport(SST)turbulence model was employed in the numerical modelling.Numerical modelling was completed using the ANSYS-Fluent 18.2 solver.Analyses were conducted to investigate the flow pattern and understand the underlying LSB control phenomena that enabled the new passive flow control method to provide this significant performance benefit.The findings indicated that the new concept of passive flow control technique suppressed the formation of an LSB at the suction surface of the NACA0015 airfoil,resulting in a higher lift coefficient and improved aerodynamic performance.Improvements in LSB dynamics and aerodynamic performance through the passive flow control method lead to increased energy output and enhanced stability.展开更多
This study investigates the aerodynamic efficacy enhancement of a NACA4412 airfoil using three-dimensional large eddy simulation analysis by integrating hybrid flow control techniques.The research focuses on the combi...This study investigates the aerodynamic efficacy enhancement of a NACA4412 airfoil using three-dimensional large eddy simulation analysis by integrating hybrid flow control techniques.The research focuses on the combined effects of cavity-based passive flow control and a dielectric barrier discharge plasma actuator aiming to increase lift and reduce drag particularly at higher Angles of Attack(AOA).Simulations were conducted at a Reynolds number of 3.1×10~6over an AOA range of 0°–20°.Four distinct cavity shapes,circular,rectangular,triangular,and curved rectangular,were analyzed,and the cavities were placed near the trailing edge on the pressure side while the plasma actuator was positioned at 2%of the chord length near the leading edge.The interaction between cavities and plasma actuation is found to mitigate flow separation by inducing vortex generation,which promotes smaller-scale vortex structures and narrows the wake.At lower AOA,cavities alone enhance lift by 20%to 30%while at higher AOA,the combination of cavities and plasma actuation achieves lift improvements of 94%to 106%.The combined system of the circular cavity and plasma actuator reduces drag at higher AOA by up to 27.56%which significantly enhances aerodynamic efficiency,and this combination yields the greatest lift to drag ratio.Vortex structure visualizations around the cavities reveal delayed flow separation and improved flow stability.Rectangular cavities alone show notable lift increases at lower AOA,and their combination with plasma actuation further reduces drag by up to 11%at higher AOA.This study demonstrates the efficacy of integrating passive and active flow control strategies for superior aerodynamic performance,highlighting their potential for highperformance airfoil applications at elevated angles of attack.展开更多
Although the thin and cold Martian atmosphere provides the feasibility of rotorcraft flight on Mars,rotors designed for denser Earth atmosphere with small angles of attack hardly generate enough thrust for rotorcraft ...Although the thin and cold Martian atmosphere provides the feasibility of rotorcraft flight on Mars,rotors designed for denser Earth atmosphere with small angles of attack hardly generate enough thrust for rotorcraft flight at conventional rotational speeds in the Martian atmosphere.In this paper,we employ the Particle Swarm Optimization(PSO)algorithm to search for the control points of the Bezier curve,completing the parameterization of the airfoil upper and lower curves based on these control points.In order to directly enhance the lift-to-drag ratio of the airfoil at high angles of attack,the NSGA-II algorithm is utilized to optimize the lift-to-drag ratio of NACA 6904 at a=17.5°,Ma=0.43,Re=7600,and CLF 5605 at a=15°,Ma=0.7,Re=7481,respectively.The two-dimensional RANS(Reynolds Average NavierStokes)and k-ωSST turbulence models are employed in the optimization process by CFD to predict the lift and drag characteristics of the airfoil in a Martian environment.Under simulated Mars atmospheric conditions(pressure of 1380 Pa,test temperature of 24°C,equivalent Mars atmospheric density at the surface of 0.0162 g/cm~3),the airfoil after optimized is subjected to rotor lift-drag characteristic tests where a single-rotor lift-drag characteristic test bench is employed for verification.The experimental results demonstrate that the RB-TB-II blade,which is obtained by optimizing the airfoil based on the RB-SWQ-I blade,exhibits a 19.6%increase in Power Loading(PL)and a 20.4%increase in Figure of Merit(FM)compared with the RB-SWQ-I blade.Based on the results of airfoil optimization,increasing the camber at the leading edge of the airfoil under high angles of attack contributes to an improved lift-to-drag ratio.展开更多
Aerodynamic force and flow structures of two airfoils in a tandem configuration in flapping motions axe studied, by solving the Navier-Stokes equations in moving overset grids. Three typical phase differences between ...Aerodynamic force and flow structures of two airfoils in a tandem configuration in flapping motions axe studied, by solving the Navier-Stokes equations in moving overset grids. Three typical phase differences between the fore- and aft-airfoil flapping cycles are considered. It is shown that: (1) in the case of no interaction (single airfoil), the time average of the vertical force coefficient over the downstroke is 2.74, which is about 3 times as large as the maximum steady-state lift coefficient of a dragonfly wing; the time average of the horizontal force coefficient is 1.97, which is also large. The reasons for the large force coefficients are the acceleration at the beginning of a stroke, the delayed stall and the 'pitching-up' motion near the end of the stroke. (2) In the cases of two-airfoils, the time-variations of the force and moment coefficients on each airfoil are broadly similar to that of the single airfoil in that the vertical force is mainly produced in downstroke and the horizontal force in upstroke, but very large differences exist due to the interaction. (3) For in-phase stroking, the major differences caused by the interaction are that the vertical force on FA in downstroke is increased and the horizontal force on FA in upstroke decreased. As a result, the magnitude of the resultant force is almost unchanged but it inclines less forward. (4) For counter stroking, the major differences are that the vertical force on AA in downstroke and the horizontal force on FA in upstroke are decreased. As a result, the magnitude of the resultant force is decreased by about 20 percent but its direction is almost unchanged. (5) For 90 degrees -phase-difference stroking, the major differences axe that the vertical force on AA in downstroke and the horizontal force on FA in upstroke axe decreased greatly and the horizontal force on AA in upstroke increased. As a result, the magnitude of the resultant force is decreased by about 28% and it inclines more forward. (6) Among the three cases of phase angles, inphase flapping produces the largest vertical force (also the largest resultant force); the 90 degrees -phase-difference flapping results in the largest horizontal force, but the smallest resultant force.展开更多
