高湍流度格栅的数值模拟及设计方法研究

为探讨高湍流度格栅的几何设计方法,采用基于非结构网格的大涡模拟方法,以单平面格栅为研究对象,计算分析了不同格栅稠度、几何形状、来流雷诺数及表面粗糙度下,格栅后湍流度、各向同性特征沿流向的变化。结果表明,格栅稠度对各向同性湍流度基本无影响,稠度增加能增加格栅初始湍流度;存在优化的格栅形状、与格栅尺寸变化相关的来流雷诺数及格栅表面粗糙度,能改善湍流各向同性特征,进而提高格栅湍流度。

用X型热线探头测量二维变方向和高湍流度流场的新方法

本文分析了以往X热线探头用于测量二维湍流场的局限性,提出了一种能测量主流方向不确定的高湍流度二维湍流场的新方法以及相应的校准新方法,并将这一方法用于斜向自由剪切层的流场测量,经分析,说明该方法测量结果反映了真实流场的特性。

高湍流度格栅下游流场试验研究

为满足高湍流度下涡轮扇形叶栅气动与冷效试验的需求,试制了三种被动控制单平面方形格栅并对其进行了试验验证。对格栅下游流场进行了详细的动态测量,并研究了测量位置、格栅尺寸和来流条件等对格栅下游流场湍流度的影响规律。结果表明,grid 3方案格栅能产生10%以上的湍流度,可作为湍流发生装置并满足后续研究要求;格栅几何特征对其下游湍流度影响显著;在试验范围内,来流速度对湍流度近乎无影响。

高湍流度时全气膜涡轮叶片表面冷却和换热特性的实验研究

为获得高主流湍流度时全气膜涡轮叶片表面的冷却和换热特性,在跨声速风洞中实验研究了质量流量比(MFR)和主流雷诺数(Re)对叶片表面气膜冷却效率和换热系数比的影响。在叶片前缘布置了5排圆形孔,在吸力面和压力面分别布置了3排和6排圆形孔,实验结果由嵌入在叶片中截面的热电偶测得。实验中基于弦长的主流雷诺数的范围为3.0×105~9.0×105,叶栅出口马赫数Ma为0.8,MFR的范围是5.5%~12.5%,主流湍流度Tu为14.7%。实验结果表明:主流雷诺数升高显著增强了叶片表面的换热,使层流边界层到湍流边界层的转捩位置提前。对于吸力面S/C>0.2的区域(S/C为当地弧长与弦长之比),气膜冷却效率受MFR影响明显,当MFR大于7.7%时提高MFR会导致气膜冷却效率降低;该区域的换热系数比在中低雷诺数时受MFR影响较小,在高雷诺数时随MFR升高而升高。压力面S/C<-0.7区域的气膜冷却效率随MFR升高而升高,-0.7<S/C<-0.4区域的气膜冷却效率受MFR影响较小,对于整个压力面而言,MFR升高提高了叶片表面的换热系数。相对于叶片其它区域,压力面后半段区域和吸力面的气膜冷却效率受雷诺数影响较大。

高主流湍流度下大倾角异型气膜孔冷却特性实验研究

为了研究高主流湍流度下大倾斜角异型气膜孔的冷却特性,在主流湍流度为11.82%的流动工况下,采用瞬态液晶传热测量技术对倾斜角均为60°的圆柱孔、水滴孔以及曲面簸箕孔进行了研究。在吹风比为0.5的工况下,3种孔型的气膜贴壁性都较好,上游冷却效率高于下游;在吹风比为1.0的工况下,圆柱孔和水滴孔出现气膜脱离壁面再附着现象,上游冷却效率低于下游;在更大吹风比下,曲面簸箕孔气膜也出现脱离再附着现象。吹风比的增加会显著增强各个气膜孔的对流换热强度,曲面簸箕孔的换热系数比在各个吹风比下都低于圆柱孔和水滴孔,圆柱孔和水滴孔的换热系数比在上游区域较高,而曲面簸箕孔的换热系数比在大吹风比下呈现出先上升后下降的分布特征。实验结果表明,在高主流湍流度条件下,大倾斜角水滴孔和圆柱孔的气膜冷却效果相近,曲面簸箕孔的气膜冷却效果优于这两种孔型。

