OJFDOpen Journal of Fluid Dynamics2165-3852Scientific Research Publishing10.4236/ojfd.2012.24A019OJFD-25788ArticlesPhysics&Mathematics Effects of Supersonic Nozzle Geometry on Characteristics of Shock Wave Structure higeruMatsuo1*KousukeKanesaki2JunjiNagao2Md.Tawhidul Islam Khan1ToshiakiSetoguchi3HeuyDong Kim4Graduate School of Science & Engineering, Saga University, Saga, JapanInstitute of Ocean Energy, Saga University, Saga, JapanDepartment of Advanced Technology Fusion, Saga University, Saga JapanSchool of Mechanical Engineering, Andong National University, Andong, Korea* E-mail:matsuo@me.saga-u.ac.jp(HM);261220120204181186September 1, 2012October 3, 2012 October 16, 2012© Copyright 2014 by authors and Scientific Research Publishing Inc. 2014This work is licensed under the Creative Commons Attribution International License (CC BY). http://creativecommons.org/licenses/by/4.0/

Interaction between the normal shock wave and the turbulent boundary layer in a supersonic nozzle becomes complex with an increase of a Mach number just before the shock wave. When the shock wave is strong enough to separate the boundary layer, the shock wave is bifurcated, and the 2nd and 3rd shock waves are formed downstream of the shock wave. The effect of a series of shock waves thus formed, called shock train, is considered to be similar to the effect of one normal shock wave, and the shock train is called pseudo-shock wave. There are many researches on the configuration of the shock wave. However, so far, very few researches have been done on the asymmetric characteristics of the leading shock wave in supersonic nozzles. In the present study, the effect of nozzle geometry on asymmetric shock wave in supersonic nozzles has been investigated experimentally.

Compressible Flow; Asymmetric Shock Wave; Supersonic Nozzle; Experiment1. Introduction

The supersonic flow fields with the pseudo-shock wave are observed in some apparatuses, such as the separation part of a SCRAM jet engine, a high pressure gas piping system, supersonic diffuser and so on.

In the supersonic internal flow, interaction between the shock wave and the boundary layer is very complex and induces the separation of boundary layer. When the shock wave is strong enough to separate the boundary layer, the shock wave is bifurcated and more shock waves are formed downstream of the leading shock wave. The series of shock waves are called shock train. This shock train and the resulting mixing region construct a pseudo-shock wave [1], which plays a role similar to that of a single normal shock wave. The leading shock wave of the pseudo-shock wave is classified into λ-type and X-type shock waves by Mach number or Reynolds number.

Neumann and Lustwerk [2] indicated that static pressure on the wall increased monotonously, and the length of the pseudo-shock wave, defined as the distance from the starting point of the pressure rise to point of the maximum pressure, was 8 - 13 times the duct diameter.

Tamaki et al. [3,4] reported that with an increase of the main flow Mach number, the configuration of the pseudo-shock wave changed from λ-type shock wave to X-type shock wave and the range of the shock wave was expanded. However, the asymmetric characteristics of the leading shock wave have not been investigated satisfactorily.

Numerical and experimental researches on the symmetric and asymmetric shock wave system in a planar nozzle were presented by Xiao et al. [5] and Papamoschou et al. [6-8]. Papamoschou et al. [6,7] revealed that either of two distinct systems is occurred depending on area ratio (cross-sectional area at the nozzle exit to crosssectional area at the nozzle throat). One is the symmetrical λ-type shock wave system and the other is the asymmetrical separation with lager λ-type foot. Thus, some researches have been done on the effect of the area ratio on asymmetric characteristics of the leading shock wave in supersonic nozzles. However, there are few researches for the effects of nozzle length and nozzle throat on the characteristics.

The purpose of this study is to investigate the effects of the nozzle length with parallel part and the position of nozzle throat on the characteristics of asymmetric shock wave in supersonic nozzles experimentally.

2. Experimental Apparatus and Method2.1. Experimental Apparatus

Figure 1 shows a schematic diagram of the experimental apparatus. The apparatus is consisted of compressor, air drier, air reservoir, electronic control valve, plenum chamber and nozzle. Plenum chamber is placed upstream of the supersonic nozzle. Compressed dry air was used as a working gas. Optical glass windows are installed on both the side walls of the test section for flow visualization.

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