小型涡轮平面叶栅试验段设计

Performance improvement of the high-load transonic turbine is the key method of improving the thrustto-weight ratio or the power density of gas turbine engines. In order to investigate the flow behaviors inside the high load turbine cascades, a linear turbine cascade test section is designed, which enables the Schlieren photography and static pressure measurement along the cascade profile can be conducted. Variable pitch is realized in the test section to achieve different Zweifel coefficients. Due to the capability limitation of the air supplier, the test section is designed to have only5 blade channels with shortened blade height to achieve high Mach number flow conditions. Numerical investigations were carried out to investigate the wall effect and its in fluences on the flow fields inside the test section. The result indicates that the shape of the connecting part of the test section has a significant influence on the flow similarity among different blade passages. With the proper design, a good repetition flow is achieved between neighbored blade passages.

Parameter study on numerical simulation of corner separation in LMFA-NACA65 linear compressor cascade

Large-eddy simulation（LES） is compared with experiment and Reynolds-averaged Navier-Stokes（RANS）, and LES is shown to be superior to RANS in reproducing corner separation in the LMFA-NACA65 linear compressor cascade, in terms of surface limiting streamlines,blade pressure coefficient, total pressure losses and blade suction side boundary layer profiles. However, LES is too expensive to conduct an influencing parameter study of the corner separation.RANS approach, despite over-predicting the corner separation, gives reasonable descriptions of the corner separated flow, and is thus selected to conduct a parametric study in this paper. Two kinds of influencing parameters on corner separation, numerical and physical parameters, are analyzed and discussed： second order spatial scheme is necessary for a RANS simulation; incidence angle and inflow boundary layer thickness are found to show the most significant influences on the corner separation among the parameters studied; unsteady RANS with the imposed inflow unsteadiness（inflow angle varying sinusoidally with fluctuating amplitude of 0.92°） does not show any non-linear effect on the corner separation.

Experimental Investigation of Effects of Reynolds Number and Incidence Angle on Secondary Flow within a Linear Blade Cascade

The kinetic energy loss and the secondary loss downstream of a high turning nozzle cascade were investigated.Influence of the incidence angle(i=-25°,0°and 25°)and Reynolds number(Re_(2,is)=0.8×10^(5),1.2×10^(5),2.5×10^(5) and 4.5×10^(5))were studied on two cascade configurations defined by different pitch to chord ratio(t/c=0.6 and 0.9),respectively.Measurements at the cascade inlet were performed by means of Preston tube,while at the cascade outlet by means of miniature pyramid five-hole pressure probe.An effect of studied parameters on the flow field at the cascade outlet was shown by the distribution of the kinetic energy loss,secondary loss,mix-out loss and streamwise vorticity.

Experimental Research of Surface Roughness Effects on Highly-Loaded Compressor Cascade Aerodynamics

Aircraft engines deteriorate during continuous operation under the action of external factors including fouling, corrosion, and abrasion. The increased surface roughness of compressor passage walls limits airflow and leads to flow loss. However, the partial increase of roughness may also restrain flow separation and reduce flow loss. It is necessary to explore methods that will lower compressor deterioration, thereby improving the overall performance. The experimental research on the effects of surface roughness on highly loaded compressor cascade aerodynamics has been conducted in a low-speed linear cascade wind tunnel. The different levels of roughness are arranged on the suction surface and pressure surface, respectively. Ink-trace flow visualization has been used to measure the flow field on the walls of cascades, and a five-hole probe has been traversed across one pitch at the outlet. By comparing the total pressure loss coefficient, the distributions of the secondary-flow speed vector, and flow fields of various cases, the effects of surface roughness on the aerodynamics of a highly loaded compressor cascade are analyzed and discussed. The results show that adding surface roughness on the suction surface and pressure surface make the loss decrease in most cases. Increasing the surface roughness on the suction surface causes reduced flow speed near the blade, which helps to decrease mixing loss at the cascades outlet. Meanwhile, adding surface roughness on the suction surface restrains flow separation, leading to less flow loss. Various levels of surface roughness mostly weaken the flow turning capacity to various degrees, except in specific cases.

Experimental and Numerical Investigation of the Unsteady Tip Leakage Flow in Axial Compressor Cascade

For convenience of both measurement and adjusting the clearance size and incidence, the current research is mainly conducted by experiments on an axial compressor linear cascade. The characteristics and the condition under which the unsteadiness of tip leakage flow would occur were investigated by dynamic measuring in different clearances, inlet velocities and incidences. From the experiment it is found that increasing tip clearance size or reducing rotor tip incidence can affect the strength of the tip clearance flow. Then the experimental results also indicate the tip leakage shows instability in certain conditions, and the frequency of unsteadiness is great influenced by inflow angle. The condition of occurrence of tip leakage flow unsteadiness is when the leakage flow is strong enough to reach the pressure side of the adjacent blade. The main cause of tip leakage flow unsteadiness is the tip blade loading.

Aerodynamic Comparison between Increasing Cascade Pitch and Turning Angle in the Highly-Loaded Design

Theoretical and numerical study was carried out based on a linear turbine cascade(the Basic cascade)to compare the influences of the increased cascade pitch and turning angle in this paper.On one hand,the two highly-loaded designs both reduced the stability of flow field through enhancing adverse pressure gradient and span-wise pressure gradient of the fluid near suction surface.Therefore,the two highly-loaded designs would both result in thicker boundary layer and stronger secondary flow,so the secondary loss would be increased and more difficult to suppress in the highly-loaded cascades.On the other hand,the two highly-loaded designs showed different influences on the pitch-wise migration of the fluid near the endwall(cross flow)because of the different load enhancing mechanisms.In other words,the increased cascade pitch(TCx highly-loaded design)would delay the pitch-wise migration of the horseshoe vortex because of the increased channel width,while the increased turning angle(Turn highly-loaded design)would do the opposite because of the increased pitch-wise pressure gradient.As a result,the enhancement of the interaction between the fluid near the suction surface and the cross flow would be much stronger in the Turn highly-loaded design than the TCx highly-loaded design,and the span-wise developing tendencies of vortexes and fluid near the suction surface would show much stronger enhancing tendency in the former than the latter.

Sliding mode tracking control for miniature unmanned helicopters

A sliding mode control design for a miniature unmanned helicopter is presented. The control objective is to let the helicopter track some predefined velocity and yaw trajectories. A new sliding mode control design method is developed based on a linearized dynamic model. In order to facilitate the control design, the helicopter＇s dynamic model is divided into two subsystems,such as the longitudinal-lateral and the heading-heave subsystem. The proposed controller employs sliding mode control technique to compensate for the immeasurable flapping angles＇ dynamic effects and external disturbances. The global asymptotic stability（GAS） of the closed-loop system is proved by the Lyapunov based stability analysis. Numerical simulations demonstrate that the proposed controller can achieve superior tracking performance compared with the proportionalintegral-derivative（PID） and linear-quadratic regulator（LQR） cascaded controller in the presence of wind gust disturbances.