The aerodynamic force and flow structure of NACA 0012 airfoil performing an unsteady motion at low Reynolds number (Re = 100) are calculated by solving Navier-Stokes equations. The motion consists of three parts: the ...The aerodynamic force and flow structure of NACA 0012 airfoil performing an unsteady motion at low Reynolds number (Re = 100) are calculated by solving Navier-Stokes equations. The motion consists of three parts: the first translation, rotation and the second translation in the direction opposite to the first. The rotation and the second translation in this motion are expected to represent the rotation and translation of the wing-section of a hovering insect. The flow structure is used in combination with the theory of vorticity dynamics to explain the generation of unsteady aerodynamic force in the motion. During the rotation, due to the creation of strong vortices in short time, large aerodynamic force is produced and the force is almost normal to the airfoil chord. During the second translation, large lift coefficient can be maintained for certain time period and (C) over bar (L), the lift coefficient averaged over four chord lengths of travel, is larger than 2 (the corresponding steady-state lift coefficient is only 0.9). The large lift coefficient is due to two effects. The first is the delayed shedding of the stall vortex. The second is that the vortices created during the airfoil rotation and in the near wake left by previous translation form a short 'vortex street' in front of the airfoil and the 'vortex street' induces a 'wind'; against this 'wind' the airfoil translates, increasing its relative speed. The above results provide insights to the understanding of the mechanism of high-lift generation by a hovering insect.展开更多
The present study performed a numerical investigation to explore the performance enhancement of a co-flow jet(CFJ)airfoil with simple high-lift device configuration,with a specific goal to examine the feasibility and ...The present study performed a numerical investigation to explore the performance enhancement of a co-flow jet(CFJ)airfoil with simple high-lift device configuration,with a specific goal to examine the feasibility and capability of the proposed configuration for low-speed take-off and landing.Computations have been accomplished by an in-house-programmed Reynoldsaveraged Navier-Stokes solver enclosed by k-ωshear stress transport turbulence model.Three crucial geometric parameters,viz.,injection slot location,suction slot location and its angle were selected for the sake of revealing their effects on aerodynamic lift,drag,power consumption and equivalent lift-to-drag ratio.Results show that using simple high-lift devices on CFJ airfoil can significantly augment the aerodynamic associated lift and efficiency which evidences the feasibility of CFJ for short take-off and landing with small angle of attack.The injection and suction slot locations are more influential with respect to the aerodynamic performance of CFJ airfoil compared with the suction slot angle.The injection location is preferable to be located in the downstream of the pressure suction peak on leading edge to reduce the power expenditure of the pumping system for a relative higher equivalent lift-to-drag ratio.Another concluded criterion is that the suction slot should be oriented on the trailing edge flap for achieving more aerodynamic gain,meanwhile,carefully selecting this location is crucial in determining the aerodynamic enhancement of CFJ airfoil with deflected flaps.展开更多
The Adaptive Dropped Hinge Flap(ADHF) is a novel trailing edge high-lift device characterized by the integration of downward deflection spoiler and simple hinge flap, with excellent aerodynamic and mechanism performan...The Adaptive Dropped Hinge Flap(ADHF) is a novel trailing edge high-lift device characterized by the integration of downward deflection spoiler and simple hinge flap, with excellent aerodynamic and mechanism performance. In this paper, aerodynamic optimization design of an ADHF high-lift system is conducted considering the mechanism performance. Shape and settings of both takeoff and landing configurations are optimized and analyzed, with considering the kinematic constraints of ADHF mechanism, and the desired optimization results were obtained after optimization. Sensitivity analysis proves the robustness of the optimal design. Comparison shows that the ADHF design has better comprehensive performance of both mechanism and aerodynamics than the conventional Fowler flap and simple hinge flap design.展开更多