A robust optimization design approach of natural laminar airfoils is developed in this paper. First, the non-uniform rational B-splines （NURBS） free form deformation method based on NURBS basis function is introduce...A robust optimization design approach of natural laminar airfoils is developed in this paper. First, the non-uniform rational B-splines （NURBS） free form deformation method based on NURBS basis function is introduced to the airfoil parameterization. Second, aerodynamic characteristics are evaluated by solving Navier-Stokes equations, and theγ-Reθt transition model coupling with shear-stress transport （SST） turbulent model is introduced to simulate boundary layer transition. A numerical simulation of transition flow around NLF0416 airfoil is conducted to test the code. The comparison between numerical simulation results and wind tunnel test data approves the validity and applicability of the present transition model. Third, the optimization system is set up, which uses the separated particle swarm optimization （SPSO） as search algorithm and combines the Kriging models as surrogate model during optimization. The system is applied to carry out robust design about the uncertainty of lift coefficient and Mach number for NASA NLF-0115 airfoil. The data of optimized airfoil aerodynamic characteristics indicates that the optimized airfoil can maintain laminar flow stably in an uncertain range and has a wider range of low drag.展开更多
Natural ice accretion on the lifting surface of an aircraft is detrimental to its aerodynamic performance, as it changes the effective streamlined body. The main focus of this work considers the optimization design of...Natural ice accretion on the lifting surface of an aircraft is detrimental to its aerodynamic performance, as it changes the effective streamlined body. The main focus of this work considers the optimization design of airfoils under atmospheric icing conditions for the Unmanned Aerial Vehicle(UAV). The ice formation process is simulated by the Eulerian approach and the three-dimensional Myers model. A three-equation turbulence model is implemented to accurately predict the stall performance of the iced airfoil. In recognition of the real atmospheric variability in the icing parameters, the medium volume diameter of supercooled water droplets is treated as an uncertainty with an assumed probability density function. A technique of polynomial chaos expansion is used to propagate the input uncertainty through the deterministic system. The numerical results show that the multipoint/multiobjective optimization strategy can efficiently improve both the ice tolerance and the cruise performance of an airfoil. The reason for the focus on robust optimization is that the ice angle of the optimized airfoil becomes less critical to the incoming flow.The optimized airfoils are applied to a UAV platform, in which the performance improvement and the relevant key flow feature are both preserved.展开更多
Introducing active flow control into the design of flapping wing is an effective way to enhance its aerodynamic performance.In this paper,a novel active flow control technology called Co-Flow Jet(CFJ)is applied to fla...Introducing active flow control into the design of flapping wing is an effective way to enhance its aerodynamic performance.In this paper,a novel active flow control technology called Co-Flow Jet(CFJ)is applied to flapping airfoils.The effect of CFJ on aerodynamic performance of flapping airfoils at low Reynolds number is numerically investigated using Unsteady Reynolds Averaged Navier-Stokes(URANS)simulation with Spalart-Allmaras(SA)turbulence model.Numerical methods are validated by a NACA6415-based CFJ airfoil case and a S809 pitching airfoil case.Then NACA6415 baseline airfoil and NACA6415-based CFJ airfoil with jet-off and jet-on are simulated in flapping motion,with Reynolds number 70,000 and reduced frequency 0.2.As a result,CFJ airfoils with jet-on generally have better lift and thrust characteristics than baseline airfoils and jet-off airfoil when Cμgreater than 0.04,which results from the CFJ effect of reducing flow separation by injecting high-energy fluid into boundary layer.Besides,typical kinematic and geometric parameters,including the reduced frequency and the positions of the suction and injection slot,are systematically studied to figure out their influence on aerodynamic performance of the CFJ airfoil.And a variable Cμjet control strategy is proposed to further improve effective propulsive efficiency.Compared with using constant Cμ,an increase of effective propulsive efficiency by22.6%has been achieved by using prescribed variable CμNACA6415-based CFJ airfoil at frequency 0.2.This study may provide some guidance to performance enhancement for Flapping wing Micro Air Vehicles(FMAV).展开更多
