An Experimental Study on Transonic Convex-Corner Flows

Abstract

Improving aircraft performance is one of the major goals in the aviation design In the past decade there have been many attempts to improve the aerodynamic efficiency of aircraft One of the methods is to maximize lift-to-drag ratio in different flight conditions To achieve this the wing of airplane must be able to change its configuration using deflected control surface Such device like flaps and ailerons could be employed to provide variable camber control within the operational flight envelopes Previous investigations have shown that the convex corner is an idealized configuration that be used to model the compressible flows over the deflection control surface at off-design condition The general characteristics of the flowfield include sudden expansion near the corner followed by recompression In the research presented in this dissertation a series of experiments of transonic convex corner flows were performed to investigate the aerodynamic characteristics and to gain a good insight into the interaction of a shock wave and a turbulent boundary layer First two flat plates with different lengths were used to develop naturally different incoming boundary layer thicknesses or Reynolds numbers The Reynolds number ranged from 8 04 × 104 to 1 63 × 105 Compared to subsonic expansion flow the Reynolds number has an influence on the flow expansion and compression near the corner apex in the transonic flow regime The subsequent work focused on transonic round convex-corner Test models with three different radii of curvature from 13 7 to 41 7 times the upstream boundary layer thickness were employed The total turning angles were 13- 15- and 17-deg It was found that the peak Mach number decreased with increasing radius of curvatures for a given turning angle Finally experiments were performed wherein a presence of bi-convex corner The total turning angle ? ranged from 10- to 17-deg in which the first convex-corner angle ?1 was 5- or 7-deg It was known that the length of the first corner L1 also plays an important role With increasing L1 the less flow expansion is observed while a shorter L1 resulted in a more significant decrease in the amplitude of (σp/pw)max Not only the bi-convex corner but also the round convex-corner was observed dual expansion process in transonic expansion flows In addition a delay in the transition from subsonic to transonic flows was found in both test configurations A similarity parameter β (=M^2 η/√(1-M^2 )) was also employed to correlate the Mpeak (σp/pw)max and shock-induced boundary-layer separated length The experimental results showed that the shock structure boundary-layer separation and peak fluctuating pressure were dependent on freestream Mach number turning angle and model geometry The two-threshold method was also used to estimate the zero-cross frequency The relationship between peak pressure fluctuations and zero-cross frequency was obtain and compared with results from the studies using sharp convex corner

Date of Award	2014 Nov 7
Original language	English
Supervisor	Keh-Chin Chang (Supervisor)