Detailed experimental measurements were conducted to study the interactions between incoming wakes and endwall secondary flow in a high-lift Low-Pressure Turbine(LPT)cascade.All of the measurements were conducted in b...Detailed experimental measurements were conducted to study the interactions between incoming wakes and endwall secondary flow in a high-lift Low-Pressure Turbine(LPT)cascade.All of the measurements were conducted in both the presence and absence of incoming wakes,and numerical analysis was performed to elucidate the flow mechanism.With increasing Reynolds number,the influence of the incoming wakes on suppressing the secondary flow gradually increased owing to the greater influence of incoming wakes on reducing the negative incidence angle at higher Reynolds numbers,leading to a lower blade loading near the leading edge and suppression of the Pressure Side(PS)leg of the horseshoe vortex.However,the effect of unsteady wakes on suppressing the profile losses gradually became weaker owing to the reduced size of the Suction Side(SS)separation bubble and increased mixing loss in the free-flow region at high Reynolds numbers.Incoming wakes clearly improved the aerodynamic performance of the low-pressure turbine cascade at low Reynolds numbers of 25,000 and 50,000.In contrast,at the high Reynolds number of 100,000,the profile loss at the midspan and mass-averaged total losses downstream of the cascade were higher in the presence of wakes than in the absence of wakes,and the unsteady wakes exerted a negative influence on the aerodynamic performance of the LPT cascade.展开更多
Numerical investigations are conducted to explore the aerodynamic characteristics of three-dimensional Co-Flow Jet(CFJ) wing with simple high-lift devices during low-speed takeoff and landing. Effects of three crucial...Numerical investigations are conducted to explore the aerodynamic characteristics of three-dimensional Co-Flow Jet(CFJ) wing with simple high-lift devices during low-speed takeoff and landing. Effects of three crucial parameters of CFJ wing, i.e., angle of attack, jet momentum and swept angle, are comprehensively examined. Additionally, the aerodynamic characteristics of two CFJ configurations, i.e., using open and discrete slots for injection, are compared. The results show that applying CFJ technique to a wing with simple high-lift device is able to generate more lift,reduce drag and enlarge stall margin with lower energy expenditure due to the super-circulation effect. Increasing the jet intensity can reduce the drag significantly, which is mainly contributed by the reaction jet force. The Oswald efficiency factor is, in some circumstances, larger than one,which indicates the potential of CFJ in reducing induced drag. Compared with clean wing configuration, using CFJ technique allows the aerodynamic force variation less sensitive to the swept angle, and such phenomenon is better observed for small swept angle region. Eventually, it is interesting to know that the discrete slotted CFJ configuration demonstrates a promising enhancement in aerodynamic performance in terms of high lift, low drag and efficiency.展开更多
High-lift siphon drainage by 4-mm internal diameter siphon hoses is a real-time, free-power, and long-term approach for slope drainage. The conventional hydraulics formula for pressurized pipe flow is generally used t...High-lift siphon drainage by 4-mm internal diameter siphon hoses is a real-time, free-power, and long-term approach for slope drainage. The conventional hydraulics formula for pressurized pipe flow is generally used to calculate the single-phase velocity of siphon flow. However, an intensive cavitation phenomenon occurs in the high-lift siphon hose and then a two-phase flow is formed. Research on the velocity of high-lift siphon flow is a prerequisite for the application of siphon drainage with a 4-mm siphon hose. Few investigations of this subject have been carried out. Hence, experiments on the high-lift （8 m〈H0〈10.3 m） siphon drainage in a 4-mm siphon hose were performed. The characteristics of siphon flow under different conditions were ob- served and test data were obtained. Comparisons between test results and calculated results showed that significant errors were given by the hydraulics formula. It is demonstrated that the effect of gas in a siphon hose should be included in the calculation of flow velocity. The findings can be used to determine the number of siphon hoses and layout of siphon drainage holes, and provide valuable information for geotechnical companies.展开更多
Three surface integral approaches of the acoustic analogies are studied to predict the noise from three concep- tual configurations of three-dimensional high-lift low-noise wings. The approaches refer to the Kirchhoff...Three surface integral approaches of the acoustic analogies are studied to predict the noise from three concep- tual configurations of three-dimensional high-lift low-noise wings. The approaches refer to the Kirchhoff method, the Ffowcs Williams and Hawkings （FW-H） method of the permeable integral surface and the Curle method that is known as a special case of the FW-H method. The first two approaches are used to compute the noise generated by the core flow region where the energetic structures exist. The last approach is adopted to predict the noise specially from the pressure perturbation on the wall. A new way to con- struct the integral surface that encloses the core region is proposed for the first two methods. Considering the local properties of the flow around the complex object-the actual wing with high-lift devices-the integral surface based on the vorticity is constructed to follow the flow structures. The surface location is discussed for the Kirchhoff method and the FW-H method because a common surface is used for them. The noise from the core flow region is studied on the basis of the dependent integral quantities, which are indicated by the Kirchhoff formulation and by the FW-H formulation. The role of each wall component on noise contribution is analyzed using the Curle formulation. Effects of the volume integral terms of Lighthill＇s stress tensors on the noise pre-diction are then evaluated by comparing the results of the Curle method with the other two methods.展开更多
