On the numerical modelling of impinging jets heat transfer

Licentiatavhandling, 2011

This thesis collects two studies on heat transfer in impinging jets and on methods for modeling flows of this kind using CFD. Stationary impinging jets with different nozzle to wall distances (z/D = 2 and 6) and Re (10000, 20000, 23000, 30000) are modeled. Steady-state models capture the important features of heat transfer in these jets. The inlet velocity profile plays an important role on the results. The k-ε and k-ω turbulence models do not offer adequate performance. However, the V2F model generates useful results even with low order discretization schemes. The effects of varying the mesh density and topology also studied, and the computational cost of different model set-ups is compared. Transient simulations were shown to be useful for studying the dynamics of turbulent flow in the impinging jet shear layer. Simulations are performed using the LES model, which resolves the turbulent fluctuations, and with the DES, V2F, and k-ε turbulence models, which do not; a number of parameters are varied during the testing of the LES model. The effects of inlet turbulence were studied by superimposing synthetic turbulent fluctuations at the inlet. The LES, DES and V2F models are shown to capture the time-average heat transfer coefficient in a fashion that agreed well with the available experimental data.