An Experimental Investigation of Two-Point Correlations in Two- and Three-Dimensional Turbulent Boundary Layers |
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Authors: | M Semih Ölçmen Roger L Simpson Michael Goody |
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Institution: | (1) Department of Aerospace and Ocean Engineering, Virginia Polytechnic Institute and State University, Blacksburg, VA, 24061, U.S.A |
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Abstract: | Two-point correlation measurements of the wall normal fluctuating velocities were made in two-dimensional (2-D) and pressure-driven
three-dimensional (3-D) turbulent boundary layers. These data are needed for characterization and modeling of active-motion
length scales, especially for 3-D flows. The fine-probe-volume data were measured using two custom-designed laser-Doppler-velocimeter
fiber-optic probes. The data are relatively free of noise, signal broadening, and bias effects.
Favorable comparisons with direct-numerical-simulation (DNS) results in the near-wall region of the 2-D flow validate the
experimental techniques used here. For a given fixed probe location, non-dimensional correlation values scale best on the
probe separation. For both the 2-D and 3-D cases, peak correlations lie along a line inclined away from the wall at 11° and
8°, respectively, which suggests the existence of an outgoing characteristic line affected by only the upstream flow. The
decay of the correlation coefficient occurs nearer the wall than away from the wall relative to the fixed probe location.
The variations for the 3-D flow correlations are similar to the 2-D variations, but with longer Δ x
+and Δ y
+ decay distances, probably because of the 3-D flowacceleration. While the spanwise variation of the correlationcoefficients
is symmetric about the fixed point for the 2-D case asdictated by reciprocity, the 3-D case shows a large asymmetry for spanwise
variations Δ z
+ < 68. The profiles at higher Δ z
+ are more symmetric. In general, at a given y the maximum correlation is skewed toa non-zero Δ z. It appears that the skewing of the correlation coefficient in the z direction tracks the sign of
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This revised version was published online in July 2006 with corrections to the Cover Date. |
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Keywords: | turbulence structure three-dimensional turbulent boundary layers |
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