Aerodynamic noise of High-Lift Devices(HLDs)is one of the main sources of airframe noise,and has immediate impacts on the airworthiness certification,environmental protection and security of commercial aircraft.In thi...Aerodynamic noise of High-Lift Devices(HLDs)is one of the main sources of airframe noise,and has immediate impacts on the airworthiness certification,environmental protection and security of commercial aircraft.In this study,a novel hybrid method is proposed for the aerodynamic noise prediction of HLD.A negative Spalart-Allmaras(S-A)turbulence model based Improved Delayed Detached Eddy Simulation(IDDES)method coupling with AFT-2017b transition model is developed,in order to elaborately simulate the complex flow field around the HLD and thus obtain the information of acoustic sources.A Farassat-Kirchhoff hybrid method is developed to filter the spurious noise sources caused by the vortex motions in solving the Ffowcs Williams-Hawkings(FW-H)equation with permeable integral surfaces,and accurately predict the far-field noise radiation of the HLD.The results of the 30P30N HLD indicate that,the computational Sound Pressure Levels(SPLs)obtained by the Farassat-Kirchhoff hybrid method conform well with the experimental ones in the spectrum for the given observation point,and are more accurate than those obtained by the Farassat 1A method.Based on the hybrid method,the acoustic directivity of the HLD of a commercial aircraft is obtained,and the variation of the SPLs in the spectrum with the deflection angle of the slat is analyzed.展开更多
This paper numerically studies the influence of the downward spoiler deflection on the boundary layer flow of a high-lift two-element airfoil consisting of a droop nose, a main wing, a downward deflecting spoiler and ...This paper numerically studies the influence of the downward spoiler deflection on the boundary layer flow of a high-lift two-element airfoil consisting of a droop nose, a main wing, a downward deflecting spoiler and a single slotted flap. Both of the boundary layer of the upper surface of the spoiler and the confluent boundary layer of the upper surface of the flap become thicker, as the downward spoiler deflection increases. Compared to the attached flow at the angle of attack of 10°, the flow of the upper surface of the spoiler becomes separated at the angle of attack of 16° when the spoiler deflection is large enough, which corresponds to the boundary layer flow reversal in velocity profiles.展开更多
The efficient utilization of propeller slipstream energy is important for improving the ultra-short takeoff and landing capability of Distributed Electric Propulsion(DEP)aircraft.This paper presents a quasi-three-dime...The efficient utilization of propeller slipstream energy is important for improving the ultra-short takeoff and landing capability of Distributed Electric Propulsion(DEP)aircraft.This paper presents a quasi-three-dimensional(2.5D)high-lift wing design approach considering the three-dimensional(3D)effects of slipstream for DEP aircraft,aiming at maximizing the comprehensive lift enhancement benefit of the airframe-propulsion coupling unit.A high-precision and efficient momentum source method is adopted to simulate the slipstream effects,and the distributed propellers are replaced by a rectangular actuator disk to reduce the difficulty of grid generation and improve the grid quality.A detailed comparison of the 2.5D and 3D configurations based on the X-57 ModⅣis performed in terms of flow characteristics and computational cost to demonstrate the rationality of the above design approach.The optimization results of the high-lift wing of the X-57 ModⅣshow that the aerodynamic performance of the landing configuration is significantly improved,for instance,the lift coefficient increases by 0.094 at the angle of attack of 7°,and 0.097 at the angle of attack of 14°.This novel approach achieves efficient and effective design of high-lift wings under the influence of distributed slipstream,which has the potential to improve the design level of DEP aircraft.展开更多
Computational prediction of stall aerodynamics in free air and in close proximity to the ground considering the 30P30N three-element high-lift configuration is carried out based on CFD simulations using the OpenFOAM c...Computational prediction of stall aerodynamics in free air and in close proximity to the ground considering the 30P30N three-element high-lift configuration is carried out based on CFD simulations using the OpenFOAM code and Fluent software. Both the attached and separated flow regimes are simulated using the Reynolds Averaged Navier-Stokes (RANS) equations closed with the Spalart-Allamaras (SA) turbulence model for static conditions and pitch oscillations at Reynolds number, <em>Re</em> = 5 x 10<sup>6</sup> and Mach number, <em>M</em> = 0.2. The effects of closeness to the ground and dynamic stall are investigated and the reduction in the lift force in close proximity to the ground is discussed.展开更多
