<span><span style="font-family:;" "=""><span style="font-family:Verdana;"></span><span style="font-family:Verdana;">When there is a wall near ...<span><span style="font-family:;" "=""><span style="font-family:Verdana;"></span><span style="font-family:Verdana;">When there is a wall near the jet, it deflects and flows while being attached to the wall owing to the Coanda effect. The flow characteristics of the incompressible and two-imensional (2D) Coanda-reattached jets have been considerably explained. However, 2D supersonic under-expanded jets, reattached to side walls, have not been sufficiently investigated. These jets are used in gas-atomization to produce fine metal powder particles of several micrometers to several tens micrometers. In this case, the supersonic under-expanded jets are issued from an annular nozzle, which is set around a vertically in</span><span style="font-family:Verdana;">stalled circular nozzle for molten metal. The jet flow at the center</span><span style="font-family:Verdana;"> cross</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">-</span></span></span><span><span><span style="font-family:;" "=""><span style="font-family:Verdana;">section of the annular jet resembles a 2D Coanda-reattached jet that deflects and attaches on the central axis. In this study, the flow characteristics of a supersonic under-expanded Coanda air jet from a 2D nozzle that reattaches to an offset side wall are elucidated through experiment and numerical analysis. For numerical analysis, we show how much it can express experimental results. The effects of supply pressure </span><i><span style="font-family:Verdana;">P</span><span style="font-family:Verdana;"><sub></sub></span><span style="font-family:Verdana;"></span></i><sub><span style="font-family:Verdana;">0</span><span style="font-family:Verdana;"></span></sub></span><span style="font-family:Verdana;"></span><span style="font-family:Verdana;"> on the flow characteristics such as the flow pattern, size of shock cell, reattachment distance, and velocity and pressure distributions, etc. are examined. The flow pattern was visualized by Schlieren method and the velocity distribution was measured using a Pitot tube. These results will be also useful in understanding the flow characteristics of a gas-atomization annular nozzle approximately.</span></span></span>展开更多
To increase the gripping area of noncontact end grippers(NCEGs), an array-type NCEG based on the Coanda mechanism is proposed, and its performance in gripping different garment fabrics(GFs) is studied. Firstly, the st...To increase the gripping area of noncontact end grippers(NCEGs), an array-type NCEG based on the Coanda mechanism is proposed, and its performance in gripping different garment fabrics(GFs) is studied. Firstly, the structure and the working mechanism of a single Coanda-based NCEG were analyzed. Secondly, four such grippers were arranged in array to form a minimum gripping unit. Then, the structure of the connecting plate(CP) to the gripper was optimized by simulation analysis to exclude airflow interference, and the adsorption performance of GFs with different fabric parameters was measured. Finally, the experimental results were analyzed to verify the scientific validity and the feasibility of the array-type arrangement. The results show that compared with other NCEGs, the array-type ones based on the Coanda mechanism are better at gripping various large-area GFs and offer better adsorption performance. This innovation provides a new solution to the problem of insufficient gripping area in GF gripping and is very important for improving the production efficiency of garment processing.展开更多
The present study investigated the effect of geometrical and non-geometrical parameters on the thrust performance of a pump-valve propulsion device consisting of a Coanda effect valve(CEV)and a pump.A more accurate th...The present study investigated the effect of geometrical and non-geometrical parameters on the thrust performance of a pump-valve propulsion device consisting of a Coanda effect valve(CEV)and a pump.A more accurate theoretical model was also developed to predict the thrust of the pump-valve device.Firstly,a rough thrust model was developed based on existing theory to predict the thrust and energy loss generated by the pump-valve device under different exit and nozzle areas.Considering the limitations of the theoretical analysis,numerical simulations were carried out to evaluate the effect of various geometrical and non-geometrical parameters,including nozzle shape,nozzle area,control port width,exit area,inlet flow rate,etc.,on the thrust performance of the CEV and the pump-valve device.Due to the margin between simulation thrusts and theoretical thrusts,we built an experimental platform and carried out relevant experiments.The experimental data verified the simulation results,and on this basis,the original thrust prediction model was corrected.展开更多