This article presents a novel approach for predicting transition locations over airfoils,which are used to activate turbulence model in a Reynolds-averaged Navier-Stokes flow solver.This approach combines Dynamic Mode...This article presents a novel approach for predicting transition locations over airfoils,which are used to activate turbulence model in a Reynolds-averaged Navier-Stokes flow solver.This approach combines Dynamic Mode Decomposition(DMD)with e^Ncriterion.The core idea is to use a spatial DMD analysis to extract the modes of unstable perturbations from a steady flowfield and substitute the local Linear Stability Theory(LST)analysis to quantify the spatial growth of Tollmien–Schlichting(TS)waves.Transition is assumed to take place at the stream-wise location where the most amplified mode’s N-factor reaches a prescribed threshold and a turbulence model is activated thereafter.To improve robustness,the high-order version of DMD technique(known as HODMD)is employed.A theoretical derivation is conducted to interpret how a spatial highorder DMD analysis can extract the growth rate of the unsteady perturbations.The new method is validated by transition predictions of flows over a low-speed Natural-Laminar-Flow(NLF)airfoil NLF0416 at various angles of attack and a transonic NLF airfoil NPU-LSC-72613.The transition locations predicted by our HODMD/e^Nmethod agree well with experimental data and compare favorably to those obtained by some existing methods■.It is shown that the proposed method is able to predict transition locations for flows over different types of airfoils and offers the potential for application to 3D wings as well as more complex configurations.展开更多
Machine learning has been widely utilized in flow field modeling and aerodynamic optimization.However,most applications are limited to two-dimensional problems.The dimensionality and the cost per simulation of three-d...Machine learning has been widely utilized in flow field modeling and aerodynamic optimization.However,most applications are limited to two-dimensional problems.The dimensionality and the cost per simulation of three-dimensional problems are so high that it is often too expensive to prepare sufficient samples.Therefore,transfer learning has become a promising approach to reuse well-trained two-dimensional models and greatly reduce the need for samples for threedimensional problems.This paper proposes to reuse the baseline models trained on supercritical airfoils to predict finite-span swept supercritical wings,where the simple swept theory is embedded to improve the prediction accuracy.Two baseline models are investigated:one is commonly referred to as the forward problem of predicting the pressure coefficient distribution based on the geometry,and the other is the inverse problem that predicts the geometry based on the pressure coefficient distribution.Two transfer learning strategies are compared for both baseline models.The transferred models are then tested on complete wings.The results show that transfer learning requires only approximately 500 wing samples to achieve good prediction accuracy on different wing planforms and different free stream conditions.Compared to the two baseline models,the transferred models reduce the prediction error by 60%and 80%,respectively.展开更多
A new experiment for airfoil dynamic stall is conducted by employing the advanced par- ticle image velocimetry （PIV） technology in an open-return wind tunnel. The aim of this experimen- tal investigation is to demon...A new experiment for airfoil dynamic stall is conducted by employing the advanced par- ticle image velocimetry （PIV） technology in an open-return wind tunnel. The aim of this experimen- tal investigation is to demonstrate the influences of different motion parameters on the convection velocity, position and strength of leading edge vortex （LEV） of airfoil under different dynamic stall conditions. Two different typical rotor airfoils, OA209 and SC1095, are measured at different free stream velocities, oscillation frequencies, and angles of attack. It is demonstrated by the measured data that the airfoil with larger leading edge radius could notably decrease the strength of LEV. The angle of attack （AoA） of airfoil can obviously influence the dynamic stall characteristics of airfoil, and the LEV would be effectively inhibited by decreasing the mean pitch angle. In addition, the con- vection velocity of LEV is estimated in this measurement, and the results demonstrate that the influ- ence of airfoil shape on convection velocity of LEV is limited, but the convection velocity of LEV would be increased by enlarging the oscillation frequency. Meanwhile, the convection velocity of LEV is a time variant value, and this value would increase as the LEV convects to the trailing edge of airfoil.展开更多
In the present work,a parametric numerical study is conducted in order to assess the effect of airfoil cambering on the aerodynamic performance of rigid heaving airfoils.The incompressible Navier-Stokes equations are ...In the present work,a parametric numerical study is conducted in order to assess the effect of airfoil cambering on the aerodynamic performance of rigid heaving airfoils.The incompressible Navier-Stokes equations are solved in their velocity-pressure formulation using a second-order accurate in space and time finite-difference scheme.To tackle the problem of moving boundaries,the governing equations are solved on overlapping structured grids.The numerical simulations are performed at a Reynolds number of Re=1100 and at different values of Strouhal number and reduced frequency.The results obtained show that the airfoil cambering geometric parameter has a strong influence on the average lift coefficient,while it has a smaller impact on the average thrust coefficient and propulsive efficiency of heaving airfoils.展开更多
The objective of this project is to improve the performance of the efficiency, thrust and lift of flapping wings in tandem arrangement. This research investigates the effect of the arrangement of the airfoils in tande...The objective of this project is to improve the performance of the efficiency, thrust and lift of flapping wings in tandem arrangement. This research investigates the effect of the arrangement of the airfoils in tandem on the performance of the airfoils by varying the phase difference and distance between the airfoils. Three flapping configurations from an earlier phase of a research which gives high efficiency, thrust and lift are used in the tandem simulation. It is found all the different flapping configurations show improvement in the efficiency, thrust or lift when the distance between the two airfoils and the phase angle between the heaving positions of the two airfoils are optimal. The average thrust coefficient of the tandem arrangement managed to attain more than twice that of the single one （4.84 vs. 2.05）. On the other hand, the average lift coefficient of the tandem arrangement also increased to 4.59, as compared to the original single airfoil value of 3.04. All these results obtained will aid in the design of a better ornithopter with tandem wing arrangement.展开更多