Flow structure around high-speed train in open air

According to the analysis of the turbulent intensity level around the high-speed train, the maximum turbulent intensity ranges from 0.2 to 0.5 which belongs to high turbulent flow. The flow field distribution law was studied and eight types of flow regions were proposed. They are high pressure with air stagnant region, pressure decreasing with air accelerating region, low pressure with high air flow velocity region I, turbulent region, steady flow region, low pressure with high air flow velocity region II,pressure increasing with air decelerating region and wake region. The analysis of the vortex structure around the train shows that the vortex is mainly induced by structures with complex mutation and large curvature change. The head and rear of train, the underbody structure, the carriage connection section and the wake region are the main vortex generating sources while the train body with even cross-section has rare vortexes. The wake structure development law studied lays foundation for the train drag reduction.

Experimental Investigation on Turbulent Convection in Solar Air Heater Channel Fitted with Delta Winglet Vortex Generator

The paper presents an experimental study on the heat transfer and flow friction characteristics in a solar air heater channel fitted with delta-winglet type vortex generators （DWs）. The experiments are conducted by varying the airflow rate for Reynolds number in the range of 5000 to 24000 in the test section with a uniform heat-flux applied on the upper channel wall. Firstly, the DW pairs are mounted only at the entrance of the lower wall of the test channel （called DW-E） to create multiple vortex flows at the entry. The effect of two transverse pitches （Re= Pt/H= 1 and 2） at three attack angles （a= 30°, 45° and 60°） of the DW-E with its relative height, b/H= 0.5 （half height of channel） is examined. Secondly, the 30° DWs with three different relative heights （blH = 0.3, 0.4 and 0.5） are placed on the upper wall only （absorber plate, called DW-A） of the test channel. The experimental result reveals that in the first case, the 60° DW-E at Rp = 1 provides the highest heat transfer and friction factor while the 30° DW-E at Rp = 1 performs overall better than the others. In the second case, the 30° DW-A at b/H= 0.5 yields the highest heat transfer and friction factor but the best thermal performance is found at b/H = 0.4.

CFD Simulation of Orifice Flow in Orifice-type Liquid Distributor

In this study,a suitable CFD(computational fluid dynamics)model has been developed to investigate the influence of liquid height on the discharge coefficient of the orifice-type liquid distributors.The orifice flow in different diameters and liquid heights has been realized using the shear stress transport(SST)turbulence model and the Gamma Theta transition(GTT)model.In the ANSYS CFX software,two models are used in conjunction with an automatic wall treatment which allows for a smooth shift from a wall function(WF)to a low turbulent-Re near wall formulation(LTRW).The results of the models coupled with LTRW are closer to the experimental results compared with the models with WF,indicating that LTRW is more appropriate for the prediction of boundary layer characteristics of orifice flow.Simulation results show that the flow conditions of orifices change with the variation of liquid height.With respect to the turbulence in orifice,the SST model coupled with LTRW is recommended.However,with respect to the transition to turbulence in orifice with an increase in liquid height,the predictions of GTT model coupled with LTRW are superior to those obtained using other models.

Turbulent Energy Budgets of a Ground Vortex Flow

Turbulent kinetic energy budgets are presented for a highly curved flow generated by the collision of plane wall turbulent jet with a low-velocity boundary layer. The different terms are obtained in the vertical plane of symmetry by quadratic interpolation of the LDV （Laser Doppler Velocimetry） measurements, for a wall jet-to-boundary layer velocity ratio of 2. The results, which have relevance to flows encountered in powered-lift aircraft operating in ground effect, quantify the structure of the complex ground vortex flow. The analysis of turbulent energy equation terms using the measured data revealed that production by normal and shear stresses are both very important to the turbulent structure of the impact zone of the ground vortex. This is an indication that the modeling of turbulence of a ground vortex requires a good representation of the production by normal stresses which is most important in the collision zone.

Profile and Character of Atmospheric Structure Constant of Refractive Index C_n^2

Random fluctuations of turbulence bring random fluctuations of the refractive index, making the atmosphere a random fluctuation medium that destroys the coherence of light-waves. Research in atmospheric turbulence is actually the investigation of the atmospheric refractive index. The atmospheric structure constant of refractive index, C n 2 , is an important parameter denoting atmospheric turbulence. In this paper, C n 2 is measured during the day and at night and in all four seasons using a high sensitivity micro-thermal meter QHTP-2. The vertical profile of C n 2 in Hefei (0-30 km) is investigated by the analysis of experimental data. The average profile of C n 2 in Hefei exhibits conspicuous day and night differences with increased altitude. The distribution of log(C n 2 ) is nearly normal and has conspicuous seasonal differences.