Gas turbine is a promising device for power generation and propulsion either using traditional or renewable energy fuels.One of its key problems is the flow instability of compressors especially with the increase in b...Gas turbine is a promising device for power generation and propulsion either using traditional or renewable energy fuels.One of its key problems is the flow instability of compressors especially with the increase in blade load and changeable working environment.To intelligently and efficiently inhibit flow separation and enhance the pressure rise ability of highly loaded compressors under variable operating conditions,a novel flow control technique termed as adaptive Coanda jet control(ACJC)is proposed in this paper for a compressor stator cascade with a high diffusion factor of 0.66.To realize the ACJC strategy,an incidence angle(IA)prediction model and an optimal injection mass flow rate(OIMFR)prediction model are established by adopting single factor analysis of variance,principal component analysis and Back Propagation Neural Network(BPNN)methods.Two inlet Mach numbers including 0.1 and 0.4 are considered to represent incompressible and compressible flow conditions,and different inlet incidence angles are involved to model various off-design working situations of the real compressor.Effectiveness of the ACJC system is evaluated using numerical simulations are performed to understand the effects of the injection mass flow ratio on the flow field and aerodynamic performance of the blade cascade.Results indicate that the ACJC system can accurately predict the optimal injection mass flow ratio that can achieve the minimum flow loss at each incidence angle.Compared to the cascade without ACJC under the incidence angel of 5,the optimal injection mass flow ratio being 1.27%and 1.20%can reduce the total pressure loss coefficient by 18.88%and 21.56%for incoming Mach number being 0.1 and 0.4,respectively.展开更多
针对无叶风扇气动噪声过大的问题,开展基于CST(Class Function/Shape Function Transformation,CST)参数化方法的柯恩达面气动噪声敏感性分析。首先,以NACA0012翼型及样条曲线构造柯恩达面,建立无叶风扇的风圈截面及三维模型。然后,通...针对无叶风扇气动噪声过大的问题,开展基于CST(Class Function/Shape Function Transformation,CST)参数化方法的柯恩达面气动噪声敏感性分析。首先,以NACA0012翼型及样条曲线构造柯恩达面,建立无叶风扇的风圈截面及三维模型。然后,通过数值模拟分析柯恩达面处的流动情况及气动噪声,并通过试验验证数值计算的准确性。最后,建立柯恩达面参数化模型,并以气动噪声为目标响应,采用Sobol法与Kriging代理模型相结合的方法,计算参数化模型中Bernstein多项式系数的一阶灵敏度系数和总灵敏度系数,找出对气动噪声影响较大的参数。结果表明,影响柯恩达面处气动噪声的主要因素依次为风圈截面的厚度、前缘半径、后缘厚度。展开更多
Mounds of spatter are generated in laser powder-bed fusion(L-PBF)additive manufacturing,which reduces build quality and laser lifetime.Due to the lack of supplemental airflow above the chamber,the conventional build c...Mounds of spatter are generated in laser powder-bed fusion(L-PBF)additive manufacturing,which reduces build quality and laser lifetime.Due to the lack of supplemental airflow above the chamber,the conventional build chamber with a single gas inlet exhibits a pronounced tendency for gas to flow upward near the outlet.This phenomenon results in the formation of a large vortex within the build chamber.The vortex leads to the chaotic motion trajectory of the spatter in the build chamber.The design defects of the existing build chamber based on dual gas inlets are shown in this paper.We established a coupled computational fluid dynamics-discrete phase model(CFD-DPM)model to optimize the build chamber by adjusting the position and structure of the second gas inlet.The homogeneity of the flow is increased with a distance of 379 mm between the two inlets and a wider-reaching second inlet.The Coanda effect is also crucial in the spatter-removal process.The Coanda effect is reduced by modifying the right sidewall of the build chamber and increasing the pressure difference between the inlet and outlet.Finally,we found that the spatter-removal rate rose from 8.9%to 76.1%between the conventional build chamber with a single gas inlet and the optimized build chamber with two gas inlets.展开更多
The Coanda effect has long been employed in the aerospace applications to improve the performances of various devices. This effect is the ability of a flow to follow a curved contour without separation and has well be...The Coanda effect has long been employed in the aerospace applications to improve the performances of various devices. This effect is the ability of a flow to follow a curved contour without separation and has well been utilized in ejectors where a high speed jet of fluid emerges from a nozzle in the ejector body, follows a curved surface and drags the secondary flow into the ejector. In Coanda ejectors, the secondary flow is dragged in the ejector due to the primary flow momentum. The transfer of momentum from the primary flow to the secondary flow takes place through turbulent mixing and viscous effects. The secondary flow is then dragged by turbulent shear force of the ejector while being mixed with the primary flow by the persistence of a large turbulent intensity throughout the ejector. The performance of a Coanda ejector is studied mainly based on how well it drags the secondary flow and the amount of mixing between the two flows at the ejector exit. The aim of the present study is to investigate the influence of various geometric parameters and pressure ratios on the Coanda ejector performance. The effect of various factors, such as, the pressure ratio, primary nozzle and ejector configurations on the system performance has been evaluated based on a performance parameter defined elsewhere. The performance of the Coanda ejector strongly depends on the primary nozzle configuration and the pressure ratio. The mixing layer growth plays a major role in optimizing the performance of the Coanda ejector as it decides the ratio of secondary mass flow rate to primary mass flow rate and the mixing length.展开更多
