Laser-Doppler measurements of the turbulent mixing of two rectangular water jets impinging on a stationary pool

Abstract

Turbulent mixing of parallel jet flows has broad engineering applications. For example, in Gen IV conceptual nuclear reactors, high-temperature flows mix in the lower plenum before entering the secondary cooling system. The mixing condition needs to be accurately estimated and fully understood. In addition, massive computational works involved in the design process necessitate high-fidelity experimental data sets for benchmarking simulation results. The purpose of this study is to use laser Doppler anemometry, a non-intrusive measuring technique, to evaluate the mixing characteristics of two submerged parallel jets issuing from two rectangular channels. The jets with a small spacing ratio of 3.1 were at room temperature. Flow characteristics including distributions of mean velocities, turbulence intensities, and Reynolds stresses were studied for the cases with equal and non-equal discharge velocities. The merging point (MP) was found to be between y/a = 1.72 and y/a = 3.45. The combining point (CP) was at y/a = 15.52. The Reynolds shear stress, a measure of the intensity of momentum transfer, reached its maximum after the merging point. An uncertainty analysis indicated that the average standard deviations of the streamwise mean velocity U and turbulence intensity Urms at all locations in the five days' measurements were 1.5% and 1.6%, respectively. Spectral analyses including fast Fourier transform, power spectral density estimation and continuous wavelet transform revealed the scale and the evolution in time of varied-size eddies in the mixing region of the flow. Repeating flow structures were observed in different time segments. The experimental data obtained from the LDA measurements of the averaged quantities and transient are not only valid for benchmarking steady-state numerical simulations using turbulence models to solve RANS equations but they also enlarge the database of the experimental data for twin jets.

Simulations of Twin Turbulent Planar-Like Jets Injected Into a Large Volume Using RANS

“…Based on this information, the Reynolds number of 9100 is defined based off the . This is consistent with the Reynolds number definition used by the experimental works [3,4,6]. The twin jets are separated (based on the centerline of each jet) with a spacing of 17.8 mm which results in a spacing ratio (S/a) of $3.07.…”

“…2 was made to be almost entirely transparent for additional experiments using noninvasive measurement techniques, such as laser Doppler velocimetry (LDV), particle image velocity (PIV), and laser-induced fluorescence. The TJWF was moved to Texas A&M University, where LDV and PIV data have been collected for CFD validation efforts [4][5][6][7] using the same boundary conditions as Crosskey and Ruggles. The LDV results of Wang et al includes streamwise velocity and vorticity profiles, Reynolds stress profiles, and merge/combined points.…”

“…1). This includes comparisons to historical insights found in literature and recent experimental efforts at the University of Tennessee, Knoxville [3], and Texas A&M University (TAMU) [4][5][6][7]. Utilizing experimental data collected in the twin jet water facility (TJWF), the STAR-CCMþ code was benchmarked using the steady Reynoldsaveraged Navier-Stokes (RANS) framework.…”

Numerical Study and Correlations Development on Twin-Parallel Jets Flow With Non-Equal Outlet Velocities

“…The nozzles exit Reynolds number was approximately 9100 and the turbulent intensity was 8%. Wang et al (2016) found that the longitudinal location of the merge point was between X = 1.72 and X = 3.45 and that of the combined point was X = 15.52. The turbulence study showed that the outer boundary of the combined jet and the outer edges of the two jets had higher turbulence levels due to high velocity gradients in those regions.…”

“…They found that the merge point location depends not only on the nozzles spacing but also on the nozzles exit condition such as the turbulent intensity. Recently, Wang et al (2016) experimentally studied two water jets flow issue from two parallel rectangular channels using two-component LDA technique. The nozzle spacing and the aspect ratio were respectively 3.1 and 15.…”