To improve aerodynamic performance of wind turbine airfoils,the shape profile characteristic of the airfoil is investigated.Application of conformal transformation,one functional and integrated expression of wind turb...To improve aerodynamic performance of wind turbine airfoils,the shape profile characteristic of the airfoil is investigated.Application of conformal transformation,one functional and integrated expression of wind turbine airfoils is presented.Using the boundary layer theory,the aerodynamic model with roughness of wind turbine airfoils is introduced by studying flow separation around the airfoil.Based on the shape expression and aerodynamic performance of airfoils,the function design of wind turbine airfoils is carried out that the maximum lift-drag ratio and low roughness sensitivity are designed objects.Three wind turbines airfoils with different thickness are gained which are used at tip part of blades.As an example,the aerodynamic performance of one designed airfoil with relative thickness of 15%is simulated in different conditions of clean surface,rough surface,laminar flow and turbulent flow.The comparison of aerodynamic performance between the designed airfoil and one popular NACA airfoil is completed which can verify the better performance of the designed airfoil and reliability of the designed method.展开更多
Simulations have been done to assess the lift, thrust and propulsive efficiency of different types of non-symmetrical airfoils under different flapping configurations. The variables involved are reduced frequency, Str...Simulations have been done to assess the lift, thrust and propulsive efficiency of different types of non-symmetrical airfoils under different flapping configurations. The variables involved are reduced frequency, Strouhal number, pitch amplitude and phase angle. In order to analyze the variables more efficiently, the design of experiments using the response surface methodology is applied. Results show that both the variables and shape of the airfoil have a profound effect on the lift, thrust, and efficiency. By using non- symmetrical airfoils, average lift coefficient as high as 2.23 can be obtained. The average thrust coefficient and efficiency also reach high values of 2.53 and 0.61, respectively. The lift production is highly dependent on the airfoil＇s shape while thrust production is influenced more heavily by the variables. Efficiency falls somewhere in between. Two-factor interac- tions are found to exist among the variables. This shows that it is not sufficient to analyze each variable individually. Vorticity diagrams are analyzed to explain the results obtained. Overall, the S1020 airfoil is able to provide relatively good efficiency and at the same time generate high thrust and lift force. These results aid in the design of a better ornithopter＇s wing.展开更多
Trailing edge serrations(TESs)are capable of noticeably suppressing the turbulent trailing edge noise induced by rotating wind turbine blades and become an integral part of a blade.However,the challenges involved in t...Trailing edge serrations(TESs)are capable of noticeably suppressing the turbulent trailing edge noise induced by rotating wind turbine blades and become an integral part of a blade.However,the challenges involved in the dimensional design of serration height 2 h,wavelengthλand flap angleϕare yet to be dealt with in a satisfactory manner.To address the problem,a general model for simulating the effects of serrations on the hydrodynamic and aeroacoustic performance is proposed due to its ease of use and relatively low requirements for user input.The solid serrations are replicated by momentum sources calculated by its aerodynamic forces.Then,a case relevant to wind turbine airfoil is examined,a hybrid improved delay detached eddy simulation(IDDES)method coupled with FW-H integration is deployed to obtain the flow features and far-field sound pressure level.It is found that the modeling method could reproduce the flow field and noise as serrated airfoil.展开更多
基金the Scientific and Technological Research Council of Turkey(TÜB˙ITAK)for support under project number:122M826to the Scientific Research Projects Unit of Erciyes University under contract No.:FYL-2023-13162 and FYL-2024-13701.
文摘Separation bubbles forming on airfoils significantly influence aerodynamic behavior,particularly at low Reynolds numbers,making their accurate prediction a critical challenge in transition modelling.This study investigates numerical modeling of a separation bubble and the effects of airfoil thickness and camber variation on the formation of the bubble dynamics at low Reynolds numbers.The numerical results were compared with the experimental results obtained from surface pressure distribution measurements,oil flow visualisation,and surface shear measurements to analyse the detailed flow behavior.The combination of pressure and flow visualisation techniques provided complementary insights,enabling a detailed characterisation of bubble formation.The results reveal that both the thickness and camber of the airfoil significantly influence the location,length,and stability of the bubble.At low Reynolds number flows(Re=0.5×10^(5)),particularly for highly cambered profiles,closer to the leading edge,separation and long bubbles were observed.As the Reynolds number increased,the separation point shifted to the leading edge,and reattachment became more likely.In numerical studies,transition models can accurately model the bubble initiation point;however,they often fail to model the bubble reattachment points accurately.This is due to the inadequacy of models that use empirical expressions for turbulence modelling,particularly in low Reynolds number flows,in their viscous modelling.In this study,it was concluded that transition onset terms,which specifically affect bubble formation,should be modified for more accurate modeling.
基金funded by University of Guanajuato through Project Convocatoria Institucional de Investigacion Cientifica 2025,161/2025.