层流叶片在压气机中的应用研究

压气机叶片表面层流流动及转捩现象的捕捉是研究压气机层流叶型的重点和关键。通过基于SST转捩模型的数值方法对某压气机叶型进行数值模拟分析,以精确捕捉普通湍流模型无法捕捉的叶片表面的层流流动及转捩现象,并给定叶片表面转捩的判定依据。在此基础上深入研究低雷诺数环境和高湍流度环境对压气机叶片表面层流流动的影响,验证了在实际压气机环境下,叶片表面的层流流动是可能存在的。为后续压气机层流叶型设计提供数值验证手段和可行性验证基础。

Study on the dynamic characteristics of flow over building cluster at high Reynolds number by large eddy simulation

In this paper,the dynamic characteristics of building clusters are simulated by large eddy simulation at high Reynolds number for both homogeneous and heterogeneous building clusters.To save the computational cost a channel-like flow model is applied to the urban canopy with free slip condition at the upper boundary.The results show that the domain height is an important parameter for correct evaluation of the dynamic characteristics.The domain height must be greater than 8h(h is the average building height)in order to obtain correct roughness height while displacement height and roughness sublayer are less sensitive to the domain height.The Reynolds number effects on the dynamic characteristics and flow patterns are investigated.The turbulence intensity is stronger inside building cluster at high Reynolds number while turbulence intensity is almost unchanged with Reynolds number above the building cluster.Roughness height increases monotonously with Reynolds number by 20%from Re*=103 to Re*=105 but displacement height is almost unchanged.Within the canopy layer of heterogeneous building clusters,flow structures vary between buildings and turbulence is more active at high Reynolds number.

Turbulent hydrodynamics experiments in high energy density plasmas： scientific case and preliminary results of the TurboHEDP project

The physics of compressible turbulence in high energy density(HED) plasmas is an unchartered experimental area.Simulations of compressible and radiative flows relevant for astrophysics rely mainly on subscale parameters. Therefore,we plan to perform turbulent hydrodynamics experiments in HED plasmas(TurboHEDP) in order to improve our understanding of such important phenomena for interest in both communities: laser plasma physics and astrophysics. We will focus on the physics of supernovae remnants which are complex structures subject to fluid instabilities such as the Rayleigh–Taylor and Kelvin–Helmholtz instabilities. The advent of megajoule laser facilities, like the National Ignition Facility and the Laser Megajoule, creates novel opportunities in laboratory astrophysics, as it provides unique platforms to study turbulent mixing flows in HED plasmas. Indeed, the physics requires accelerating targets over larger distances and longer time periods than previously achieved. In a preparatory phase, scaling from experiments at lower laser energies is used to guarantee the performance of future MJ experiments. This subscale experiments allow us to develop experimental skills and numerical tools in this new field of research, and are stepping stones to achieve our objectives on larger laser facilities. We review first in this paper recent advances in high energy density experiments devoted to laboratory astrophysics. Then we describe the necessary steps forward to commission an experimental platform devoted to turbulent hydrodynamics on a megajoule laser facility. Recent novel experimental results acquired on LULI2000, as well as supporting radiative hydrodynamics simulations, are presented. Together with the development of LiF detectors as transformative X-ray diagnostics, these preliminary results are promising on the way to achieve micrometric spatial resolution in turbulent HED physics experiments in the near future.

A three-equation turbulence model for high-speed flows

Adding a new equation to the two-equation K-turbulence model framework,this paper proposed a three-equation turbulence model to determine the density variance for high-speed aero-optics and high-speed compressible turbulent flows.Simulations were performed with the new model for supersonic and hypersonic flat-plate turbulent boundary layer and hypersonic ramp flows.The results showed that the prediction with the present model agrees well with the experimental data and is significantly better than the Lutz's model in predicting the density variance for the flat-plate flows.Furthermore,the present model can produce more accurate skin pressure and skin heat flux distributions than the original K-model in simulating hypersonic compression ramp flows with separation and reattachment and shock/boundary layer interactions.Without introducing a variety of ad hoc wall damping and wall-reflection terms,the proposed three-equation turbulence model is applicable to highspeed aero-optics and turbulent flows of real vehicles of complex configuration.