To control the film thickness of zinc in the process of continuous hot-dip galvanizing, it is known from the early days that the gas wiping through an air knife is the most effective one. The gas wiping using in galva...To control the film thickness of zinc in the process of continuous hot-dip galvanizing, it is known from the early days that the gas wiping through an air knife is the most effective one. The gas wiping using in galvanizing process brings about a problem of splashing from the strip edge for a certain high speed of coating. So, in the present study, the effects of the deflection angle of Coanda nozzle on jet structure and the distribution of impinging pres- sure at the plate surface are investigated numerically and experimentally. In numerical analysis, the governing equations consisted of three-dimensional time dependent full Navier-Stokes equations, standard k-ε turbulence model to solve turbulent stTess and so on are employed. In experiment, 16 channel pressure scanning valve and 3-axis auto traversing unit are used to measure the impinging pressure at the strip surface. As a result, it is found that the smaller the deflection angle for the same nozzle slit of air knife is, the larger the impinging pressure is. To reduce the size of separation bubble and to enhance the cutting ability, it is recommendable to use an air knife with the Coanda nozzle.展开更多
Techniques using Coanda effect have been applied to the fiuid control devices. In this field, experimental studies were so far performed for the spiral jet obtained by the Coanda jet issuing from a conical cylinder wi...Techniques using Coanda effect have been applied to the fiuid control devices. In this field, experimental studies were so far performed for the spiral jet obtained by the Coanda jet issuing from a conical cylinder with an annular slit, thrust vectoring of supersonic Coanda jets and so on. It is important from the viewpoints of effective applications to investigate the characteristics of the supersonic Coanda jet in detail. In the present study the effects of pressure ratios and nozzle configurations on the characteristics of the supersonic Coanda jet have been investigated experhoentally by a schlieren optical method and pressure measurements. Furthermore, Navier-Stokes equations were solved numerically using a 2nd-order TVD finite-volume scheme with a 3rd-rorder three stage Runge-Kutta method for time integration. k - ε model was used in the computations. The effects of initial conditions on Coandaflow were investigated numerically As a result, the simulated flow helds were compared with experimental data in good agreement qualitatively.展开更多
Coanda jet flap is an effective flow control technique,which offers pressurized high streamwise velocity to eliminate the boundary layer flow separation and increase the aerodynamic loading of compressor blades.Tradit...Coanda jet flap is an effective flow control technique,which offers pressurized high streamwise velocity to eliminate the boundary layer flow separation and increase the aerodynamic loading of compressor blades.Traditionally,there is only single-jet flap on the blade suction side.A novel Coanda double-jet flap configuration combining the front-jet slot near the blade leading edge and the rear-jet slot near the blade trailing edge is proposed and investigated in this paper.The reference highly loaded compressor profile is the Zierke&Deutsch double-circular-arc airfoil with the diffusion factor of 0.66.Firstly,three types of Coanda jet flap configurations including front-jet,rear-jet and the novel double-jet flaps are designed based on the 2D flow fields in the highly loaded compressor blade passage.The Back Propagation Neural Network(BPNN)combined with the genetic algorithm(GA)is adopted to obtain the optimal geometry for each type of Coanda jet flap configuration.Numerical simulations are then performed to understand the effects of the three optimal Coanda jet flaps on the compressor airfoil performance.Results indicate all the three types of Coanda jet flaps effectively improve the aerodynamic performance of the highly loaded airfoil,and the Coanda double-jet flap behaves best in controlling the boundary layer flow separation.At the inlet flow condition with incidence angle of 5°,the total pressure loss coefficient is reduced by 52.5%and the static pressure rise coefficient is increased by 25.7%with Coanda double-jet flap when the normalized jet mass flow ratio of the front jet and the rear jet is equal to 1.5%and 0.5%,respectively.The impacts of geometric parameters and jet mass flow ratios on the airfoil aerodynamic performance are further analyzed.It is observed that the geometric design parameters of Coanda double-jet flap determine airfoil thickness and jet slot position,which plays the key role in supressing flow separation on the airfoil suction side.Furthermore,there exists an optimal combination of front-jet and rear-jet mass flow ratios to achieve the minimum flow loss at each incidence angle of incoming flow.These results indicate that Coanda double-jet flap combining the adjust of jet mass flow rate varying with the incidence angle of incoming flow would be a promising adaptive flow control technique.展开更多