文摘This work presents a simulation analysis using a multi-objective evolutionary algorithm for the thermo-hydraulic behavior of staggered heat sinks whose fins have NACA 0040 airfoil profile.The results were compared with a conventional pin fin heat sink with a circular profile.This study searched for the best thermo-hydraulic performance by translational and rotational positioning of the fins.It is worth mentioning that this work was carried out in two stages.In the first stage,the thermo-hydraulic behavior of the heat sink was studied moving the location of the upper array above the X-axis from to 2.25 mm and above the Y-axis from to 1.275 mm.The second stage examined-2.25-1.55the effects of fin rotation considering the results found in stage 1.However,in this second stage,both arrays were free to rotate.For the upper array,the rotation range was-25°to 25° and for the lower array the rotation range was-15° to 15°.It is worth mentioning that both stages were analyzed for a single Reynolds(Re)number value of 13,000.The optimization results using the multi-objective evolutionary algorithm showed that compared to a NACA 0040 heat sink with fixed,unrotated original configuration(C0),the NACA 0040 heat sink with any Position Configuration(PC)did not significantly improve the heat transfer.Then,the results found in the second stage showed that the effect of the rotation of both sets did not influence the increase in pressure drop.However,it was found that with the Optimal Position and Rotation Configuration(PRCoptimal),which is the optimized array from Stage 1(position)then optimized by rotation,there is a slightly higher Performance Evaluation Criterion(PEC)compared to the original C0 configuration by 7%.Finally,the proposed NACA 0040 heat sink with the optimal rotation and position setting(PRCoptimal)was found to have a PEC of 9%compared to a conventional pin fin heat sink.
基金supported by the National Natural Science Foundation of China(Grant Nos.U23A2069,12372288,12388101,and 92152301)Jilin Province Science and Technology Development Program,China(Grant No.20220301013GX)Aeronautical Science Foundation of China(Grant No.2020Z006058002)。
文摘Recent advances in contrastive language-image pretraining(CLIP)models and generative AI have demonstrated significant capabilities in cross-modal understanding and content generation.Based on these developments,this study introduces a novel framework for airfoil design via natural language interfaces.To the authors’knowledge,this study establishes the first end-to-end,bidirectional mapping between textual descriptions(e.g.,“low-drag supercritical wing for transonic conditions”)and parametric airfoil geometries represented by class-shape transformation parameters.The proposed approach integrates a CLIP-inspired architecture that aligns text embeddings with airfoil parameter spaces through contrastive learning,along with a semantically conditioned decoder that produces physically plausible airfoil geometries from latent representations.The experimental results validate the framework’s ability to generate aerodynamically plausible airfoils from natural language specifications and to classify airfoils accurately based on given textual labels.This research reduces the expertise threshold for preliminary airfoil design and highlights the potential for human-AI collaboration in aerospace engineering.
文摘For a complex flow about multi-element airfoils a mixed grid method is set up. C-type grids are produced on each element′s body and in their wakes at first, O-type grids are given in the outmost area, and H-type grids are used in middle additional areas. An algebra method is used to produce the initial grids in each area. And the girds are optimized by elliptical differential equation method. Then C-O-H zonal patched grids around multi-element airfoils are produced automatically and efficiently. A time accurate finite-volume integration method is used to solve the compressible laminar and turbulent Navier-Stokes (N-S) equations on the grids. Computational results prove the method to be effective.
基金the Scientific Research Projects Unit of Erciyes University under contract no:FDS-2022-11532 and FOA-2025-14773.
文摘This paper examines a model that combines vortex generators and leading-edge tubercles for controlling the laminar separation bubble(LSB)over an airfoil at low Reynolds numbers(Re).This new concept of passive flow control technique utilizing a tubercle and vortex generator(VG)close to the leading edge was analyzed numerically for a NACA0015 airfoil.In this study,the Shear Stress Transport(SST)turbulence model was employed in the numerical modelling.Numerical modelling was completed using the ANSYS-Fluent 18.2 solver.Analyses were conducted to investigate the flow pattern and understand the underlying LSB control phenomena that enabled the new passive flow control method to provide this significant performance benefit.The findings indicated that the new concept of passive flow control technique suppressed the formation of an LSB at the suction surface of the NACA0015 airfoil,resulting in a higher lift coefficient and improved aerodynamic performance.Improvements in LSB dynamics and aerodynamic performance through the passive flow control method lead to increased energy output and enhanced stability.
文摘This study investigates the aerodynamic efficacy enhancement of a NACA4412 airfoil using three-dimensional large eddy simulation analysis by integrating hybrid flow control techniques.The research focuses on the combined effects of cavity-based passive flow control and a dielectric barrier discharge plasma actuator aiming to increase lift and reduce drag particularly at higher Angles of Attack(AOA).Simulations were conducted at a Reynolds number of 3.1×10~6over an AOA range of 0°–20°.Four distinct cavity shapes,circular,rectangular,triangular,and curved rectangular,were analyzed,and the cavities were placed near the trailing edge on the pressure side while the plasma actuator was positioned at 2%of the chord length near the leading edge.The interaction between cavities and plasma actuation is found to mitigate flow separation by inducing vortex generation,which promotes smaller-scale vortex structures and narrows the wake.At lower AOA,cavities alone enhance lift by 20%to 30%while at higher AOA,the combination of cavities and plasma actuation achieves lift improvements of 94%to 106%.The combined system of the circular cavity and plasma actuator reduces drag at higher AOA by up to 27.56%which significantly enhances aerodynamic efficiency,and this combination yields the greatest lift to drag ratio.Vortex structure visualizations around the cavities reveal delayed flow separation and improved flow stability.Rectangular cavities alone show notable lift increases at lower AOA,and their combination with plasma actuation further reduces drag by up to 11%at higher AOA.This study demonstrates the efficacy of integrating passive and active flow control strategies for superior aerodynamic performance,highlighting their potential for highperformance airfoil applications at elevated angles of attack.
