On the development of coherent structure in a plane jet (Part 3, multi-point simultaneous measurement of main streamwise velocity and the reconstruction of velocity field by the KL expansion)

• Published in: JSME international journal. Series B, Fluids and thermal engineering Vol. 49; no. 3; pp. 722 - 730
• Main Authors: SAKAI, Yasuhiko, TANAKA, Nobuhiko, YAMAMOTO, Mutsumi, KUSHIDA, Takehiro
• Format: Journal Article
• Language: English
• Published: Tokyo Japan Society of Mechanical Engineers 01.08.2006
• Subjects: Exact sciences and technology; Fluid dynamics; Fundamental areas of phenomenology (including applications); Instrumentation for fluid dynamics; Jets; Physics; Turbulent flows, convection, and heat transfer; Flapping Phenomenon; Turbulence; Turbulent flow; Coherent Structure; Flow Measurements; Spatial correlation; Instrumentation; Experimental study; Plane geometry; Eigenvalues; Jet; Spatial Velocity Correlation; Jets; Karhunen-Loeve transforms; Velocity measurement; Vortex; Hot wire anemometers; Turbulence structure; Karhunen Loève Expansion
• ISSN: 1340-8054
• DOI: 10.1299/jsmeb.49.722

In order to clarify the dynamics of the coherent structure in a turbulent plane jet, the simultaneous measurement of the main streamwise velocity at 21 points in the self-preserving region of a turbulent plane jet has been performed by an array of I-type hot-wire probes. Then the KL (Karhunen-Loeve) expansion was applied to extract the coherent structure in the jet. The total number of eigenfunctions (modes) is N = 21, which corresponds to the number of probes. The eigenfunctions (modes) are numbered in order of magnitude of their corresponding eigenvalues. From the investigation of the random coefficients and the eigenfunctions (modes), it is found that the low-numbered (energetic) modes represent the large scale (coherent) structure, the middle-numbered modes represent the finer (small-scale) random structure, and the higher-numbered modes contribute mainly to the intermittent structure in the outer edge region. From the spatio-temporal velocity field reconstructed by the first KL mode, it is found that there exist a pair of fluid lumps with the positive and negative stream-wise velocity fluctuation on the opposite sides of the jet centerline, and the signs of velocity fluctuation for those fluid lumps change alternately as time proceeds. These characteristics are consistent with the so called 'jet flapping' phenomenon.