The unique Coanda surface has a great influence on the performance of bladeless fan.However,there is few studies to explain the relationship between the performance and Coanda surface curvature at present.In order to ...The unique Coanda surface has a great influence on the performance of bladeless fan.However,there is few studies to explain the relationship between the performance and Coanda surface curvature at present.In order to gain a qualitative understanding of effect of the curvature on the performance of bladeless fan,numerical studies are performed in this paper.Firstly,three-dimensional numerical simulation is done by Fluent software.For the purpose to obtain detailed information of the flow field around the Coanda surface,two-dimensional numerical simulation is also conducted.Five types of Coanda surfaces with different curvature are designed,and the flow behaviour and the performance of them are analyzed and compared with those of the prototype.The analysis indicates that the curvature of Coanda surface is strongly related to blowing performance,It is found that there is an optimal curvature of Coanda surfaces among the studied models.Simulation result shows that there is a special low pressure region.With increasing curvature in Y direction,several low pressure regions gradually enlarged,then begin to merge slowly,and finally form a large area of low pressure.From the analyses of streamlines and velocity angle,it is found that the magnitude of the curvature affects the flow direction and reasonable curvature can induce fluid flow close to the wall.Thus,it leads to that the curvature of the streamlines is consistent with that of Coanda surface.Meanwhile,it also causes the fluid movement towards the most suitable direction.This study will provide useful information to performance improvements of bladeless fans.展开更多
文摘<span><span style="font-family:;" "=""><span style="font-family:Verdana;"></span><span style="font-family:Verdana;">When there is a wall near the jet, it deflects and flows while being attached to the wall owing to the Coanda effect. The flow characteristics of the incompressible and two-imensional (2D) Coanda-reattached jets have been considerably explained. However, 2D supersonic under-expanded jets, reattached to side walls, have not been sufficiently investigated. These jets are used in gas-atomization to produce fine metal powder particles of several micrometers to several tens micrometers. In this case, the supersonic under-expanded jets are issued from an annular nozzle, which is set around a vertically in</span><span style="font-family:Verdana;">stalled circular nozzle for molten metal. The jet flow at the center</span><span style="font-family:Verdana;"> cross</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">-</span></span></span><span><span><span style="font-family:;" "=""><span style="font-family:Verdana;">section of the annular jet resembles a 2D Coanda-reattached jet that deflects and attaches on the central axis. In this study, the flow characteristics of a supersonic under-expanded Coanda air jet from a 2D nozzle that reattaches to an offset side wall are elucidated through experiment and numerical analysis. For numerical analysis, we show how much it can express experimental results. The effects of supply pressure </span><i><span style="font-family:Verdana;">P</span><span style="font-family:Verdana;"><sub></sub></span><span style="font-family:Verdana;"></span></i><sub><span style="font-family:Verdana;">0</span><span style="font-family:Verdana;"></span></sub></span><span style="font-family:Verdana;"></span><span style="font-family:Verdana;"> on the flow characteristics such as the flow pattern, size of shock cell, reattachment distance, and velocity and pressure distributions, etc. are examined. The flow pattern was visualized by Schlieren method and the velocity distribution was measured using a Pitot tube. These results will be also useful in understanding the flow characteristics of a gas-atomization annular nozzle approximately.</span></span></span>
基金National Key Research and Development Program of China (No.2018YFB1308801)。
文摘To increase the gripping area of noncontact end grippers(NCEGs), an array-type NCEG based on the Coanda mechanism is proposed, and its performance in gripping different garment fabrics(GFs) is studied. Firstly, the structure and the working mechanism of a single Coanda-based NCEG were analyzed. Secondly, four such grippers were arranged in array to form a minimum gripping unit. Then, the structure of the connecting plate(CP) to the gripper was optimized by simulation analysis to exclude airflow interference, and the adsorption performance of GFs with different fabric parameters was measured. Finally, the experimental results were analyzed to verify the scientific validity and the feasibility of the array-type arrangement. The results show that compared with other NCEGs, the array-type ones based on the Coanda mechanism are better at gripping various large-area GFs and offer better adsorption performance. This innovation provides a new solution to the problem of insufficient gripping area in GF gripping and is very important for improving the production efficiency of garment processing.