基金supported by the National Key R&D Program of China(No.2024YFC3015804)the Basic Science Center Program for“Space Robot Intelligent Manipulation”,China(No.T2388101)。
文摘Although the thin and cold Martian atmosphere provides the feasibility of rotorcraft flight on Mars,rotors designed for denser Earth atmosphere with small angles of attack hardly generate enough thrust for rotorcraft flight at conventional rotational speeds in the Martian atmosphere.In this paper,we employ the Particle Swarm Optimization(PSO)algorithm to search for the control points of the Bezier curve,completing the parameterization of the airfoil upper and lower curves based on these control points.In order to directly enhance the lift-to-drag ratio of the airfoil at high angles of attack,the NSGA-II algorithm is utilized to optimize the lift-to-drag ratio of NACA 6904 at a=17.5°,Ma=0.43,Re=7600,and CLF 5605 at a=15°,Ma=0.7,Re=7481,respectively.The two-dimensional RANS(Reynolds Average NavierStokes)and k-ωSST turbulence models are employed in the optimization process by CFD to predict the lift and drag characteristics of the airfoil in a Martian environment.Under simulated Mars atmospheric conditions(pressure of 1380 Pa,test temperature of 24°C,equivalent Mars atmospheric density at the surface of 0.0162 g/cm~3),the airfoil after optimized is subjected to rotor lift-drag characteristic tests where a single-rotor lift-drag characteristic test bench is employed for verification.The experimental results demonstrate that the RB-TB-II blade,which is obtained by optimizing the airfoil based on the RB-SWQ-I blade,exhibits a 19.6%increase in Power Loading(PL)and a 20.4%increase in Figure of Merit(FM)compared with the RB-SWQ-I blade.Based on the results of airfoil optimization,increasing the camber at the leading edge of the airfoil under high angles of attack contributes to an improved lift-to-drag ratio.
文摘Aerodynamic force and flow structures of two airfoils in a tandem configuration in flapping motions axe studied, by solving the Navier-Stokes equations in moving overset grids. Three typical phase differences between the fore- and aft-airfoil flapping cycles are considered. It is shown that: (1) in the case of no interaction (single airfoil), the time average of the vertical force coefficient over the downstroke is 2.74, which is about 3 times as large as the maximum steady-state lift coefficient of a dragonfly wing; the time average of the horizontal force coefficient is 1.97, which is also large. The reasons for the large force coefficients are the acceleration at the beginning of a stroke, the delayed stall and the 'pitching-up' motion near the end of the stroke. (2) In the cases of two-airfoils, the time-variations of the force and moment coefficients on each airfoil are broadly similar to that of the single airfoil in that the vertical force is mainly produced in downstroke and the horizontal force in upstroke, but very large differences exist due to the interaction. (3) For in-phase stroking, the major differences caused by the interaction are that the vertical force on FA in downstroke is increased and the horizontal force on FA in upstroke decreased. As a result, the magnitude of the resultant force is almost unchanged but it inclines less forward. (4) For counter stroking, the major differences are that the vertical force on AA in downstroke and the horizontal force on FA in upstroke are decreased. As a result, the magnitude of the resultant force is decreased by about 20 percent but its direction is almost unchanged. (5) For 90 degrees -phase-difference stroking, the major differences axe that the vertical force on AA in downstroke and the horizontal force on FA in upstroke axe decreased greatly and the horizontal force on AA in upstroke increased. As a result, the magnitude of the resultant force is decreased by about 28% and it inclines more forward. (6) Among the three cases of phase angles, inphase flapping produces the largest vertical force (also the largest resultant force); the 90 degrees -phase-difference flapping results in the largest horizontal force, but the smallest resultant force.
文摘A robust optimization design approach of natural laminar airfoils is developed in this paper. First, the non-uniform rational B-splines （NURBS） free form deformation method based on NURBS basis function is introduced to the airfoil parameterization. Second, aerodynamic characteristics are evaluated by solving Navier-Stokes equations, and theγ-Reθt transition model coupling with shear-stress transport （SST） turbulent model is introduced to simulate boundary layer transition. A numerical simulation of transition flow around NLF0416 airfoil is conducted to test the code. The comparison between numerical simulation results and wind tunnel test data approves the validity and applicability of the present transition model. Third, the optimization system is set up, which uses the separated particle swarm optimization （SPSO） as search algorithm and combines the Kriging models as surrogate model during optimization. The system is applied to carry out robust design about the uncertainty of lift coefficient and Mach number for NASA NLF-0115 airfoil. The data of optimized airfoil aerodynamic characteristics indicates that the optimized airfoil can maintain laminar flow stably in an uncertain range and has a wider range of low drag.
基金supported by the National Key Project of China(No.GJXM92579)the National Natural Science Foundation of China(Nos.92052203 and 11872230 and 91852108)。
文摘Natural ice accretion on the lifting surface of an aircraft is detrimental to its aerodynamic performance, as it changes the effective streamlined body. The main focus of this work considers the optimization design of airfoils under atmospheric icing conditions for the Unmanned Aerial Vehicle(UAV). The ice formation process is simulated by the Eulerian approach and the three-dimensional Myers model. A three-equation turbulence model is implemented to accurately predict the stall performance of the iced airfoil. In recognition of the real atmospheric variability in the icing parameters, the medium volume diameter of supercooled water droplets is treated as an uncertainty with an assumed probability density function. A technique of polynomial chaos expansion is used to propagate the input uncertainty through the deterministic system. The numerical results show that the multipoint/multiobjective optimization strategy can efficiently improve both the ice tolerance and the cruise performance of an airfoil. The reason for the focus on robust optimization is that the ice angle of the optimized airfoil becomes less critical to the incoming flow.The optimized airfoils are applied to a UAV platform, in which the performance improvement and the relevant key flow feature are both preserved.
