Effects of surface roughness on the aerodynamic performance of a high subsonic compressor airfoil at low Reynolds number

The aerodynamic performance of compressor airfoil is significantly affected by the surface roughness at low Reynolds number (Re). In the present study, numerical simulations have been conducted to investigate the impact of surface roughness on the profile loss of a high subsonic compressor airfoil at Re = 1.5 × 10⁵. Four roughness locations, covering 10%, 30%, 50% and 100% of the suction surface from the leading edge and seven roughness magnitudes (R_a) ranging from 52 to 525 μm were selected. Results showed that the surface roughness mainly determined the loss generation process by influencing the structure of the Laminar Separation Bubble (LSB) and the turbulence level near the wall. For all the roughness locations, the variation trend for the profile loss with the roughness magnitude was similar. In the transitionally rough region, the negative displacement effect of the LSB was suppressed with the increase of roughness magnitude, leading to a maximum decrease of 14.6%, 16.04%, 16.45% and 10.20% in the profile loss at R_a = 157 μm for the four roughness locations, respectively. However, with a further increase of the roughness magnitude in the fully rough region, the stronger turbulent dissipation enhanced the growth rate of the turbulent boundary layer and increased the profile loss instead. By comparison, the leading edge roughness played a dominant role in the boundary layer development and performance variation. To take fully advantage of the surface roughness reducing profile loss at low Re, the effects of roughness on suppressing LSB and inducing strong turbulent dissipation should be balanced effectively.     

高速大攻角Re数效应试验与分析

采用两个尺度不同的某战斗机模型,在2.4m高速风洞中进行了大攻角Re数效应试验研究。试验攻角范围为0°~70°,基于前机身端部当量直径的ReD=0.42×106~2.27×106。试验结果表明,Re数对大攻角试验数据影响明显;表面微几何效应、M数同样对大攻角气动特性也有一定影响;模型头部贴“八”字形粗糙带可以减弱Re数的影响,却不能获得高Re数下的试验结果。     

波动方程差分解法及其对矩形波导双T形接头的分析

对波动方程差分解法进行了研究 ,给出了电场的计算公式 ,将上述方法应用于矩形波导双T形接头的分析 ,得到了与实测相吻合的各端口反射系数值。     

TiBw/TA15复合材料板材超塑变形行为研究

研究了TiB_w/TA15复合材料板材在900～960℃、5×10^–4～10^–2s^–1条件下的超塑变形行为。结果表明,TiB_w/TA15复合材料流变应力随拉伸温度的升高和应变速率的减小而降低,在940℃、5×10^–3s^–1变形条件下获得的最大超塑性伸长率为439%。利用Zener–Hollomn参数和Arrhenius方程所建立的峰值应力本构方程为ε~·=3.55×10⁸[sinh(2.0×10^–2σ)]^1.99×exp(–6.381×10⁵/RT),其变形激活能Q=638.1kJ/mol。复合材料超塑性变形组织与拉伸温度和应变速率密切相关。高温低应变速率有利于基体α相的动态再结晶以及晶须与基体处孔洞的愈合,低温高应变速率下,孔洞更易萌生于增强相与基体结合界面的端部。动态再结晶对复合材料超塑性的发挥起着关键作用。     

进气道俯仰振荡状态的非定常数值仿真

为研究进气道俯仰振荡状态时的性能,耦合求解俯仰振荡运动和非定常Navier-Stokes方程,对平衡攻角为0°、振荡幅值为15°的进气道非定常流场进行了数值仿真。结果表明：在俯仰振荡状态下,进气道的性能发生周期性变化,存在一个类似于领结形状的滞环。     

Inverse design of low boom configurations using proper orthogonal decomposition and augmented Burgers equation