基金supported in part by the National Natural Science Foundation of China(NSFC)under grant U1813225,grant 61733014,grant U21B2047,grant U22A2066in part by the Doctorate Foundation of Northwestern Polytechnical University under grant CX201904.
文摘The present study investigated the effect of geometrical and non-geometrical parameters on the thrust performance of a pump-valve propulsion device consisting of a Coanda effect valve(CEV)and a pump.A more accurate theoretical model was also developed to predict the thrust of the pump-valve device.Firstly,a rough thrust model was developed based on existing theory to predict the thrust and energy loss generated by the pump-valve device under different exit and nozzle areas.Considering the limitations of the theoretical analysis,numerical simulations were carried out to evaluate the effect of various geometrical and non-geometrical parameters,including nozzle shape,nozzle area,control port width,exit area,inlet flow rate,etc.,on the thrust performance of the CEV and the pump-valve device.Due to the margin between simulation thrusts and theoretical thrusts,we built an experimental platform and carried out relevant experiments.The experimental data verified the simulation results,and on this basis,the original thrust prediction model was corrected.
基金supports from the National Science and Technology Major Project(J2019-II-0020-0041)the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDA29050000)the National Natural Science Foundation of China(No.51922098).
文摘Gas turbine is a promising device for power generation and propulsion either using traditional or renewable energy fuels.One of its key problems is the flow instability of compressors especially with the increase in blade load and changeable working environment.To intelligently and efficiently inhibit flow separation and enhance the pressure rise ability of highly loaded compressors under variable operating conditions,a novel flow control technique termed as adaptive Coanda jet control(ACJC)is proposed in this paper for a compressor stator cascade with a high diffusion factor of 0.66.To realize the ACJC strategy,an incidence angle(IA)prediction model and an optimal injection mass flow rate(OIMFR)prediction model are established by adopting single factor analysis of variance,principal component analysis and Back Propagation Neural Network(BPNN)methods.Two inlet Mach numbers including 0.1 and 0.4 are considered to represent incompressible and compressible flow conditions,and different inlet incidence angles are involved to model various off-design working situations of the real compressor.Effectiveness of the ACJC system is evaluated using numerical simulations are performed to understand the effects of the injection mass flow ratio on the flow field and aerodynamic performance of the blade cascade.Results indicate that the ACJC system can accurately predict the optimal injection mass flow ratio that can achieve the minimum flow loss at each incidence angle.Compared to the cascade without ACJC under the incidence angel of 5,the optimal injection mass flow ratio being 1.27%and 1.20%can reduce the total pressure loss coefficient by 18.88%and 21.56%for incoming Mach number being 0.1 and 0.4,respectively.