基金co-supported by the National Key Research and Development Program of China(No.:2017YFB1300102)the National Natural Science Foundation of China(No.:11872314)。
文摘Introducing active flow control into the design of flapping wing is an effective way to enhance its aerodynamic performance.In this paper,a novel active flow control technology called Co-Flow Jet(CFJ)is applied to flapping airfoils.The effect of CFJ on aerodynamic performance of flapping airfoils at low Reynolds number is numerically investigated using Unsteady Reynolds Averaged Navier-Stokes(URANS)simulation with Spalart-Allmaras(SA)turbulence model.Numerical methods are validated by a NACA6415-based CFJ airfoil case and a S809 pitching airfoil case.Then NACA6415 baseline airfoil and NACA6415-based CFJ airfoil with jet-off and jet-on are simulated in flapping motion,with Reynolds number 70,000 and reduced frequency 0.2.As a result,CFJ airfoils with jet-on generally have better lift and thrust characteristics than baseline airfoils and jet-off airfoil when Cμgreater than 0.04,which results from the CFJ effect of reducing flow separation by injecting high-energy fluid into boundary layer.Besides,typical kinematic and geometric parameters,including the reduced frequency and the positions of the suction and injection slot,are systematically studied to figure out their influence on aerodynamic performance of the CFJ airfoil.And a variable Cμjet control strategy is proposed to further improve effective propulsive efficiency.Compared with using constant Cμ,an increase of effective propulsive efficiency by22.6%has been achieved by using prescribed variable CμNACA6415-based CFJ airfoil at frequency 0.2.This study may provide some guidance to performance enhancement for Flapping wing Micro Air Vehicles(FMAV).
基金supported by the National Natural Science Foundation of China (No. 11772261)the Aeronautical Science Foundation of China (No. 2016ZA53011)+1 种基金the ATCFD Project (No. 2015-F-016)the 111 Project of China (No. B17037)
文摘This article presents a novel approach for predicting transition locations over airfoils,which are used to activate turbulence model in a Reynolds-averaged Navier-Stokes flow solver.This approach combines Dynamic Mode Decomposition(DMD)with e^Ncriterion.The core idea is to use a spatial DMD analysis to extract the modes of unstable perturbations from a steady flowfield and substitute the local Linear Stability Theory(LST)analysis to quantify the spatial growth of Tollmien–Schlichting(TS)waves.Transition is assumed to take place at the stream-wise location where the most amplified mode’s N-factor reaches a prescribed threshold and a turbulence model is activated thereafter.To improve robustness,the high-order version of DMD technique(known as HODMD)is employed.A theoretical derivation is conducted to interpret how a spatial highorder DMD analysis can extract the growth rate of the unsteady perturbations.The new method is validated by transition predictions of flows over a low-speed Natural-Laminar-Flow(NLF)airfoil NLF0416 at various angles of attack and a transonic NLF airfoil NPU-LSC-72613.The transition locations predicted by our HODMD/e^Nmethod agree well with experimental data and compare favorably to those obtained by some existing methods■.It is shown that the proposed method is able to predict transition locations for flows over different types of airfoils and offers the potential for application to 3D wings as well as more complex configurations.
基金supported by the National Natural Science Foundation of China(Nos.92052203,12202243 and 11872230).
文摘Machine learning has been widely utilized in flow field modeling and aerodynamic optimization.However,most applications are limited to two-dimensional problems.The dimensionality and the cost per simulation of three-dimensional problems are so high that it is often too expensive to prepare sufficient samples.Therefore,transfer learning has become a promising approach to reuse well-trained two-dimensional models and greatly reduce the need for samples for threedimensional problems.This paper proposes to reuse the baseline models trained on supercritical airfoils to predict finite-span swept supercritical wings,where the simple swept theory is embedded to improve the prediction accuracy.Two baseline models are investigated:one is commonly referred to as the forward problem of predicting the pressure coefficient distribution based on the geometry,and the other is the inverse problem that predicts the geometry based on the pressure coefficient distribution.Two transfer learning strategies are compared for both baseline models.The transferred models are then tested on complete wings.The results show that transfer learning requires only approximately 500 wing samples to achieve good prediction accuracy on different wing planforms and different free stream conditions.Compared to the two baseline models,the transferred models reduce the prediction error by 60%and 80%,respectively.
