考虑滑流影响的埋入式进气道气动特性分析与流动控制研究

研究滑流对埋入式进气道性能的影响机理对于发动机的稳定性具有重要意义。针对某型涡桨发动机 滑油散热器进排气道系统,基于 CFD技术建立系统的螺旋桨滑流与滑油散热器内流一体化数值模拟方法,进 行考虑滑流影响的滑油散热系统埋入式进气道气动设计仿真分析;针对埋入式进气道由于吸入边界层低能气 流导致通过散热器流量低的问题,设计4组涡流发生器进行主动流动控制。结果表明:滑流使得进气道中的气 流偏离,难以形成稳定漩涡,容易发生流动分离;而合理设计的涡流发生器可以有效改善埋入式进气道内流场 特性,并使通过散热器的流量提高12%。     

Numerical Simulation of Rotor Flow Field Based on Overset Grids and Several Spatial and Temporal Discretization Schemes

A numerical method based on solutions of Euler/Navier-Stokes (N-S) equations is developed for calculating the flow field over a rotor in hover. Jameson central scheme, van Leer flux-vector splitting scheme, advection upwind splitting method (AUSM) scheme, upwind AUSM/van Leer scheme, AUSM+ scheme and AUSMDV scheme are implemented for spatial discretization, and van Albada limiter is also applied. For temporal discretization, both explicit Runge-Kutta method and implicit lower-upper symmetric Gauss-Seidel (LU-SGS) method are attempted. Simultaneously, overset grid technique is adopted. In detail, hole-map method is utilized to identify intergrid boundary points (IGBPs). Furthermore, aimed at identification issue of donor elements, inverse-map method is implemented. Eventually, blade surface pressure distributions derived from numerical simulation are validated compared with experimental data, showing that all the schemes mentioned above have the capability to predict the rotor flow field accurately. At the same time, vorticity contours are illustrated for analysis, and other characteristics are also analyzed.     

Measurements of heat transfer and pressure in a trailing edge cavity of a turbine blade

 An experimental investigation is conducted to obtain the heat transfer and pressure drop data for an integral trailing edge cavity test section that simulates a novel turbine blade's internal cooling passage with bleed holes. Local heat transfer is measured on both the suction and pressure sides by a transient liquid crystal technique, while pressures at six positions are recorded by pressure calibrators. Moreover, flow characteristic and its effect on heat transfer are analyzed for conditions with or without bleed flow. The experimental results show that, in the cases with bleed flow, local heat transfer on the pressure side exceeds that on the suction side in the first and second channels. In the cases without bleed flow, in the first and third channels, local heat transfer on the suction side weakens whilst it increases significantly on the pressure side. For the second channel, non-bleed condition leads to a more balanced heat transfer distribution between the upstream and downstream channel. Besides, after the bleed holes are blocked, heat transfer in the first bend region on the suction side declines sharply, while the opposite phenomenon occurs for the second bend region on the pressure side. In both bleed and non-bleed cases, the total pressure of six measurement positions decreases continuously along the channel at the same Reynolds number and it promotes for higher Reynolds number. Among all the measurement points, under the same flow rate condition, the highest speed occurs at Position 5, which also shows the maximum difference between the total and static pressures. When the bleed holes are blocked, the total pressure at each measurement position appears to increase.     

RELATIONSHIPS FOR MOTION DESCRIBED IN ANY TWO ROTATIONAL REFERENCE FRAMES

In this paper the definitions of the relative derivatives of a vector with respect to time in any reference frame by using the notation of vectrix are proposed. It is further shown that with the help of vectrix one can treat the relative derivatives more clearly and more rigorously when multiple reference frames are concerned. Very useful relationships between the first order relative derivatives described in any two reference frames are derived. Relationships for the second order relative derivatives are also presented in detail. A new concept called "rotation induced acceleration" which is caused by the rotation of two reference frames when motion is necessarily described in them is presented. The result obtained in this paper is the generalization of the acceleration theorem given in conventional theoretical mechanics.     

Structure and kinetic properties of slow-mode shocks associated with magnetic reconnection in the near-Earth magnetotail

We study the structure and kinetic properties of slow-mode shocks near the plasma sheet boundary layer (PSBL) associated with magnetic reconnection by Cluster observation. The presence of slow-mode shocks is confirmed by traditional Rankine–Hugoniot (RH) analysis and Monte-Carlo shock fitting method. The Walén analysis, applied to the tailward flow associated with slow-mode shocks, also supports that plasma was accelerated across a Petschek-type slow-mode shock connected to the diffusion region. Back-streaming ions were observed on the shock layer, and cold ions were accelerated and heated by slow-mode shocks. In addition, whistler and electrostatic solitary waves were observed around the slow-mode shocks. These waves might be excited by the observed field-aligned electron beams near the shocks.     

