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Research of Vortex Identification Algorithm and Its
Application to Aircraft Wake Flow Vortices
R Zhu
1
, Z Y Chen
1
, S Li
1
, Y Q Tan
1
, Y R Mo
1
, F Bao
1
and Z R Liu
*
Department of Power Engineering, School of Aerospace Engineering, Xiamen
University, Xiamen 361005, China
Corresponding author and e-mail: Z R Liu, lzr1222@126.com
Abstract. Vortex identification is very critical for PIV (Particle Image Velocimetry) post-
processing to obtain the precise vortex formation. The research focuses on studying &
comparing several popular vortex identification methods which are based on velocity gradient
tensor derived the second invariant Q , the characteristic equation discriminant
, the
complex eigenvalue imaginary part
ci
and the pressure second eigenvalue
2
. By comparing
and analyzing different vortex identification algorithms to detect the vortex region, the
criteria with the best display effect is applied to the aircraft vortex data of the four vortices
system to study the influence of the initial vortex and the initial position of the vortex on the
dissipation of the main vortex. The research results indicate that the higher small-vortex
initial circulation will speed up primary vortex dissipation and the wake vortex strength may
reach weakest as the small-vortex initial circulation is of an appropriate value. The closer the
initial position of small-vortex to primary vortex will also speed up vortices interactions but
non-linearly related to primary vortex dissipation, and if the distance is too close, it will cause
the small vortex to be thrown off by the main vortex.
1. Introduction
The research on vortex is always frontier
multidimensional & nonlinear complicated mechanism and its importance to engineering applications
[1]. The PIV testing technology is essentially an image analysis technology. The speed field obtained
by the PIV is only an intermediate product for studying the complex flow and needs further post-
processing to extract important flow field information. In fact, some recent vortex identification
criteria based on wavelet analysis have been proved to be very effective [2, 3]. The vortex
identification algorithm for 2D PIV velocity field is deduced and programmed in Matlab in this paper.
The vortex identification method for 3D velocity field is also deduced and programmed in Tecplot to
be compared with 3D numerical experiments results. Applying optimal method to aircraft wake flow
optimizes flow formations.
In the actual PIV measurement process, due to improper exposure of the collection device, uneven
concentration of tracer particles, noise interference, etc., the peak value of the correlation function in
the analysis process is likely to be indeterminate, resulting in spurious vectors in the velocity field.
Zhu, R., Chen, Z., Li, S., Tan, Y., Mo, Y., Bao, F. and Liu, Z.
Research of Vortex Identification Algorithm and Its Application to Aircraft Wake Flow Vortices.
In Proceedings of the International Workshop on Materials, Chemistry and Engineering (IWMCE 2018), pages 143-151
ISBN: 978-989-758-346-9
Copyright © 2018 by SCITEPRESS – Science and Technology Publications, Lda. All rights reserved
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