The aerodynamic flow field downstream of a Low-Pressure High-Lift(HL)turbine cascade has been experimentally investigated for different Reynolds numbers under both steady and unsteady inflows,in order to analyse the c...The aerodynamic flow field downstream of a Low-Pressure High-Lift(HL)turbine cascade has been experimentally investigated for different Reynolds numbers under both steady and unsteady inflows,in order to analyse the cascade performance under real engine operating conditions.The Reynolds number has been varied in the range 100000<Re<300000,where lower and upper limits are typical of cruise and take-off/landing conditions,respectively.The effects induced by the incoming wakes at the reduced frequency f+=0.62 on both profile and secondary flow losses have been investigated.Total pressure,velocity and secondary kinetic energy distributions at the downstream tangential plane have been measured by means of a miniaturized 5-hole probe.These quantities provide information on both blade wake and secondary flow structures(passage and horse-shoe vortices).The analysis of the results allows the evaluation of the aerodynamic performance of the HL front-loaded blade in terms of both profile and secondary losses.展开更多
McDonnell Douglas Aerospace(MDA)high-lift model is widely used in the study of multi-element airfoil,while there is still short knowledge of ice accretion and water impingement on it.In this paper,based on two-phase f...McDonnell Douglas Aerospace(MDA)high-lift model is widely used in the study of multi-element airfoil,while there is still short knowledge of ice accretion and water impingement on it.In this paper,based on two-phase flow theory,two numerical models were presented by using both Eulerian approach and Lagrangian approach,respectively,in order to predict the water impingement efficiency on a two-dimensional(2D)multi-element high-lift airfoil.Both computational results were validated with the experiment data,which shown good agreements in the impingement limitations and tendency.The trend that how the attack angle and droplet diameter affect the feather of local water impingement characteristics on the different elements of MDA were further investigated.As shown in this research,the trends that the local impingement intensity and extent on flap of MDA varied differently as in general understanding due to the complex structures of flow field,which should be careful cognized in design of the ice protection system.展开更多
An experimental investigation on the near and far wake of a cascade of high-lift low-pressure turbine blades subjected to boundary layer separation over the suction side surface has been carried out, under steady and ...An experimental investigation on the near and far wake of a cascade of high-lift low-pressure turbine blades subjected to boundary layer separation over the suction side surface has been carried out, under steady and unsteady inflows. Two Reynolds number conditions, representative of take-off/landing and cruise operating conditions of the real engine, have been tested. The effect of upstream wake-boundary layer interaction on the wake shed from the profile has been investigated in a three-blade large-scale linear turbine cascade. The comparison between the wakes shed under steady and unsteady inflows has been performed through the analysis of mean velocity and Reynolds stress components measured at midspan of the central blade by means of a two-component crossed miniature hot-wire probe. The wake development has been analyzed in the region between 2% and 100% of the blade chord from the central blade trailing edge, aligned with the blade exit direction. Wake integral parameters, half-width and maximum velocity defects have been evaluated from the mean velocity distributions to quantify the modifications induced on the vane wake by the upstream wake. Moreover the thicknesses of the two wake shear layers have been considered separately in order to identify the effects of Reynolds number and incoming flow on the wake shape. The self-preserving state of the wake has been looked at, taking into account the different thicknesses of the two shear layers. The evaluation of the power density spectra of the velocity fluctuations allowed the study of the wake unsteady behavior, and the detection of the effects induced by the different operating conditions on the trailing edge vortex shedding.展开更多
