火星盘缝带伞超声速风洞试验结果分析

为了研究盘缝带(DGB)伞在超声速条件下的阻力特性、摆动角以及伞绳载荷分布的不均匀性，在FD 12风洞中开展了盘缝带伞的阻力特性风洞试验，并通过安装柔性传感器测量了伞绳所受载荷。试验结果表明，在Ma1.50到Ma2.50来流条件下，盘缝带伞的阻力系数随着马赫数的增大先增加后减小，在Ma1.75时达到最大，为0.60，而最大摆动角则是先减小后增大，在Ma2.00时摆动角最小，为7.4°，传感器的安装对降落伞风洞试验结果影响很小。通过柔性传感器的标定和误差分析，获取了伞绳载荷数据，结果显示不同伞绳所受拉力的比值可达到1.98。且传感器数据与风洞天平的测量降落伞总载荷结果吻合，进一步验证了柔性传感器结果的正确性。     

Interaction of single-pulse laser energy with bow shock in hypersonic flow

Pressure sensing and schlieren imaging with high resolution and sensitivity are applied to the study of the interaction of single-pulse laser energy with bow shock at Mach 5. An Nd:YAG laser operated at 1.06 lm, 100 mJ pulse energy is used to break down the hypersonic flow in a shock tunnel. Three-dimensional Navier–Stokes equations are solved with an upwind scheme to simulate the interaction. The pressure at the stagnation point on the blunt body is measured and calculated to examine the pressure variation during the interaction. Schlieren imaging is used in conjunction with the calculated density gradients to examine the process of the interaction. The results show that the experimental pressure at the stagnation point on the blunt body and schlieren imaging fit well with the simulation. The pressure at the stagnation point on the blunt body will increase when the transmission shock approaches the blunt body and decrease with the formation of the rarefied wave. Bow shock is deformed during the interaction. Quasi-stationary waves are formed by high rate laser energy deposition to control the bow shock. The pressure and temperature at the stagnation point on the blunt body and the wave drag are reduced to 50%, 75% and 81% respectively according to the simulation. Schlieren imaging has provided important information for the investigation of the mechanism of the interaction.     

侧压式进气道内部阻力的参数分析

为明确高超声速进气道内部阻力的特点,并为进气道减阻设计提供参考依据,以侧压式进气道为例,分别以内壁面和捕获流管为分析体,讨论进气道不同几何设计参数下的阻力特性;以数值模拟为手段,给出了总阻力的大小及各项阻力的分配比例,并分析了进气道几何参数变化对阻力的影响关系。给出了侧压式进气道附加阻力作用表面的形状,讨论了附加阻力的特点。研究发现,内壁面总阻力中,压力阻力随收缩比增加而增加,约占总阻力的60%到70%;唇口前的溢流会产生“附加推力”而不是通常情况的附加阻力。     

A boundary surrogate model for micro/nano grooved surface structure applied in turbulence flow control over airfoil

The application of grooved surface structure is an emerging and effective means in turbulence flow control. However, for a realistic configuration, the global flow field described directly by simple application of massive grids makes it unfeasible to simulate. In this paper, a boundary surrogate model reproducing the effect of microscopic near-wall region is proposed to improve computational efficiency. The surrogate model trained with Lattice Boltzmann Method(LBM) considering the rarefied effec...     

天琴一号卫星加速度模式无拖曳控制

结合卫星加速度模式无拖曳控制系统一般组成、各环节典型模型、常见控制器及天琴一号空间惯性基准建立试验卫星的采样周期与控制周期,着眼于工程实际问题的挖掘与解决,重点阐述了该卫星CIC滤波器组频响特性等效、加速度模式无拖曳控制系统稳定裕度及残余加速度指标分析与综合等技术内容。研究表明,多周期离散系统真实稳定裕度难于准确预测;积分系数是决定PSD指标的关键参数;抗混淆滤波器是提升时域残余加速度指标的关键环节,且有利于抑制高频数据在PSD低中频段的高频折叠;在未引入抗混淆滤波器的情形下,频域指标统计应以进入控制器的残余加速度数据为准。在轨飞行试验结果与仿真结果基本吻合。     

