A novel hybrid method for aerodynamic noise prediction of high-lift devices

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.

Numerical analysis of broadband noise reduction with wavy leading edge

Large Eddy Simulation（LES） is performed to investigate the airfoil broadband noise reduction with wavy leading edge under anisotropic incoming turbulence. The anisotropic incoming turbulence is generated by a rod with a diameter of 10 mm. The incoming flow velocity is 40 m/s and the corresponding Reynolds numbers based on airfoil chord and rod diameter are about 397000 and 26000, respectively. The far-field acoustic field is predicted using an acoustic analogy method which has been validated by the experiment. A straight leading edge airfoil and a wavy leading edge airfoil are simulated. The results show that wavy leading edge increases the airfoil lift and drag whereas the lift and drag fluctuations are substantially reduced. In addition, wavy leading edge can significantly change the flow pattern around the leading edge and a pair of counter-rotating streamwise vortices stemming from each wavy leading edge peak are observed.An averaged noise reduction of 9.5 dB is observed with the wavy leading edge at the azimuthal angle of 90°. Moreover, the wavy leading edge can mitigate noise radiation at all the azimuthal angles without significantly changing the noise directivity. The underlying noise reduction mechanisms are then analyzed in detail.

高速列车排障器气动降噪研究

基于流场恶化理论和声学类比理论建立了一套声学优化设计方法,并应用于高速列车排障器的声学优化设计中。结果表明,头尾车流线体是最重要的声源,分别占总声能的23.7%和33.7%。与尾车流线型部位相比,头车流线型部位声源能量更偏向高频。车体A计权辐射噪声呈现宽频带噪声(主要在1~4 kHz范围内)和峰值特征(尤其在2 kHz)。在四种方案中,最大伸缩长度的排障器能缓和2 k Hz的强峰值效应,降低总声能,并表现出最佳的声辐射性能。通过风洞试验验证了数值计算模型的正确性。

Feedback control of boundary layer Tollmien-Schlichting waves using a simple model-based controller

The attenuation of spatially evolving instability Tollmien-Schlichting(T-S)waves in the boundary layer of a flat plate with zero pressure gradients using an active feedback control scheme is theoretically and numerically investigated.The boundary layer is excited artificially by various perturbations to create a three-dimensional field of instability waves.Arrays of actuators and sensors are distributed locally at the wall surface and connected together via a feedback controller.The key elements of this feedback control are the determination of the dynamic model of the flat plate boundary layer between the actuators and the sensors,and the design of the model-based feedback controller.The dynamic model is established based on the linear stability calculation which simulates the three-dimensional input-output behaviour of the boundary layer.To simplify the control problem,an uncoupled control mode of the dynamic model is made to capture only those dynamics that have greatest influences on the input-output behaviour.A Proportional-Integral-Derivative(PID)controller,i.e.a lead-lag compensator,combining with a standard Smith predictor is designed based on the system stability criterion and the specifications using frequency-response methods.Good performance of the feedback control with the uncoupled control mode is demonstrated by the large reduction of the three-dimensional disturbances in the boundary layer.This simple feedback control is realistic and competitive in a practical implementation of T-S wave cancellation using a limited number of localised sensors and actuators.

Simplified Numerical Models of the Unsteady Tip Leakage Flow in Compressor

Tip leakage flow(TLF)in compressors,which can cause flow blockage in blade passage and induce efficiency loss,is also a potential threat to the unsteady flow stability of modern aeroengines.This paper provides an overview of the significance of tip leakage flow research,and introduces relevant previous studies.After calculating by different methods,large eddy simulation(LES)is demonstrated again as a suitable compromise between accuracy and computational cost for the unsteady flow study.Two types of simplified tip leakage flow models using LES are adopted with a focus on the unsteady characteristics of shedding vortices in a cavity plane.This paper applies these models to study the unsteady tip leakage flow which triggers the onset of acoustic resonance in a multistage axial compressor.Compared with the detected acoustic resonance frequency of 5.22 rotational frequency(RF)in the previous experiment,the computed combination frequency in the 2-D model is equal to 5.232RF,and the simplified 3-D unsteady tip leakage flow model results in a combination frequency of 5.316RF.Therefore,based on the small relative error between model results and experimental results,the simplified numerical models are validated to be sufficiently accurate,and theoretically provide a useful basis for the subsequent research of unsteady tip leakage flow in turbomachinery.

Modification of Flow Structure and Sound Source by Hybrid Porous-serrated Trailing Edge

The effects of hybrid porous-serrated trailing edge on flow structure and sound source of NACA65(12)-10 at moderate Reynolds number(Rec=5×1O^5)have been investigated by Delayed Detached Eddy Simulation(DDES).Compared with conventional serrated trailing edge,the pressure fluctuation in the vicinity of hybrid porous-serrated trailing edge is further decreased significantly.The typical necklace vortex structures stretching across adjacent serrations are suppressed by the porous additive.It is found that porous media changes the shear stress distribution along the serration edge and inside the serration gap,which consequently eliminates the generation of necklace vortex.Therefore,the deformation of vortex tube caused by velocity vector is weakened.The underlying mechanisms associated to the sound source modification are analyzed based on vortex sound theory.The magnitude of Lamb vector and the angle between vorticity and velocity vectors are synchronously reduced by the porous additive,which implies that the present hybrid porous-serrated trailing edge has important influence on the further attenuation of far-field aerodynamic noise.

旋转爆轰波传播模式自发改变过程研究

目的:提出一种预测爆轰波传播模式自发改变的方法。创新点:1.揭示了流场内新爆轰波产生的机制;2.基于接触面化学反应特征时间提出了无量纲参数NL,可作为分析旋转爆轰流场稳定性的判据。方法:以数值模拟为手段,应用基元反应建立化学非平衡流动的数学物理模型,开展旋转爆轰波传播稳定性研究。结论:1.分界面化学反应是引起爆轰波传播模式自发转变的原因之一;2.提出的无量纲参数NL可以将模式转变与爆轰波数联系起来。

A generative deep learning framework for airfoil flow field prediction with sparse data

Deep learning has been probed for the airfoil performance prediction in recent years.Compared with the expensive CFD simulations and wind tunnel experiments,deep learning models can be leveraged to somewhat mitigate such expenses with proper means.Nevertheless,effective training of the data-driven models in deep learning severely hinges on the data in diversity and quantity.In this paper,we present a novel data augmented Generative Adversarial Network(GAN),daGAN,for rapid and accurate flow filed prediction,allowing the adaption to the task with sparse data.The presented approach consists of two modules,pre-training module and fine-tuning module.The pre-training module utilizes a conditional GAN(cGAN)to preliminarily estimate the distribution of the training data.In the fine-tuning module,we propose a novel adversarial architecture with two generators one of which fulfils a promising data augmentation operation,so that the complement data is adequately incorporated to boost the generalization of the model.We use numerical simulation data to verify the generalization of daGAN on airfoils and flow conditions with sparse training data.The results show that daGAN is a promising tool for rapid and accurate evaluation of detailed flow field without the requirement for big training data.