The suction side boundary layer evolution of a high-lift low-pressure turbine cascade has been experimentally in- vestigated at low and high free-stream turbulence intensity conditions. Measurements have been carded o...The suction side boundary layer evolution of a high-lift low-pressure turbine cascade has been experimentally in- vestigated at low and high free-stream turbulence intensity conditions. Measurements have been carded out in order to analyze the boundary layer transition and separation processes at a low Reynolds nttmber, under both steady and unsteady inflows. Static pressure distributions along the blade surfaces as well as total pressure distri- butions in a downstream tangential plane have been measured to evaluate the overall aerodynamic efficiency of the blade for the different conditions. Particle. Image Velocimetry has been adopted to analyze the time-mean and time-varying velocity fields. The flow field has been surveyed in two orthogonal planes （a blade-to-blade plane and a wall-parallel one）. These measurements allow the identification of the Kelvin-Helmholtz large scale cohe- rent structures shed as a consequence of the boundary layer laminar separation under steady inflow, as well as the investigation of the three-dimensional effects induced by the intermittent passage of low and high speed streaks. A close inspection of the time-mean velocity profiles as well as of the boundary layer integral parameters helps to characterize the suction side boundary layer state, thus justifying the influence of free-stream turbulence intensity on the blade aerodynamic losses measured under steady and unsteady inflows.展开更多
基金The project supported by the National Natural Science Foundation of China (19725210)
文摘The aerodynamic force and flow structure of NACA 0012 airfoil performing an unsteady motion at low Reynolds number (Re = 100) are calculated by solving Navier-Stokes equations. The motion consists of three parts: the first translation, rotation and the second translation in the direction opposite to the first. The rotation and the second translation in this motion are expected to represent the rotation and translation of the wing-section of a hovering insect. The flow structure is used in combination with the theory of vorticity dynamics to explain the generation of unsteady aerodynamic force in the motion. During the rotation, due to the creation of strong vortices in short time, large aerodynamic force is produced and the force is almost normal to the airfoil chord. During the second translation, large lift coefficient can be maintained for certain time period and (C) over bar (L), the lift coefficient averaged over four chord lengths of travel, is larger than 2 (the corresponding steady-state lift coefficient is only 0.9). The large lift coefficient is due to two effects. The first is the delayed shedding of the stall vortex. The second is that the vortices created during the airfoil rotation and in the near wake left by previous translation form a short 'vortex street' in front of the airfoil and the 'vortex street' induces a 'wind'; against this 'wind' the airfoil translates, increasing its relative speed. The above results provide insights to the understanding of the mechanism of high-lift generation by a hovering insect.
基金supported by the National Natural Science Foundation of China(No.11672133)the Research Funds for Central Universities(No.kfjj20180104)support from Rotor Aerodynamics Key Laboratory(No.RAL20190202-2)。
文摘The present study performed a numerical investigation to explore the performance enhancement of a co-flow jet(CFJ)airfoil with simple high-lift device configuration,with a specific goal to examine the feasibility and capability of the proposed configuration for low-speed take-off and landing.Computations have been accomplished by an in-house-programmed Reynoldsaveraged Navier-Stokes solver enclosed by k-ωshear stress transport turbulence model.Three crucial geometric parameters,viz.,injection slot location,suction slot location and its angle were selected for the sake of revealing their effects on aerodynamic lift,drag,power consumption and equivalent lift-to-drag ratio.Results show that using simple high-lift devices on CFJ airfoil can significantly augment the aerodynamic associated lift and efficiency which evidences the feasibility of CFJ for short take-off and landing with small angle of attack.The injection and suction slot locations are more influential with respect to the aerodynamic performance of CFJ airfoil compared with the suction slot angle.The injection location is preferable to be located in the downstream of the pressure suction peak on leading edge to reduce the power expenditure of the pumping system for a relative higher equivalent lift-to-drag ratio.Another concluded criterion is that the suction slot should be oriented on the trailing edge flap for achieving more aerodynamic gain,meanwhile,carefully selecting this location is crucial in determining the aerodynamic enhancement of CFJ airfoil with deflected flaps.
基金supported by the National Natural Science Foundation of China(Nos.11872230,91852108,91952302,92052203)the Aeronautical Science Foundation of China(No.2020Z006058002)。
文摘The Adaptive Dropped Hinge Flap(ADHF) is a novel trailing edge high-lift device characterized by the integration of downward deflection spoiler and simple hinge flap, with excellent aerodynamic and mechanism performance. In this paper, aerodynamic optimization design of an ADHF high-lift system is conducted considering the mechanism performance. Shape and settings of both takeoff and landing configurations are optimized and analyzed, with considering the kinematic constraints of ADHF mechanism, and the desired optimization results were obtained after optimization. Sensitivity analysis proves the robustness of the optimal design. Comparison shows that the ADHF design has better comprehensive performance of both mechanism and aerodynamics than the conventional Fowler flap and simple hinge flap design.
