Visualization of coherent structures in a supersonic flat-plate boundary layer

Flow in a flat-plate zero-pressure-gradient boundary layer at Mach 3 was visualized via nanoparticle-based planar laser scattering (NPLS). Coherent structures such as an individual hairpin vortex and hairpin packet were identified in the streamwise-wall-normal plane on the basis of the now accepted hairpin model. Λ-shaped vortices were found in a staggered pattern in the stream-wise-spanwise plane, which indicated H-type transition in the present experiments. This is the direct evidence (in the form of flow...     

An experimental study on fine structures of supersonic laminar/turbulent flow over a backward-facing step based on NPLS

Fine structures of supersonic flow over a 5 mm high backward facing step(BFS),including expansion wave fan,reattachment shock,supersonic boundary layer were measured in a Ma=3.0 low-noise indraft wind tunnel.By varying the superficial roughness of the wall upstream from the step,supersonic laminar flow and supersonic turbulent flow could be formed over a BFS.Measurements on the spatiotemporal features of the holistic flow field and the fine structures in four typical regions were carried out using NPLS(nano-based planar laser scattering).Flow structures,including expansion wave fan,reattachment shock,supersonic boundary layer and its separation,reattachment and redevelopment are revealed by measuring the holistic structure of the transient flow field.Comparing the two time-averaged flow fields with each other,it is apparent that supersonic turbulent flow over a BFS(STF-BFS) has a larger expansion angle and a shorter recirculation region,and its redeveloped boundary layer increases at a smaller obliquity while the angle of reattachment shock is the same for the supersonic laminar flow over a BFS(SLF-BFS).With regard to time-evolution features,the K-H vortices in the SLF-BFS suffers from shearing,expansion,reattachment and three-dimensional effects while in the STF-BFS large-scale structures are affected by the incline and distortion at the reattachment point due to expansion,viscosity and reverse-pressure.Studies on local regions indicate that in the SLF-BFS,the emergence of compression waves which distinctly converge into a reattachment shock is due to the local convective Mach number and the inducement of K-H vortices in the free shear layer.Nevertheless,in the STF-BFS,compression waves and K-H vortices are barely evident,and the formation of a reattachment shock is related to the wall compressive effect.     

The experimental study of interaction between shock wave and turbulence

The interaction between shock wave and turbulence has been studied in supersonic turbulent mix layer wind tunnel. The interaction between oblique shock wave and turbulent boundary layer and the influence of large vortex in mix layer on oblique shock wave have been observed by NPLS technique. From NPLS image, not only complex flow structure is observed but also time-dependent supersonic flow visualization is realized. The mechanism of interaction between shock wave and turbulence is discussed based on high quality NPLS image.     

Aero-optical aberration measuring method based on NPLS and its application

The existing methods for measuring aero-optical aberration suffer from several problems, such as low spatiotemporal resolution, sensitivity to environment, and integral effects. A new method for measuring aero-optical aberration of supersonic flow is proposed. Based on the self-developed measuring method of supersonic density field, the wavefront aberration induced by a cross-section of supersonic flow field could be measured by ray-tracing. Compared with other methods, the present one has three significant innovations: (1) high spatiotemporal resolution. Its time resolution is 6 ns, and the spatial resolution can reach up to micrometers; (2) it can avoid the integral effects and study the wavefront aberration induced by the flow field of interest locally; (3) it can also avoid the influence from the test section wall boundary layers and environmental disturbances. The present method was applied to supersonic flow around an optical bow cap. The results of high spatiotemporal resolution reveal fine wavefront structures, and show that shock waves, expansion waves and turbulent boundary layers have different impacts on the wavefront aberration.     