基金supported by the National Natural Science Foundation of China(No.11272150)
文摘A new experiment for airfoil dynamic stall is conducted by employing the advanced par- ticle image velocimetry （PIV） technology in an open-return wind tunnel. The aim of this experimen- tal investigation is to demonstrate the influences of different motion parameters on the convection velocity, position and strength of leading edge vortex （LEV） of airfoil under different dynamic stall conditions. Two different typical rotor airfoils, OA209 and SC1095, are measured at different free stream velocities, oscillation frequencies, and angles of attack. It is demonstrated by the measured data that the airfoil with larger leading edge radius could notably decrease the strength of LEV. The angle of attack （AoA） of airfoil can obviously influence the dynamic stall characteristics of airfoil, and the LEV would be effectively inhibited by decreasing the mean pitch angle. In addition, the con- vection velocity of LEV is estimated in this measurement, and the results demonstrate that the influ- ence of airfoil shape on convection velocity of LEV is limited, but the convection velocity of LEV would be increased by enlarging the oscillation frequency. Meanwhile, the convection velocity of LEV is a time variant value, and this value would increase as the LEV convects to the trailing edge of airfoil.
基金supported by Maric Curie actions EST project FLUBIO(Grant:MEST-CT-2005-020228)support of the HPC-Europa++ project(Project number:211437)support of the European Community-Research Infrastructure Action of the FP7
文摘In the present work,a parametric numerical study is conducted in order to assess the effect of airfoil cambering on the aerodynamic performance of rigid heaving airfoils.The incompressible Navier-Stokes equations are solved in their velocity-pressure formulation using a second-order accurate in space and time finite-difference scheme.To tackle the problem of moving boundaries,the governing equations are solved on overlapping structured grids.The numerical simulations are performed at a Reynolds number of Re=1100 and at different values of Strouhal number and reduced frequency.The results obtained show that the airfoil cambering geometric parameter has a strong influence on the average lift coefficient,while it has a smaller impact on the average thrust coefficient and propulsive efficiency of heaving airfoils.
文摘The objective of this project is to improve the performance of the efficiency, thrust and lift of flapping wings in tandem arrangement. This research investigates the effect of the arrangement of the airfoils in tandem on the performance of the airfoils by varying the phase difference and distance between the airfoils. Three flapping configurations from an earlier phase of a research which gives high efficiency, thrust and lift are used in the tandem simulation. It is found all the different flapping configurations show improvement in the efficiency, thrust or lift when the distance between the two airfoils and the phase angle between the heaving positions of the two airfoils are optimal. The average thrust coefficient of the tandem arrangement managed to attain more than twice that of the single one （4.84 vs. 2.05）. On the other hand, the average lift coefficient of the tandem arrangement also increased to 4.59, as compared to the original single airfoil value of 3.04. All these results obtained will aid in the design of a better ornithopter with tandem wing arrangement.
基金Supported by the National Natural Science Foundation of China(No.51205430)Natural Science Foundation of ChongQing(No.cstc2011ijA70002)China Postdoctoral Science Foundation(No.2013T60842)
文摘To improve aerodynamic performance of wind turbine airfoils,the shape profile characteristic of the airfoil is investigated.Application of conformal transformation,one functional and integrated expression of wind turbine airfoils is presented.Using the boundary layer theory,the aerodynamic model with roughness of wind turbine airfoils is introduced by studying flow separation around the airfoil.Based on the shape expression and aerodynamic performance of airfoils,the function design of wind turbine airfoils is carried out that the maximum lift-drag ratio and low roughness sensitivity are designed objects.Three wind turbines airfoils with different thickness are gained which are used at tip part of blades.As an example,the aerodynamic performance of one designed airfoil with relative thickness of 15%is simulated in different conditions of clean surface,rough surface,laminar flow and turbulent flow.The comparison of aerodynamic performance between the designed airfoil and one popular NACA airfoil is completed which can verify the better performance of the designed airfoil and reliability of the designed method.
文摘Simulations have been done to assess the lift, thrust and propulsive efficiency of different types of non-symmetrical airfoils under different flapping configurations. The variables involved are reduced frequency, Strouhal number, pitch amplitude and phase angle. In order to analyze the variables more efficiently, the design of experiments using the response surface methodology is applied. Results show that both the variables and shape of the airfoil have a profound effect on the lift, thrust, and efficiency. By using non- symmetrical airfoils, average lift coefficient as high as 2.23 can be obtained. The average thrust coefficient and efficiency also reach high values of 2.53 and 0.61, respectively. The lift production is highly dependent on the airfoil＇s shape while thrust production is influenced more heavily by the variables. Efficiency falls somewhere in between. Two-factor interac- tions are found to exist among the variables. This shows that it is not sufficient to analyze each variable individually. Vorticity diagrams are analyzed to explain the results obtained. Overall, the S1020 airfoil is able to provide relatively good efficiency and at the same time generate high thrust and lift force. These results aid in the design of a better ornithopter＇s wing.
基金This work was supported by the National Natural Science Foundation of China(Grant No.51736008)“Transformational Technologies for Clean Energy and Demonstration”,Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDA21050303).
文摘Trailing edge serrations(TESs)are capable of noticeably suppressing the turbulent trailing edge noise induced by rotating wind turbine blades and become an integral part of a blade.However,the challenges involved in the dimensional design of serration height 2 h,wavelengthλand flap angleϕare yet to be dealt with in a satisfactory manner.To address the problem,a general model for simulating the effects of serrations on the hydrodynamic and aeroacoustic performance is proposed due to its ease of use and relatively low requirements for user input.The solid serrations are replicated by momentum sources calculated by its aerodynamic forces.Then,a case relevant to wind turbine airfoil is examined,a hybrid improved delay detached eddy simulation(IDDES)method coupled with FW-H integration is deployed to obtain the flow features and far-field sound pressure level.It is found that the modeling method could reproduce the flow field and noise as serrated airfoil.