基金provided by the National Natural Science Foundation of China(Nos.51876202 and 51836008)。
文摘Detailed experimental measurements were conducted to study the interactions between incoming wakes and endwall secondary flow in a high-lift Low-Pressure Turbine(LPT)cascade.All of the measurements were conducted in both the presence and absence of incoming wakes,and numerical analysis was performed to elucidate the flow mechanism.With increasing Reynolds number,the influence of the incoming wakes on suppressing the secondary flow gradually increased owing to the greater influence of incoming wakes on reducing the negative incidence angle at higher Reynolds numbers,leading to a lower blade loading near the leading edge and suppression of the Pressure Side(PS)leg of the horseshoe vortex.However,the effect of unsteady wakes on suppressing the profile losses gradually became weaker owing to the reduced size of the Suction Side(SS)separation bubble and increased mixing loss in the free-flow region at high Reynolds numbers.Incoming wakes clearly improved the aerodynamic performance of the low-pressure turbine cascade at low Reynolds numbers of 25,000 and 50,000.In contrast,at the high Reynolds number of 100,000,the profile loss at the midspan and mass-averaged total losses downstream of the cascade were higher in the presence of wakes than in the absence of wakes,and the unsteady wakes exerted a negative influence on the aerodynamic performance of the LPT cascade.
基金the National Natural Science Foundation of China (No. 11672133)the Fundamental Research Funds for the Central Universities, China (No. kfjj20180104)support from Rotor Aerodynamics Key Laboratory, China (No. RAL20190202-2/RAL20190101-1)
文摘Numerical investigations are conducted to explore the aerodynamic characteristics of three-dimensional Co-Flow Jet(CFJ) wing with simple high-lift devices during low-speed takeoff and landing. Effects of three crucial parameters of CFJ wing, i.e., angle of attack, jet momentum and swept angle, are comprehensively examined. Additionally, the aerodynamic characteristics of two CFJ configurations, i.e., using open and discrete slots for injection, are compared. The results show that applying CFJ technique to a wing with simple high-lift device is able to generate more lift,reduce drag and enlarge stall margin with lower energy expenditure due to the super-circulation effect. Increasing the jet intensity can reduce the drag significantly, which is mainly contributed by the reaction jet force. The Oswald efficiency factor is, in some circumstances, larger than one,which indicates the potential of CFJ in reducing induced drag. Compared with clean wing configuration, using CFJ technique allows the aerodynamic force variation less sensitive to the swept angle, and such phenomenon is better observed for small swept angle region. Eventually, it is interesting to know that the discrete slotted CFJ configuration demonstrates a promising enhancement in aerodynamic performance in terms of high lift, low drag and efficiency.
基金Project supported by the National ＂Twelfth Five-Year＂ Plan for Science ＆ Technology Support Program of China （No. 2012BAK10B06） and the National Natural Science Foundation of China （No. 41272336）
文摘High-lift siphon drainage by 4-mm internal diameter siphon hoses is a real-time, free-power, and long-term approach for slope drainage. The conventional hydraulics formula for pressurized pipe flow is generally used to calculate the single-phase velocity of siphon flow. However, an intensive cavitation phenomenon occurs in the high-lift siphon hose and then a two-phase flow is formed. Research on the velocity of high-lift siphon flow is a prerequisite for the application of siphon drainage with a 4-mm siphon hose. Few investigations of this subject have been carried out. Hence, experiments on the high-lift （8 m〈H0〈10.3 m） siphon drainage in a 4-mm siphon hose were performed. The characteristics of siphon flow under different conditions were ob- served and test data were obtained. Comparisons between test results and calculated results showed that significant errors were given by the hydraulics formula. It is demonstrated that the effect of gas in a siphon hose should be included in the calculation of flow velocity. The findings can be used to determine the number of siphon hoses and layout of siphon drainage holes, and provide valuable information for geotechnical companies.
基金supported by the Clean Sky Joint Undertaking(CSJU)(CS-GA-2009-255714)
文摘Three surface integral approaches of the acoustic analogies are studied to predict the noise from three concep- tual configurations of three-dimensional high-lift low-noise wings. The approaches refer to the Kirchhoff method, the Ffowcs Williams and Hawkings （FW-H） method of the permeable integral surface and the Curle method that is known as a special case of the FW-H method. The first two approaches are used to compute the noise generated by the core flow region where the energetic structures exist. The last approach is adopted to predict the noise specially from the pressure perturbation on the wall. A new way to con- struct the integral surface that encloses the core region is proposed for the first two methods. Considering the local properties of the flow around the complex object-the actual wing with high-lift devices-the integral surface based on the vorticity is constructed to follow the flow structures. The surface location is discussed for the Kirchhoff method and the FW-H method because a common surface is used for them. The noise from the core flow region is studied on the basis of the dependent integral quantities, which are indicated by the Kirchhoff formulation and by the FW-H formulation. The role of each wall component on noise contribution is analyzed using the Curle formulation. Effects of the volume integral terms of Lighthill＇s stress tensors on the noise pre-diction are then evaluated by comparing the results of the Curle method with the other two methods.