离心式压缩机无叶扩压器内三元紊流附面层的计算

提出了一种计算无叶扩压器两壁面上不可压缩三元紊流附面层的方法。分析中假设径向速度剖面为二阶梯形,且附面层内的速度分布采用能明显表示主流流线偏转角影响的Johns ton的三角形模型。将附面层的动量积分方程与主流的关系式联立起来求解。计算出的无叶扩压器的气动特性与作者的试验结果吻合良好。     

不同飞行高度下超声速来流/射流及其相互作用的数值模拟

采用高精度格式求解二维Navier-Stokes方程,研究了不同飞行高度下超声速来流和射流在后台阶相互作用的流场基本结构.时间推进采用三阶精度Runge-Kutta格式,分别应用五阶精度加权本质无振荡(weighted essentially non-oscillatory,WENO)格式、六阶精度中心差分格式来离散对...     

超音速风洞扩压器激波串现象的数值模拟

超音速扩压器性能研究具有非常重要的工程实际应用价值。该文为加深对超音速风洞扩压器内流场结构的理解,采用Fluent软件对“收缩段等直段扩张段”型扩压器流场进行了数值计算,较好模拟了扩压器中由激波/边界层干扰诱导的复杂流场的流场特性,再现了流场中的“激波串”和“伪激波”现象,与文献结果吻合较好。并以比较精细的二维网格计算结果对激波串的形成机理和典型流动结构进行了分析,同时应用于实际工程,对某超音速风洞扩压器不同二喉道长度状态下的扩压效率进行了比较。     

磁流体流动控制在航空工程中的应用与发展

总结了国内外磁流体(MHD)流动控制的研究现状,重点介绍了磁流体流动控制的3个典型实验:调节超音速进气道激波系结构,抑制流体边界层分离,减弱诱导激波强度;对磁流体流动控制机理进行了初步分析,说明放电等离子体能在激励区产生高温等离子体层,由于局部气体高温高压诱导出激波,形成虚拟尖劈,从而改变原有流场结构,施加磁场的主要用途是对放电电弧施加宏观的洛仑兹体积力,控制电弧运动的方向.最后,总结了磁流体流动控制的优势,并对国内MHD流动控制在航空工程上的应用与发展进行了展望.     

A new compressibility modification <Emphasis Type="Italic">k</Emphasis>-ε turbulence model with shock unsteadiness effect

A new compressibility modification k-ε model, including shock unsteadiness effect and the previous compressibility modification of pressure dilatation and dilatational dissipation rate, was developed with a simple formulation for numerical simulation in supersonic complex turbulent flows. The shock unsteadiness effect was modeled by inhibiting turbulent kinetic energy production in the governing equations of turbulent kinetic energy and the turbulent kinetic energy dissipation rate. Sarkar＇s correction models were employed accounting for the dilatational compressibility effects in the new model. Two types of flows, the free supersonic mixing layers and complex supersonic flow with transverse injection were simulated with different flow conditions. Comparisons with experimental data of the free supersonic mixing layers showed that the new compressibility modification k-ε model significantly inhibited the excessive growth of turbulent kinetic energy and improved predictions. On the supersonic mixing layer flows, prediction results with the new model were in close agreement with experimental data, accurately predicting the decreasing trend of the mixing layer spreading rate with the increase of the convective Mach number. Due to the complicated flow field with flow separation, shock unsteadi- ness modification inhibited excessive growth of the turbulent kinetic energy in shock regions and wider shock regions are predicted, thereby significantly improving results of the flow with a strong separation forecast. The flow separation was stronger, which was the primary modification effect of the new model. Predictions accord with experimental results even in strong separation flows.     

车身非光滑表面边界层流场特性分析

为了研究非光滑车身表面边界层流场特性,采用大涡模拟与Realizable k-ε湍流模型对车身外部瞬态和稳态流场进行数值模拟计算,对比分析了非光滑模型与光滑模型边界层内速度、粘性底层厚度、壁面剪切力、表面摩擦阻力因数、湍流强度和湍流耗散率等流场参数,解析了非光滑表面对车身流场流动特性的影响.研究结果表明,非光滑模型边界层内速度明显高于光滑模型,边界层厚度、壁面剪切力、表面摩擦阻力因数、湍流强度、湍流耗散率都比光滑模型有所减小.非光滑表面的引入加剧了车身尾迹气流的参混效应,防止外界的高速流对内部低速流的引射作用,从而减少了车身流场能量的损失.     