文摘针对无叶风扇气动噪声过大的问题,开展基于CST(Class Function/Shape Function Transformation,CST)参数化方法的柯恩达面气动噪声敏感性分析。首先,以NACA0012翼型及样条曲线构造柯恩达面,建立无叶风扇的风圈截面及三维模型。然后,通过数值模拟分析柯恩达面处的流动情况及气动噪声,并通过试验验证数值计算的准确性。最后,建立柯恩达面参数化模型,并以气动噪声为目标响应,采用Sobol法与Kriging代理模型相结合的方法,计算参数化模型中Bernstein多项式系数的一阶灵敏度系数和总灵敏度系数,找出对气动噪声影响较大的参数。结果表明,影响柯恩达面处气动噪声的主要因素依次为风圈截面的厚度、前缘半径、后缘厚度。
基金supported by the Natural Science Foundation of Jiangxi Province(Nos.20224BAB214061 and 20224ACB214008)the National Natural Science Foundation of China(Nos.52165043 and 52166002)+2 种基金the Jiangxi Provincial Cultivation Program for Academic and Technical Leaders of Major Subjects(No.20225BCJ23008)the Anhui Provincial Natural Science Foundation(No.2308085ME171)the University Synergy Innovation Program of Anhui Province(Nos.GXXT-2023-025 and GXXT-2023-026),China。
文摘Mounds of spatter are generated in laser powder-bed fusion(L-PBF)additive manufacturing,which reduces build quality and laser lifetime.Due to the lack of supplemental airflow above the chamber,the conventional build chamber with a single gas inlet exhibits a pronounced tendency for gas to flow upward near the outlet.This phenomenon results in the formation of a large vortex within the build chamber.The vortex leads to the chaotic motion trajectory of the spatter in the build chamber.The design defects of the existing build chamber based on dual gas inlets are shown in this paper.We established a coupled computational fluid dynamics-discrete phase model(CFD-DPM)model to optimize the build chamber by adjusting the position and structure of the second gas inlet.The homogeneity of the flow is increased with a distance of 379 mm between the two inlets and a wider-reaching second inlet.The Coanda effect is also crucial in the spatter-removal process.The Coanda effect is reduced by modifying the right sidewall of the build chamber and increasing the pressure difference between the inlet and outlet.Finally,we found that the spatter-removal rate rose from 8.9%to 76.1%between the conventional build chamber with a single gas inlet and the optimized build chamber with two gas inlets.
文摘The Coanda effect has long been employed in the aerospace applications to improve the performances of various devices. This effect is the ability of a flow to follow a curved contour without separation and has well been utilized in ejectors where a high speed jet of fluid emerges from a nozzle in the ejector body, follows a curved surface and drags the secondary flow into the ejector. In Coanda ejectors, the secondary flow is dragged in the ejector due to the primary flow momentum. The transfer of momentum from the primary flow to the secondary flow takes place through turbulent mixing and viscous effects. The secondary flow is then dragged by turbulent shear force of the ejector while being mixed with the primary flow by the persistence of a large turbulent intensity throughout the ejector. The performance of a Coanda ejector is studied mainly based on how well it drags the secondary flow and the amount of mixing between the two flows at the ejector exit. The aim of the present study is to investigate the influence of various geometric parameters and pressure ratios on the Coanda ejector performance. The effect of various factors, such as, the pressure ratio, primary nozzle and ejector configurations on the system performance has been evaluated based on a performance parameter defined elsewhere. The performance of the Coanda ejector strongly depends on the primary nozzle configuration and the pressure ratio. The mixing layer growth plays a major role in optimizing the performance of the Coanda ejector as it decides the ratio of secondary mass flow rate to primary mass flow rate and the mixing length.
文摘To control the film thickness of zinc in the process of continuous hot-dip galvanizing, it is known from the early days that the gas wiping through an air knife is the most effective one. The gas wiping using in galvanizing process brings about a problem of splashing from the strip edge for a certain high speed of coating. So, in the present study, the effects of the deflection angle of Coanda nozzle on jet structure and the distribution of impinging pres- sure at the plate surface are investigated numerically and experimentally. In numerical analysis, the governing equations consisted of three-dimensional time dependent full Navier-Stokes equations, standard k-ε turbulence model to solve turbulent stTess and so on are employed. In experiment, 16 channel pressure scanning valve and 3-axis auto traversing unit are used to measure the impinging pressure at the strip surface. As a result, it is found that the smaller the deflection angle for the same nozzle slit of air knife is, the larger the impinging pressure is. To reduce the size of separation bubble and to enhance the cutting ability, it is recommendable to use an air knife with the Coanda nozzle.