Mitigation of sonic boom to an acceptable stage is a key point for the next generation of supersonic transports. Meanwhile, designing a supersonic aircraft with an ideal ground signature is always the focus of research on sonic boom reduction. This paper presents an inverse design approach to optimize the near-field signature of an aircraft, making it close to the shaped ideal ground signature after the propagation in the atmosphere. Using the Proper Orthogonal Decomposition(POD) method, a guessed input of augmented Burgers equation is inversely achieved. By multiple POD iterations, the guessed ground signatures successively approach the target ground signature until the convergence criteria is reached. Finally, the corresponding equivalent area distribution is calculated from the optimal near-field signature through the classical Whitham F-function theory. To validate this method, an optimization example of Lockheed Martin 1021 is demonstrated. The modified configuration has a fully shaped ground signature and achieves a drop of perceived loudness by 7.94 PLdB. This improvement is achieved via shaping the original near-field signature into wiggles and damping it by atmospheric attenuation. At last, a nonphysical ground signature is set as the target to test the robustness of this inverse design method and shows that this method is robust enough for various inputs.     

Solitary and periodic waves in magneto–rotating plasmas: Effect of the Kappa–Cairns distributed electrons

The nonlinear propagation of ion–acoustic (IA) waves in a magneto–rotating plasma is studied by considering the Kappa-Cairns electron distribution. Employing the perturbation scheme, Korteweg–de Vries equation is derived. It is seen that both positive and negative potential solitons can be supported in the present plasma model. The numerical results reveal that the Kappa-Cairns distributed electrons modify features of the electrostatic waves significantly. The effects of non–thermal parameters, plasma rotation frequency, ion temperature, and the wave propagation angle on electrostatic solitary wave structures are also discussed here. It is found that the plasma parameters considerably influence the propagation of IA waves in rotating plasmas. Furthermore, using the bifurcation theory of planar dynamical systems to the K-dV equation, we have presented the existence of solitary and periodic traveling waves. Our study may be helpful to understand the behavior of ion–acoustic wave in the rotating plasma.     

基于目标加速度方向观测的微分对策制导律

针对延迟信息条件下的机动目标拦截问题,研究了一种考虑目标加速度方向观测的微分对策制导律。首先,针对引入目标方向观测信息末制导博弈问题,建立了微分对策数学模型。随后,利用状态依赖黎卡提方程求解微分对策问题,得到包含无延迟目标机动项的微分对策制导律,可以更为有效地拦截机动目标。最后,在延迟信息条件下,利用目标加速度方向观测的方法补偿延迟的目标加速度,再将补偿后的目标加速度信息取代无延迟的目标加速度,得到延迟信息条件下考虑目标加速度方向观测的微分对策制导律。仿真结果表明,新的制导律可以在延迟信息条件下有效地拦截机动目标。     

Numerical investigation of transitions in flow states and variation in aerodynamic forces for flow around square cylinders arranged inline

This study focuses on the transitions in flow states around two-, three- and four-inline square cylinders under the effect of Reynolds numbers at two different gap spacing values using the lattice Boltzmann method. For this purpose, Reynolds number is varied in the range 1–130 while two different values of spacing taken into account are gap spacing?=?2 and 5. Before going to actual problem, the code is tested for flow around a single square cylinder by comparing the results with experimental and numerical results of other researchers, and good agreement is found. The current numerical computations yield that for both spacing values and all combinations of cylinders there exist three different sates of flow depending on Reynolds numbers: steady state, transitional state and unsteady state. It is found that the range of Reynolds numbers for these flow states is different for both spacing values. At gap spacing?=?2 the range of Reynolds numbers for each flow state decreases by increasing the number of cylinders while at gap spacing?=?5 opposite trend is observed. The results also show that at gap spacing?=?2 the reduction in drag force is greater than the corresponding reduction at gap spacing?=?5. The maximum reduction in drag force is observed at Reynolds numbers?=?1 at both spacing values. Similarly, at both spacing values and all Reynolds numbers, the maximum reduction in drag force is observed for the case of four-inline square cylinders.     

Positron nonextensivity contributions on the rational solitonic,periodic, dissipative structures for MKP equation described critical plasmas

New closed forms have been exposed that rational, trigonometric, periodical, explosive, hyperbolic and shock solutions can be usable in the ionosphere plasma of earth. To explore the nonextensive impacts on the features of nonlinear waves in this plasma model, using Riccati-Bernoulli sub-ODE process, the MKP equation has been solved. This method is very important in the study of dynamics and motion in fluids. Some of the obtained new potential solutions are prefect achievements in plasma observations and applications in ionosphere.