可压缩流动激波装配在格心型有限体积法中的应用

发展了一种基于格心型有限体积方法(FVM)的激波装配算法。通过定义网格节点属性可以灵活调用激波装配和激波捕捉计算方法。在使用激波装配方法时,激波节点运动速度和下游运动速度通过Rankine-Hugoniot(R-H)关系式获得,同时采用非结构动网格技术描述激波的运动以及调整其他网格节点的位置。流过激波面元的通量为上游单元的基本通量,物理概念更加清晰,通量计算也更为准确。在计算过程中,网格节点属性可以发生变化,以此实现对带有拓扑变化流场的描述。数值试验表明:本文提出的计算方法不但具有较高的计算精度,同时能有效地避免由于捕捉激波而出现的数值问题。     

二维三角晶格的Peierls相变前后的声子色散曲面的研究

利用晶格动力学理论计算了二维三角晶格的Peierls相变前后的声子能谱。并且在第一布里渊区绘制了声子色散曲面。通过对Peierls相变前后的声子能谱比较可知，随其对称性降低，声子能谱的简并度被破缺。二维三角晶格的Peierls相变前只有两支声频支声子能谱，Peierls相变后有两支声频支声子能谱与两支光频支声子能谱，并且声频支声子能谱与光频支声子能谱不相交，两支光频支声子沿ky轴平缓地变化。     

Dynamics of a spacecraft and normalization around Lagrangian points in the Neptune–Triton system

The problem of a spacecraft orbiting the Neptune–Triton system is presented. The new ingredients in this restricted three body problem are the Neptune oblateness and the high inclined and retrograde motion of Triton. First we present some interesting simulations showing the role played by the oblateness on a Neptune’s satellite, disturbed by Triton. We also give an extensive numerical exploration in the case when the spacecraft orbits Triton, considering Sun, Neptune and its planetary oblateness as disturbers. In the plane a × I (a = semi-major axis, I = inclination), we give a plot of the stable regions where the massless body can survive for thousand of years. Retrograde and direct orbits were considered and as usual, the region of stability is much more significant for the case of direct orbit of the spacecraft (Triton’s orbit is retrograde). Next we explore the dynamics in a vicinity of the Lagrangian points. The Birkhoff normalization is constructed around L₂, followed by its reduction to the center manifold. In this reduced dynamics, a convenient Poincaré section shows the interplay of the Lyapunov and halo periodic orbits, Lissajous and quasi-halo tori as well as the stable and unstable manifolds of the planar Lyapunov orbit. To show the effect of the oblateness, the planar Lyapunov family emanating from the Lagrangian points and three-dimensional halo orbits are obtained by the numerical continuation method.     

Numerical prediction and wind tunnel experiment for a pitching unmanned combat air vehicle

The low-speed flowfield for a generic unmanned combat air vehicle (UCAV) is investigated both experimentally and numerically. A wind tunnel experiment was conducted with the Boeing 1301 UCAV at a variety of angles of attack up to 70 degrees, both statically and with various frequencies of pitch oscillation (0.5, 1.0, and 2.0 Hz). In addition, pitching was performed about three longitudinal locations on the configuration (the nose, 35% MAC, and the tail). Solutions to the unsteady, laminar, compressible Navier–Stokes equations were obtained on an unstructured mesh to match results from the static and dynamic experiments. The computational results are compared with experimental results for both static and pitching cases. Details about the flowfield, including vortex formation and interaction, are shown and discussed, including the non-linear aerodynamic characteristics of the vehicle.     

基于图剖分的多块结构网格负载平衡方法

负载平衡是影响并行计算性能的重要因素。针对多块结构网格,给出了一种改进的多层次图剖分负载平衡方法。该方法设计了新的网格剖分算法,采用改进的子块分裂方法与图剖分算法的循环调用实现结构对接网格剖分,并通过建立不同物体重叠网格间的连接关系,实现了结构重叠网格的负载平衡。采用2个典型算例对方法进行了对比验证,数值结果表明,子块分裂方法对剖分结果具有重要影响,采用循环调用算法及改进的子块分裂方法能有效地实现计算负载均衡及通信量优化,同时显著减少了网格块数及因虚网格导致的内存需求,有利于提高并行效率。该负载平衡方法与网格拓扑无关,适用于多块结构对接网格及重叠网格,且整体型剖分方式对于多块结构重叠网格具有更好的剖分效果。