基金This study was co-supported by the Shanghai Pujiang Program,China(No.20PJ1402000)the Open Project of Key Laboratory of Aerodynamic Noise Control,China(No.ANCL20200302)Shanghai Key Laboratory of Aircraft Engine Digital Twin,China(No.HT-6FTX 0021-2021).
文摘Aerodynamic noise of High-Lift Devices(HLDs)is one of the main sources of airframe noise,and has immediate impacts on the airworthiness certification,environmental protection and security of commercial aircraft.In this study,a novel hybrid method is proposed for the aerodynamic noise prediction of HLD.A negative Spalart-Allmaras(S-A)turbulence model based Improved Delayed Detached Eddy Simulation(IDDES)method coupling with AFT-2017b transition model is developed,in order to elaborately simulate the complex flow field around the HLD and thus obtain the information of acoustic sources.A Farassat-Kirchhoff hybrid method is developed to filter the spurious noise sources caused by the vortex motions in solving the Ffowcs Williams-Hawkings(FW-H)equation with permeable integral surfaces,and accurately predict the far-field noise radiation of the HLD.The results of the 30P30N HLD indicate that,the computational Sound Pressure Levels(SPLs)obtained by the Farassat-Kirchhoff hybrid method conform well with the experimental ones in the spectrum for the given observation point,and are more accurate than those obtained by the Farassat 1A method.Based on the hybrid method,the acoustic directivity of the HLD of a commercial aircraft is obtained,and the variation of the SPLs in the spectrum with the deflection angle of the slat is analyzed.
文摘This paper numerically studies the influence of the downward spoiler deflection on the boundary layer flow of a high-lift two-element airfoil consisting of a droop nose, a main wing, a downward deflecting spoiler and a single slotted flap. Both of the boundary layer of the upper surface of the spoiler and the confluent boundary layer of the upper surface of the flap become thicker, as the downward spoiler deflection increases. Compared to the attached flow at the angle of attack of 10°, the flow of the upper surface of the spoiler becomes separated at the angle of attack of 16° when the spoiler deflection is large enough, which corresponds to the boundary layer flow reversal in velocity profiles.
文摘The efficient utilization of propeller slipstream energy is important for improving the ultra-short takeoff and landing capability of Distributed Electric Propulsion(DEP)aircraft.This paper presents a quasi-three-dimensional(2.5D)high-lift wing design approach considering the three-dimensional(3D)effects of slipstream for DEP aircraft,aiming at maximizing the comprehensive lift enhancement benefit of the airframe-propulsion coupling unit.A high-precision and efficient momentum source method is adopted to simulate the slipstream effects,and the distributed propellers are replaced by a rectangular actuator disk to reduce the difficulty of grid generation and improve the grid quality.A detailed comparison of the 2.5D and 3D configurations based on the X-57 ModⅣis performed in terms of flow characteristics and computational cost to demonstrate the rationality of the above design approach.The optimization results of the high-lift wing of the X-57 ModⅣshow that the aerodynamic performance of the landing configuration is significantly improved,for instance,the lift coefficient increases by 0.094 at the angle of attack of 7°,and 0.097 at the angle of attack of 14°.This novel approach achieves efficient and effective design of high-lift wings under the influence of distributed slipstream,which has the potential to improve the design level of DEP aircraft.
文摘Computational prediction of stall aerodynamics in free air and in close proximity to the ground considering the 30P30N three-element high-lift configuration is carried out based on CFD simulations using the OpenFOAM code and Fluent software. Both the attached and separated flow regimes are simulated using the Reynolds Averaged Navier-Stokes (RANS) equations closed with the Spalart-Allamaras (SA) turbulence model for static conditions and pitch oscillations at Reynolds number, <em>Re</em> = 5 x 10<sup>6</sup> and Mach number, <em>M</em> = 0.2. The effects of closeness to the ground and dynamic stall are investigated and the reduction in the lift force in close proximity to the ground is discussed.
