Heat transfer benchmarks for laminar and turbulent impinging jets

Courtesy of FSC Applied Chemistry

A schematic of the problem is shown in Fig.1. A planar jet is impinging against a plate of length 2L and kept at the constant temperature Tw. The jet is emitted from rectangular nozzle with the width 2d = 1.29e-3 m and length l=7.62e-2 m. The nozzle's outlet is located h = 6.35e-3 m above the plate. At the inlet of the nozzle, a uniform velocity profile, U0 and constant temperature, T0, are specified. Considering the symmetry of the problem the computational domain shown in Fig.1 includes only a half of the physical domain. The flow was computed using Coolit CFD software, which solves the Navier-Stokes or the Reynolds averaged Navier-Stokes equations depending on whether laminar or turbulent flow was considered. For turbulent jets, we used the eddy viscosity turbulence model without wall functions [1] offered by Coolit. The computed results were compared with impinging jets experiment by Gardon and Akfirat [2].

A comparison of computed and experimentally measured heat flux along the plate at two values of Reynolds numbers was carried out. The Reynolds number was based on the velocity at the nozzle inlet and nozzle width, Re= U02d/n, is presented in Fig.2. In the laminar flow regime, Re=450, the agreement of the predicted and measured heat flux values is virtually ideal. For the turbulent flow, Re=2750, there is a local discrepancy in the vicinity of the region where the transition to turbulence most likely occured. The exact transition point cannot be predicted by any of the existing turbulence models and such behavior is expected. The key parameters in practical simulations, however, is not the point distribution of the heat flux but the integral heat flux, for which the model provided an excellent agreement.

References:

[1] M. Strelets, M. Shur, L. Zaikov, A. Gulyaev, V. Kozlov, and A. Secundov, "Comparative Numerical Testing of One- and Tow-Equation Turbulence Models for Flow with Separation and reattachment", AIAA Paper, 95-0863.

[2] R Gardon, J. C. Akfirat, "Heat Transfer Characteristics of Impinging Two-Dimensional Air Jets," Journal of Heat Transfer, ASME, Series C, vol. 86, pp. 101-108, 1966.

Figure 1. Schematic of the experiment.
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Figure 2. Comparison of Coolit predictions with experiment for heat flux distribution along plate surface for turbulent jets.
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Figure 3. Comparison of Coolit predictions with experiment for heat flux distribution along plate surface for turbulent jets.
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Figure 4. Flow animation for pulsating jets.
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