超声速无隔道进气道应用前景的初步研究

随着飞行速度的不断提高,工程中对飞行器包络约束和减阻减重提出了更高的要求,为满足当前工程应用中的迫切需求,以一有隔道进气道为研究背景,对无隔道进气道于超声速领域的应用前景进行初步探索。主要开展了传统和新型两型无隔道进气道的设计研究工作,通过数值计算的方法得到其气动性能和阻力性能的收益变化(传统无隔道进气道在Ma2.2～Ma3.5下总压恢复系数下降5%～7%,额定及超额定状态下减阻约13%～21%;新型无隔道进气道在Ma2.2～Ma3.0总压恢复系数下降2.8%～6.5%,Ma3.5下提升2%,Ma2.2～Ma3.5飞行器减阻约2%～10%),并对其工作机理及流场结构进行了详细的分析,以此给出了工程应用的合理化建议:(1)传统无隔道进气道应选取低马赫数作为设计点,避免其处于亚额定状态工作,以保证获取较好的阻力性能。(2)新型无隔道进气道适用于Ma3量级的超声速领域,具有良好的气动与阻力性能。     

Estimation of sediment settling velocity in estuarine and coastal waters using optical remote sensing data

A robust method has been developed for estimating sediment settling velocity (w_s) from high resolution optical remote sensing data in estuarine, coastal and harbor waters. This method estimates settling velocity as a function of the drag coefficient (C_d), Reynolds number (Re), grain size (D₅₀), specific gravity (Δ_SG) and grain shape (in terms of the Corey Shape Factor – CSF). These parameters were derived from the particulate inherent optical properties such as backscattering (b_bp), beam attenuation (c_p), suspended sediment concentration and turbidity using Landsat 8 OLI and HICO data. Preliminary results for the Gulf of Cambay in the eastern Arabian Sea and Yangtze river estuary in the East China Sea, showed that satellite-retrieved settling velocities (m?s^?1) varied from very low values in clear oceanic waters, intermediate values in coastal waters, to very high values in river plumes and sediment-laden coastal waters. The remote sensing retrievals of sediment properties and their settling velocities were generally consistent with the field and laboratory results, which indicate that the proposed methodology will have important implications in various coastal engineering, environmental and management studies.     

Drag increment induced by a small-scale forward-facing step in Mach number 5 turbulent boundary layer flows

Small-scale roughness elements or imperfections are inevitable over the surface of a flight vehicle. The aerodynamics of these small-scale structures is difficult to predict but may play an important role in the design of a flight vehicle at high speed. The forward-facing step is a typical type of roughness element. Many experiments have been conducted to study the aerodynamics of supersonic forward-facing step, especially with a step height larger than boundary layer thickness. However, few studies focus on small steps. To improve the understanding of small-scale forward-facing step flow, we perform a series of simulations to analyze its aerodynamic influence on a Mach number 5 turbulent boundary layer. The general flow structures are analyzed and discussed. Several shock waves can be induced by the step even if the step height is much smaller than the boundary layer thickness. Two significant shocks are the separation shock and the reattachment shock. The influenced area by the step is limited. With the increase of the step height, the non-dimensional influence area decreases and gradually converges when the step height reaches the boundary layer thickness. There are two normalized distributions of the skin friction coefficient and pressure coefficient associated with step height. By using the normalized parameters, a power-law relationship between the step height and the drag increment coefficient is revealed and fits the simulation results well. It is further illustrated that this relationship still holds when changing the inlet angle of attack, but needs slight modification with the angle of attack.     

Numerical study of a supercritical airfoil/wing with variable-camber technology

Variable-camber technology is considered an effective way to adaptively improve the aerodynamic performance of aircraft under various flight conditions. This paper studies the aerodynamic characteristics of the trailing-edge variable-camber technology by means of Computational Fluid Dynamics (CFD) and a drag decomposition method. Trailing-edge variable-camber technology can be simply realized by the continuous deflection of the flaps and ailerons of a wing. A supercritical airfoil is used to study the two-dimensional effect of variable-camber technology, and a wide-body airplane model is used to validate the three-dimensional improvement in the wing's airfoil made by variable-camber technology. An optimization strategy for airfoil that incorporates variable-camber technology is proposed. The optimization results demonstrate that the proposed method can obtain better results than the traditional segregated shape optimization.