Experimental investigation on upstream-injection interaction with a scramjet cavity flameholder

The study has evaluated the coherent structures and the velocity field of gaseous transverse jet upstream of a scramjet flameholder in a supersonic turbulent flow. The high spatiotemporal resolution coherent structures of the jet plume/wakes and the cavity shear layer were obtained by utilizing the nanoparticle-based planar laser scattering technique. Compared to the no upstream injection case, the cavity shear layer downstream of the jet shows significant mass exchange with mainstream. The particle image veloc- imetry velocity field and the velocity profiles demonstrated that the interaction intensity of the cavity shear layer with the upstream injection is further enhanced as the injection stagnation pressure increases.     

一类线性双曲型方程Goursat问题的能量估计

在位势流模型下,研究了超音速气流过二维斜坡的弱激波解的存在唯一性.该问题的关键是证明其相应线性问题的先验能量估计.先通过部分速度图变换,将拟线性双曲方程的自由边值问题化简为固定边值问题,然后通过待定系数法,选择适当的积分因子,进行分部积分,结合问题本身的边界条件,获得了相应线性Goursat问题的能量估计.从而用相对简单的方法获得了与文献[1-2]类似的结果.     

Effect of Mach number on transonic flow past a circular cylinder

The effect of Mach number on transonic flow past a circular cylinder is investigated numerically for the free-stream Mach number M∞ from 0.85 to 0.98 and the Reynolds number 2×10^5 based on the diameter of the cylinder. The work provides an insight into several salient features, including unsteady and quasi-steady flow state, formation of local supersonic zone, and evolution of turbulent shear layer. Results show that there exist two flow states dependent of a critical Mach number Mcr around 0.9. One is an unsteady flow state characterized by moving shock waves interacting with the turbulent flow in the near region of the cylinder for M∞〈Mcr, and the other is a quasi-steady flow state with nearly stationary shock waves formed in the near wake for M∞〉Mcrs, suppressing vortex shedding from the cylin- der. Some flow behaviors in the unsteady and quasi-steady flow states are revealed. From time evolu- tion of flow structures, local supersonic zones are identified in the wake and generated by two typical processes, i.e. reverse flow behind the cylinder and shed vortices in the near wake. The convective Mach number Mc of turbulent shear layers shed from the cylinder is identified nearly as Mc〈I in the unsteady flow regime and Mc〉I in the quasi-steady flow regime, resulting in different evolutions of the shear layers.     

脉动流对壁面边界层流动的数值研究

为了研究非稳态尾迹对平板表面流动和换热的影响,本文将非稳态尾迹引起的主流速度脉动简化为正弦变化,通过数值的方法研究了脉动频率和振幅对平板壁面边界层流动和换热的影响,研究结果表明:边界层内的速度、壁面温度、壁面摩擦系数和平均换热系数随着时间的变化做周期性脉动;边界层内流动与主流之间存在着相位差,壁面距离越小,相位差越大;边界层内的速度和壁面摩擦系数脉动幅度的大小与主流脉动频率和振幅成正比;壁面温度和壁面平均换热系数的波动大小与主流脉动频率成反比,与脉动振幅成正比,当主流脉动频率和脉动振幅增加到一定值后,靠近壁面的地方出现回流,回流强度与脉动频率和振幅成正比。     