文摘Techniques using Coanda effect have been applied to the fiuid control devices. In this field, experimental studies were so far performed for the spiral jet obtained by the Coanda jet issuing from a conical cylinder with an annular slit, thrust vectoring of supersonic Coanda jets and so on. It is important from the viewpoints of effective applications to investigate the characteristics of the supersonic Coanda jet in detail. In the present study the effects of pressure ratios and nozzle configurations on the characteristics of the supersonic Coanda jet have been investigated experhoentally by a schlieren optical method and pressure measurements. Furthermore, Navier-Stokes equations were solved numerically using a 2nd-order TVD finite-volume scheme with a 3rd-rorder three stage Runge-Kutta method for time integration. k - ε model was used in the computations. The effects of initial conditions on Coandaflow were investigated numerically As a result, the simulated flow helds were compared with experimental data in good agreement qualitatively.
基金The authors would greatly thank the supports from the grants of the National Natural Science Foundation of China(Nos.51922098,51790510,and 51636001)the National Major Project of Aeroengine and Gas Turbine(2017-11-0004-0017 and J2019-11-0020-0041).
文摘Coanda jet flap is an effective flow control technique,which offers pressurized high streamwise velocity to eliminate the boundary layer flow separation and increase the aerodynamic loading of compressor blades.Traditionally,there is only single-jet flap on the blade suction side.A novel Coanda double-jet flap configuration combining the front-jet slot near the blade leading edge and the rear-jet slot near the blade trailing edge is proposed and investigated in this paper.The reference highly loaded compressor profile is the Zierke&Deutsch double-circular-arc airfoil with the diffusion factor of 0.66.Firstly,three types of Coanda jet flap configurations including front-jet,rear-jet and the novel double-jet flaps are designed based on the 2D flow fields in the highly loaded compressor blade passage.The Back Propagation Neural Network(BPNN)combined with the genetic algorithm(GA)is adopted to obtain the optimal geometry for each type of Coanda jet flap configuration.Numerical simulations are then performed to understand the effects of the three optimal Coanda jet flaps on the compressor airfoil performance.Results indicate all the three types of Coanda jet flaps effectively improve the aerodynamic performance of the highly loaded airfoil,and the Coanda double-jet flap behaves best in controlling the boundary layer flow separation.At the inlet flow condition with incidence angle of 5°,the total pressure loss coefficient is reduced by 52.5%and the static pressure rise coefficient is increased by 25.7%with Coanda double-jet flap when the normalized jet mass flow ratio of the front jet and the rear jet is equal to 1.5%and 0.5%,respectively.The impacts of geometric parameters and jet mass flow ratios on the airfoil aerodynamic performance are further analyzed.It is observed that the geometric design parameters of Coanda double-jet flap determine airfoil thickness and jet slot position,which plays the key role in supressing flow separation on the airfoil suction side.Furthermore,there exists an optimal combination of front-jet and rear-jet mass flow ratios to achieve the minimum flow loss at each incidence angle of incoming flow.These results indicate that Coanda double-jet flap combining the adjust of jet mass flow rate varying with the incidence angle of incoming flow would be a promising adaptive flow control technique.
基金supported by National Natural Science Foundation of China(No.51276172)National Science and TechnologySupport Project(No.2013BAF05B01)
文摘The unique Coanda surface has a great influence on the performance of bladeless fan.However,there is few studies to explain the relationship between the performance and Coanda surface curvature at present.In order to gain a qualitative understanding of effect of the curvature on the performance of bladeless fan,numerical studies are performed in this paper.Firstly,three-dimensional numerical simulation is done by Fluent software.For the purpose to obtain detailed information of the flow field around the Coanda surface,two-dimensional numerical simulation is also conducted.Five types of Coanda surfaces with different curvature are designed,and the flow behaviour and the performance of them are analyzed and compared with those of the prototype.The analysis indicates that the curvature of Coanda surface is strongly related to blowing performance,It is found that there is an optimal curvature of Coanda surfaces among the studied models.Simulation result shows that there is a special low pressure region.With increasing curvature in Y direction,several low pressure regions gradually enlarged,then begin to merge slowly,and finally form a large area of low pressure.From the analyses of streamlines and velocity angle,it is found that the magnitude of the curvature affects the flow direction and reasonable curvature can induce fluid flow close to the wall.Thus,it leads to that the curvature of the streamlines is consistent with that of Coanda surface.Meanwhile,it also causes the fluid movement towards the most suitable direction.This study will provide useful information to performance improvements of bladeless fans.
