Experimental and Numerical Investigation of the Effects of Passive Vortex Generators on Aludra UAV Performance

A study of the effects of passive vortex generators (VGs) on Aludra unmanned aerial vehicle (UAV) aerodynamic characteristics is presented. Both experimental and numerical works are carried out where an array of VGs is attached on Aludra UAV’s wing. The flow measurements are made at various angles of attack by using 3-axis component balance system. In the numerical investigation, the Reynolds-averaged Navier-Stokes (RANS) code FLUENT 6.3TM is used in the simulations with fully structured mesh with Spalart-Allmaras (S-A) turbulence model and standard wall function. The comparison between the experimental and numerical results reveals a satisfactory agreement. The parametric study shows that higher maximum lift coefficient is achieved when the VGs are placed nearer to the separation point. In addition to this, shorter spanwise distance between the VGs also increases the maximum lift coefficient, rectangular and curve-edge VG performs better than triangular VG.     

环下润滑结构内部流动分析和收油叶片结构优化研究

为了研究环下润滑结构内部流动并优化收油叶片结构,根据环下润滑结构内部高转速、强旋流的流动特点建立了数值计算模型,分析了原始结构的油气两相流动并总结了滑油的损失机理,在此基础上提出收油叶片的优化改进结构,详细讨论了不同收油叶片结构对环下润滑内部流动和收油效率的影响规律。研究结果表明,原始结构中滑油冲击主轴产生的碰撞飞溅和在离心作用下沿收油叶片被向外甩出均是引起收油效率下降的原因;优化收油叶片结构后的气流速度在叶尖附近的最大增加幅度不超过4m/s;收油叶片叶根拐角处采用圆弧过渡且叶根延伸后的收油效率仅在低转速范围内略高于原始结构的收油效率,收油效率最大提升了1.03%;在此基础上增加阶梯结构并进一步延伸叶根后可在全部转速范围内提升收油效率,相对原始结构的收油效率最大可提升接近5.0%。     

CFD在舰船甲板流场计算与特性研究中的应用

本文通过运用CFD技术数值模拟舰船的运动,来求解各种舰桥风速和风向下的甲板流场。建立了某型舰船的物理模型和外流场网格,给出了甲板流场的结果矢量图,并与试验结果进行对比分析,得出流场规律,为直升机在甲板上的安全起降提供技术支持。     

Flow field and pressure loss analysis of junction and its structure optimization of aircraft hydraulic pipe system

The flow field in junction is complicated due to the ripple property of oil flow velocity and different frequencies of two pumps in aircraft. In this study, the flow fields of T-junction and Y-junction were analyzed using shear stress transport (SST) model in ANSYS/CFX software. The simulation results identified the variation rule of velocity peak in T-junction with different frequencies and phase-differences, meanwhile, the eddy and velocity shock existed in the corner of the T-junction, and the limit working state was obtained. Although the eddy disappeared in Y-junction, the velocity shock and pressure loss were still too big. To address these faults, an arc-junction was designed. Based on the flow fields of arc-junction, the eddy in the junction corner disappeared and the maximum of velocity peak declined compared to T-and Y-junction. Additionally, 8 series of arc-junction with different radiuses were tested to get the variation rule of velocity peak. Through the computation of the pressure loss of three junctions, the arc-junction had a lowest loss value, and its pressure loss reached the minimum value when the curvature radius is 35.42 mm, meanwhile, the velocity shock has decreased in a low phase.     

输流管的参数共振及共振响应的数值模拟与分析

研究了两端铰支输流管道在脉动内流作用下的参数共振问题。用数值方法分析了各种参数共振的响应曲线，其存在区域以及响应频率与脉动流频率之间的关系。研究结果发现，组合共振区域内发生两种不同的拟周期运动和组合周期运动。而且第一振型次谐波共振曲线延伸到组合共振区域。因此，在同一脉动频率下存在可发生多种不同运动的参数区域。     

点火发动机形成的受限喷流流场数值模拟

从曲线坐标下的气体Ｎ－Ｓ方程出发，采用ＥＮＯ差分格式，对点火发动机工作初期，在固体火箭发动机内腔形成的受限冷喷流流场进行数值模拟，在此基础上，分析了喷流的流场结构及特性。     

Boundary-layer transition prediction using a simplified correlation-based model

This paper describes a simplified transition model based on the recently developed correlation-based c ? Reht transition model. The transport equation of transition momentum thick-ness Reynolds number is eliminated for simplicity, and new transition length function and critical Reynolds number correlation are proposed. The new model is implemented into an in-house com-putational fluid dynamics (CFD) code and validated for low and high-speed flow cases, including the zero pressure flat plate, airfoils, hypersonic flat plate and double wedge. Comparisons between the simulation results and experimental data show that the boundary-layer transition phenomena can be reasonably illustrated by the new model, which gives rise to significant improvements over the fully laminar and fully turbulent results. Moreover, the new model has comparable features of accuracy and applicability when compared with the original c ? Reht model. In the meantime, the newly proposed model takes only one transport equation of intermittency factor and requires fewer correlations, which simplifies the original model greatly. Further studies, especially on separation-induced transition flows, are required for the improvement of the new model.     

Aerodynamic shape optimization for alleviating dynamic stall characteristics of helicopter rotor airfoil

In order to alleviate the dynamic stall effects in helicopter rotor, the sequential quadratic programming(SQP) method is employed to optimize the characteristics of airfoil under dynamic stall conditions based on the SC1095 airfoil. The geometry of airfoil is parameterized by the class-shape-transformation(CST) method, and the C-topology body-fitted mesh is then automatically generated around the airfoil by solving the Poisson equations. Based on the grid generation technology, the unsteady Reynolds-averaged Navier-Stokes(RANS) equations are chosen as the governing equations for predicting airfoil flow field and the highly-efficient implicit scheme of lower–upper symmetric Gauss–Seidel(LU-SGS) is adopted for temporal discretization. To capture the dynamic stall phenomenon of the rotor more accurately, the Spalart–Allmaras turbulence model is employed to close the RANS equations. The optimized airfoil with a larger leading edge radius and camber is obtained. The leading edge vortex and trailing edge separation of the optimized airfoil under unsteady conditions are obviously weakened, and the dynamic stall characteristics of optimized airfoil at different Mach numbers, reduced frequencies and angles of attack are also obviously improved compared with the baseline SC1095 airfoil. It is demonstrated that the optimized method is effective and the optimized airfoil is suitable as the helicopter rotor airfoil.     

Experiment of gas plasma plume deflection by magnetic control

To investigate the deflection effect of gas plasma plume controlled by magnetic field, a novel experimental scheme was presented. The Cs2CO3 catalytic ionization seeds were injected into the combustion chamber to obtain gas plasma on a high temperature magneto hydrodynamic (MHD) experiment rig. The plasma jet was deflected under the action of an external magnetic field, resulting in a thrust-vector effect. Particle image velocimetry (PIV) collected two-dimensional images of jet flow field. Through image processing and velocity vector analysis, the jet deflection angle can be obtained quantitatively. At 1800-2500K, the jet deflection was verified experimentally under the condition of 0.45T magnetic field strength. The results indicate that the jet deflection angle increases gradually with the increase of gas temperature, and above 2200K, the jet deflection angle increase obviously. In the process of gas plasma jet, it is feasible to realize the jet deflection controlled by MHD by adding an external magnetic field.