EXPERIMENTAL AND NUMERICAL INVESTIGATION OF FLOW ...

Journal of Russian Laser Research, Volume 29, Number 4, 2008

EXPERIMENTAL AND NUMERICAL INVESTIGATION OF FLOW SEPARATION IN A SUPERSONIC NOZZLE

Slavica Risti´ c1 , Mirko Kozi´ c2 , and Mirjana Puhari´ c1

1 Institut

Go˘ sa Milana Raki´ca 35, Beograd 11000, Serbia 2 VTI (Military Technical Institute) Ratka Risanovi´ca 1, Beograd 11111, Serbia e-mail: s1avce @ yahoo.com Abstract The flow in a two-dimensional symmetric convergent–divergent supersonic nozzle with and without a deflector at the exit plane was tested experimentally and numerically. Combined optoelectronic devices were used to demonstrate the possibilities of the shadow and schlieren methods and holographic interferometry for the flow visualization especially in the separation region. A series of experiments was performed in a trisonic wind tunnel (VTI, Beograd). The experimental results obtained using optical methods are compared with the pressure measurements and numerical calculations. Numerical results were obtained using a code for solving the average Navier–Stokes equations. Five structured meshes with different resolutions and two turbulent models were employed. The coupled influence of the mesh resolution and the order of accuracy of the used numerical scheme is analyzed.

Keywords: supersonic nozzle, optical methods, flow separation, flow visualization, CFD, pressure measurements.

1.

Introduction

Flow separation caused by a deflector placed at the exit plane of a two-dimensional symmetric convergent–divergent supersonic nozzle is examined experimentally and numerically for comparing the experimental and numerical flow-visualization effects and the pressure distribution. Flow visualization is an important tool in experimental fluid mechanics [1]. Optical methods enable visualization and determination of aerodynamical-flow field variables in the total volume of a test section (density, pressure, flow velocity, Mach number, location of shock and expansion waves, nature and transformation of boundary layer, etc.) [1–6]. There are three principal optical methods of flow visualization, namely, the shadow method, the schlieren method, and interferometry. The shadowgraph methods are sensitive to changes of the second derivative of density and can be used for fine visualization of turbulent compressible flows. The schlieren technique is a well-known method of visualization of the density gradients in compressible flows [1, 4, 6]. It is most commonly used as a qualitative method. Holographic interferometry is an optical method that enables complete two-dimensional flow testing using only one hologram. The flow is not disturbed by using this method. The flow density can be measured directly using interferometry. The greatest advantage of the holographic interferometer in Manuscript submitted by the authors in English on June 27, 2008. c 1071-2836/08/2904-0377 2008 Springer Science+Business Media, Inc.

377