Background-Oriented Schlieren (BOS) for Scramjet Inlet-isolator Investigation

Azam Che Idris,Kin Hing Lo,Konstantinos Kontis,Mohd Rashdan Saad

doi:10.1088/1757-899x/370/1/012003

Abstract

Background-oriented Schlieren (BOS) technique is a recently invented non-intrusive flow diagnostic method which has yet to be fully explored in its capabilities. In this paper, BOS technique has been applied for investigating the general flow field characteristics inside a generic scramjet inlet-isolator with Mach 5 flow. The difficulty in finding the delicate balance between measurement sensitivity and measurement area image focusing has been demonstrated. The differences between direct cross-correlation (DCC) and Fast Fourier Transform (FFT) raw data processing algorithm have also been demonstrated. As an exploratory study of BOS capability, this paper found that BOS is simple yet robust enough to be used to visualize complex flow in a scramjet inlet in hypersonic flow. However, in this case its quantitative data can be strongly affected by 3-dimensionality thus obscuring the density value with significant errors.

Highlights

The Background-Oriented Schlieren (BOS) technique, which has been gaining its popularity today, is suitable for calculating the density increase across an oblique shock
The method was first presented by Dalziel et al in late 1990s as the “synthetic schlieren” [5 – 7]. They demonstrated that the displacements of light-ray path from random dots set up on the background of a changing density volume can be processed by using cross-correlation software “borrowed” from Particle Image Velocimetry (PIV) methods
The model movement was corrected using ‘cp2tform’ function in MATLAB 7.10.0 (R2010a), where control points were selected on both figures and the algorithm automatically applied rotation and translation on figure 5(b), so that the control points on both figures agree with each other

Summary

Introduction

The Background-Oriented Schlieren (BOS) technique, which has been gaining its popularity today, is suitable for calculating the density increase across an oblique shock. The calculated density gradient can be used to estimate the overall performance of a scramjet inlet using the concept shown by Idris et al [1]. Compared to their method where average isolator flow properties were inferred from the pressure map on sidewall, two-dimensional BOS technique would result in spanwise-integrated density field for the whole isolator [2]. To cite this article: Azam Che Idris et al 2018 IOP Conf. - Measurement of spray characteristics using the background-oriented schlieren technique Junyong Lee, Namho Kim and Kyoungdoug Min This content was downloaded from IP address 130.209.115.106 on 18/06/2018 at 11:54. Azam Che Idris 1,*, Mohd Rashdan Saad, Kin Hing Lo2 and Konstantinos Kontis Abstract

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Results

Conclusion