Volume 31, Issue 1

In the present paper, experimental and numerical investigations have been carried out on the film cooling characteristics of cylindrical hole, laidback fan shaped hole and doublefan shaped holes in the presence of various mainstream pressure gradients. Three momentum ratios: 1, 2 and 4, were measured. The pressure gradients, especially the adverse pressure gradient, improve the jet coverage and the jet lateral spread for cylindrical hole film cooling and 45° inclined doublefan shaped hole film cooling, especially under large momentum ratios. However, the effect of pressure gradient on the film cooling effectiveness of 90° inclined doublefan shaped hole is different from that of 45° inclined doublefan shaped hole. The film cooling effectiveness under favorable pressure gradient is the highest for 90° inclined hole. The effect of pressure gradients on the film cooling effectiveness of laidback fan shaped hole and 20° inclined doublefan shaped hole is weak because of the jets' good attachment on the wall. For all the holes, the normalized heat transfer coefficient h/h 0 under favorable mainstream pressure gradient is the highest under all the momentum ratios. Relative to the h/h 0 of zero pressure gradient, the h/h 0 of adverse pressure gradient is lower or close in the upstream region, but higher in the downstream region.

An active elastic support/dry friction damper is designed and experimental investigations on its effectiveness of reducing rotor vibration are carried out while using switch control and P control schemes. It is proven that the damper is very effective to reduce rotor vibration, and there is no changed of the critical speed of rotor system comparing to the passive damper. Experimental shows that the damper is easy to be controlled, quick response from a stable state to another stable state without instability, and only little electric power is needed in the control procedure. Such an active elastic support/dry friction damper is promising in practical application.

Unsteady operation of valveless pulse detonation engine results in unsteady gas dynamics of air inflow. In this paper, a simplified model has been developed to evaluate actual performance of pulse detonation engine with consideration of intake condition. The volume of plenum chamber, inflow area of pulsed detonation chamber and the operation frequency are considered as influencing factors on pulsed detonation chamber thrust performance. The simulation results show bigger plenum chamber volume leads to less inflow perturbation of pulsed detonation chamber. If the gas state of inflow is not determined by unsteady character, the negative thrust of pulsed detonation chamber will decrease with the increase in frequency. But when unsteady character has an effect on inflow, the negative thrust of pulsed detonation chamber increases with the increase in frequency. The experimental results of pulse detonation engine on test bench confirmed the simulation results.

This paper presents an original method for calculation of geometric parameters of the pipe diffuser and the proposition of a method for determination of flow parameters at the outlet of the diffuser. Proposed methods may be applied for calculations at compressor conceptual design stage. Results of few experimental tests of the pipe diffuser are also presented.

Because of the high rotating speed, big air flow rate and high exhaust temperature of the areoengine, strong noise occurs in the engine test process. In this paper, the power spectrum analysis method of the areoengine test noise was discussed, and the noise measurement and analysis experiments of a turboprop engine test were carried out. The noise level, main noise resource and noise characteristics of this turboprop engine were analyzed and the noise control performance of the aeroengine test bench was evaluated. The experimental results indicated that the noise analysis method was feasible, whose analysis results were consistent with the theory, and could be used to diagnose the areoengine fault by the engine test noise analysis. Meanwhile the experimental results could provide the reference to the noise reduction design of the areoengine test bench.

Low-speed subsonic jets are commonly encountered in many flow systems such as in chimney exhausts, impinging jets, inlets in combustors of diesel engines and gas turbines. Large-eddy simulation of a Mach 0.1, three-dimensional plane (square) turbulent air jet was performed. The Reynolds number of the jet based on the jet width was 3 × 10 4 . The width of the jet was 0.013 m. The aim of the present work was to develop a three-dimensional compressible parallel LES finite-volume code and validate it against an experimental free jet test case. A robust novel numerical scheme based on the blending of Riemann invariants and the exact Godunov solver, capable of handling low Mach number flows without preconditioning, was used. The Smagorinsky sub-grid scale model was used to model the unresolved stresses. An investigation was carried out into the self similarity behavior of the jet and the two-point correlations and the dissipation was computed. It is observed that istropicity of turbulence only exists in the v and w components and self-similar behavior was observed approximately beyond 90 jet widths downstream.

The present numerical work studies the flow field in subsonic axial compressor stator passages for: (a) preceding rotor sweep (b) preceding rotor re-staggering (three stagger angle changes: 0°, +3° and +5°); and (c) stator sweeping (two 20° forward sweep schemes). The following are the motives for the study: at the off-design conditions, compressor rotors are re-staggered to alleviate the stage mismatching by adjusting the rows to the operating flow incidence. Fundamental to this is the understanding of the effects of rotor re-staggering on the downstream component. Secondly, sweeping the rotor stages alters the axial distance between the successive rotor-stator stages and necessitates that the stator vanes must also be swept. To the best of the author's knowledge, stator sweeping to suit such scenarios has not been reported. The computational model for the study utilizes well resolved hexahedral grids. A commercial CFD package ANSYS® CFX 11.0 was used with standard k-w turbulence model for the simulations. CFD results were well validated with experiments. The following observations were made: (1) When the rotor passage is closed by re-staggering, with the same mass flow rate and the same stator passage area, stators were subjected to negative incidences. (2) Effect of stator sweeping on the upstream rotor flow field is insignificant. Comparison of total pressure rise carried by the downstream stators suggests that an appropriate redesign of stator is essential to match with the swept rotors. (3) While sweeping the stator is not recommended, axial sweeping is preferable over true sweeping when it is necessary.

The engine performance condition monitoring systems using various methods such as traditional methods including FSA, MCD, SOAP, etc., model based methods including GPAs, Observers, Party Equations and Parameter Estimations and soft computing methods including Neural Networks, Fuzzy Logic and Expert Systems have been developed to monitor the engine condition. This work proposes a practical condition monitoring system of a small turbojet engine to check not only the engine performance condition through comparing between the on-line performance measuring data and the clean performance data calculated by the base engine performance program but also the gas path component condition through comparing the component performance characteristics between the running degraded engine component and the clean engine component. Here the base performance simulation model is built using the inversely generated component maps from the measured performance data using the modified scaling method. The performance analysis results are compared with the experimental test data at the same operating condition. The proposed condition monitoring system is coded in a friendly GUI type program for easy practical application using commercial programs of MATLAB/SIMULINK and LabVIEW.

This paper presents the influence of rib height on heat transfer and friction factor augmentation in convergent rectangular channel with bottom rib-roughened walls has been conducted in experimentally. In this experiment the square sized ribbs at three different height were (3, 6 and 9 mm) used. A specified constant heat-flux is applied to the bottom surface of the test section and the ribs are arranged in the form of a staggered array. Measurements were taken of a convergent rectangular channel with an inlet aspect ratio of 1.25 and an exit aspect ratio of 1.35. This yields a rib height ( e ) to mean hydraulic diameter of the duct ( D m ) ratio of 0.0348, 0.0697 and 0.1046 respectively, with a fixed rib pitch ( p ) to test the section inlet height ( h in ) ratio of 0.6 along the sloped surface of the test section. The Reynolds number based on the mean hydraulic diameter ( D m ) of the channel was kept in a range of 20,000 to 60,000. The results from the ribbed channel are compared with that of the smooth convergent rectangular channel, to estimate the heat transfer enhancements from the ribbed channel. The comparison shows that among the tested convergent smooth channel, 3, 6 and 9 mm ribbed channel; the heat transfer from the channel with 6 mm rib height is better and showed comparatively lower friction loss than the other ribbed channels.