文摘The aerodynamic flow field downstream of a Low-Pressure High-Lift(HL)turbine cascade has been experimentally investigated for different Reynolds numbers under both steady and unsteady inflows,in order to analyse the cascade performance under real engine operating conditions.The Reynolds number has been varied in the range 100000<Re<300000,where lower and upper limits are typical of cruise and take-off/landing conditions,respectively.The effects induced by the incoming wakes at the reduced frequency f+=0.62 on both profile and secondary flow losses have been investigated.Total pressure,velocity and secondary kinetic energy distributions at the downstream tangential plane have been measured by means of a miniaturized 5-hole probe.These quantities provide information on both blade wake and secondary flow structures(passage and horse-shoe vortices).The analysis of the results allows the evaluation of the aerodynamic performance of the HL front-loaded blade in terms of both profile and secondary losses.
基金Many thanks to Prof.Tom Shih at Purdue University for providing guidance in grid generation and flow field simulation and the financial support from The Fundamental Research Funds for the Central Universities at Beihang University,number:YWF-14-JTXY-009.
文摘McDonnell Douglas Aerospace(MDA)high-lift model is widely used in the study of multi-element airfoil,while there is still short knowledge of ice accretion and water impingement on it.In this paper,based on two-phase flow theory,two numerical models were presented by using both Eulerian approach and Lagrangian approach,respectively,in order to predict the water impingement efficiency on a two-dimensional(2D)multi-element high-lift airfoil.Both computational results were validated with the experiment data,which shown good agreements in the impingement limitations and tendency.The trend that how the attack angle and droplet diameter affect the feather of local water impingement characteristics on the different elements of MDA were further investigated.As shown in this research,the trends that the local impingement intensity and extent on flap of MDA varied differently as in general understanding due to the complex structures of flow field,which should be careful cognized in design of the ice protection system.
文摘An experimental investigation on the near and far wake of a cascade of high-lift low-pressure turbine blades subjected to boundary layer separation over the suction side surface has been carried out, under steady and unsteady inflows. Two Reynolds number conditions, representative of take-off/landing and cruise operating conditions of the real engine, have been tested. The effect of upstream wake-boundary layer interaction on the wake shed from the profile has been investigated in a three-blade large-scale linear turbine cascade. The comparison between the wakes shed under steady and unsteady inflows has been performed through the analysis of mean velocity and Reynolds stress components measured at midspan of the central blade by means of a two-component crossed miniature hot-wire probe. The wake development has been analyzed in the region between 2% and 100% of the blade chord from the central blade trailing edge, aligned with the blade exit direction. Wake integral parameters, half-width and maximum velocity defects have been evaluated from the mean velocity distributions to quantify the modifications induced on the vane wake by the upstream wake. Moreover the thicknesses of the two wake shear layers have been considered separately in order to identify the effects of Reynolds number and incoming flow on the wake shape. The self-preserving state of the wake has been looked at, taking into account the different thicknesses of the two shear layers. The evaluation of the power density spectra of the velocity fluctuations allowed the study of the wake unsteady behavior, and the detection of the effects induced by the different operating conditions on the trailing edge vortex shedding.
文摘The suction side boundary layer evolution of a high-lift low-pressure turbine cascade has been experimentally in- vestigated at low and high free-stream turbulence intensity conditions. Measurements have been carded out in order to analyze the boundary layer transition and separation processes at a low Reynolds nttmber, under both steady and unsteady inflows. Static pressure distributions along the blade surfaces as well as total pressure distri- butions in a downstream tangential plane have been measured to evaluate the overall aerodynamic efficiency of the blade for the different conditions. Particle. Image Velocimetry has been adopted to analyze the time-mean and time-varying velocity fields. The flow field has been surveyed in two orthogonal planes （a blade-to-blade plane and a wall-parallel one）. These measurements allow the identification of the Kelvin-Helmholtz large scale cohe- rent structures shed as a consequence of the boundary layer laminar separation under steady inflow, as well as the investigation of the three-dimensional effects induced by the intermittent passage of low and high speed streaks. A close inspection of the time-mean velocity profiles as well as of the boundary layer integral parameters helps to characterize the suction side boundary layer state, thus justifying the influence of free-stream turbulence intensity on the blade aerodynamic losses measured under steady and unsteady inflows.
