Author: Chen, Siyu
Title: The calibration of high-speed ludwieg tube wind tunnel and experimental investigation of high-speed boundary layer transition on a flat plate
Advisors: Wen, Chih-yung (AAE)
Degree: M.Sc.
Year: 2021
Subject: Fluid mechanics
Wind tunnels
Boundary layer
Hong Kong Polytechnic University -- Dissertations
Department: Department of Mechanical Engineering
Pages: x, 92 pages : color illustrations
Language: English
Abstract: In this paper, the high-speed Ludwieg wind tunnel in the Hong Kong Polytechnic University was commissioned and calibrated. Some qualitative and quantitative test techniques are developed that can be applied to high-speed flows. Based on this wind tunnel and testing methods, the flat plate boundary layer transition study was conducted. In this paper, firstly, commission and improve the wind tunnel experimental platform. It is found that the burst pressure of the aluminum alloy diaphragm is proportional to the thickness of the diaphragm. Thus, using different thicknesses of metal diaphragms can achieve different unit Reynolds number experimental conditions. By applying fiberglass tape to the diaphragm, the burst pressure can be kept consistent, and the diaphragm fragments can be prevented from falling off. The optical path of the Schlieren system is improved to achieve a higher spatial resolution of the camera, which can capture the detailed structure of the boundary layer. Using the non-crystal magnetic ring dampened the electrical noise of the system, the signal-to-noise ratio of the data acquisition system was improved. Secondly, calibration of the wind tunnel flow field was carried out. The wind tunnel was dynamically and statically calibrated by using the Pitot-pressure rake. The Pitot tube and Schlieren results show that the wind tunnel's effective test time is about 24 ms. The flow field has satisfactory uniformity in the horizontal and vertical range of 200 mm. The Mach number of the free stream is calculated using the isentropic flow relation equation to be about 4.12, which does not change significantly with the unit Reynolds number. The incoming flow fluctuation is less than 2%, mainly low-frequency noise. Finally, the study of the flat plate boundary layer transitions is investigated. Linear stability theory shows that as the unit Reynolds number increases, the frequency of the instability wave increases, and the amplification of the instability wave becomes more significant at the exact location. Schlieren measurement of the boundary layer thickness was used to find the transition onset. As the unit Reynolds number increased, the transition point became more forward, and the Reynolds number increased. The power spectrum density(PSD) analysis of the pressure data of the flat plate obtained the pressure spectral characteristics of different locations at different unit Reynolds numbers.
Rights: All rights reserved
Access: restricted access

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