投弃式海流剖面仪探头流场数值模拟

 以三维Navier-Stokes方程为控制方程,结合k-ε两方程湍流模型,采用隐式有限体积法对投弃式海洋剖面仪（XCP）探头进行数值模拟,分析XCP探头周围流场的分布情况。根据XCP探头周围流场分布,对探头的运动特性,重点是探头的头部和尾翼流场进行分析。研究表明,在探头迎流前端小于10cm处,流体层流边界层发展为湍流边界层,因此探头头部的弧线型设计对于保证探头获得稳定的下落速度作用至关重要,探头尾翼虽然会减小下落速度,但有利于保证探头稳定的垂直下落姿态。研究结果验证了模拟计算方法的准确性,同时为同类探头的优化设计提供了参考依据。     

超声速旋流天然气分离器的旋流特性数值模拟

与传统的低温分离工艺相比，超声速旋流天然气分离器是天然气处理工艺技术的一大创新。在超声速旋流天然气分离器中，气流经过拉伐尔喷管绝热膨胀形成带液滴的超声速低温混合气流，在超声速翼的作用下混合气流由轴流转换成旋流，实现超声速旋流分离。超声速翼是实现气液分离的关键部件。设计了三角薄板型超声速翼，并利用CFD软件对超声速翼段内气流温度、压力、马赫数等特性参数的变化规律和翼段沿主流方向切向速度的变化情况进行了分析。结果表明，在所设计的超声速翼段内，气流能始终保持超声速，翼段出口马赫数为1．4，翼前无激波产生；分离器的旋流加速度最高在572000g，可实现良好的超声速气液旋流分离。     

跨音速下旋成体干扰流场计算

应用粘性-无粘性干扰方法计算了亚跨音速下旋成体的轴对称绕流流场,并着重研究了船尾处的后体流场.将流场划分为无粘的位流区和粘性影响集中的边界层区,利用有限差分法和积分关系式法分别求解之后,以边界层位移厚度为粘性匹配条件进行耦合计算,求出弹身表面的压力分布.该方法可直接用于计算导弹燃气喷流产生的“阻塞”效应对船尾-后体流场的影响。     

流体边界层对低渗透油藏渗流特征的影响

 低渗透油藏孔喉细小、孔隙结构复杂,固液界面相互作用力很大,在靠近孔喉壁面处存在一层流体边界层,阻碍流体在孔喉中的流动。为研究流体边界层对低渗透油藏流体渗流特征的影响,以去离子水在半径分别为10.0,7.5和5.0μm的微圆管中流动的实验数据为基础,通过数据拟合分析,确定了流体流动速度、边界层厚度与压力梯度之间的关系。结果表明,由于流体边界层的存在,低压条件下,去离子水在不同半径微圆管中的流动偏离经典的达西流动规律,表现出非线性特征,且存在启动压力梯度;随着管径的降低,流动偏离达西渗流规律的程度增大,非线性越发明显;随压力梯度增加,流体边界层厚度呈指数规律递减,压力增大到一定程度后,趋于定值。运用不等径毛管束模型,给出低渗透油藏单相流体渗流公式。     

三维多层流动过孤立山脉产生的山脉重力波的数值试验

利用中尺度数值模式ARPS研究了分层流动大气中的非线性山脉重力波。分层流动过孤立山脉所产生的山脉重力波的数值模拟表明,具有两层模式结构的气流过孤立山脉产生一个发散模态的拦截背风波,同线性理论模式计算结果具有基本相同的流动特征。但是具有三层模式结构的气流过孤立山脉所产生的非线性山脉重力波和大气船波表现出同两层模式结构的气流完全不同的流动特征,因非线性相互作用在山脉背风面产生了2个发散波模态的拦截背风波向山脉下游传播,具有同两层模式和线性理论模式相比更加复杂的波动特征。     

高超声速流动中双尺度湍流模式的应用

论文研究了双尺度湍流模式,并对其在壁面附的近长度尺度进行了修正,选择四个基准流动－超声速和高超声速二维压缩拐角,锥柱裙组合体绕流和斜激波／平板湍流边界层干扰－进行了数据计算,数值计算和实验结果的比较表明修正双尺度湍流模式对流动分离,摩阻和热流的计算具有更好的效果。