URANS of turbulent flow and heat transfer in divergent swirl tubes using the k-ω SST turbulence model with curvature correction

Abstract

In the current work, the turbulent flow and heat transfer in divergent swirl cooling tubes is studied numerically by using the open source CFD code OpenFOAM. The k-ω SST turbulence model with curvature correction, i.e., the k-ω SSTCC model, is used to compute the strong turbulent swirling flow. The unsteady solver “rhoPimpleFoam” is adopted in the computation and a time-averaging operation is implemented for the pressure, velocity and temperature fields to cover the effect of large-scale, low-frequency deterministic fluctuations of the vortex breakdown phenomenon. To generate high-quality grids, different parts of the swirl tubes are meshed with different block structures in ICEM and the Arbitrarily Coupled Mesh Interface (ACMI) boundary condition is used to couple the neighboring segments with non-conformal grids. The current model is validated by comparing the numerical results of a swirl tube with constant diameter to experimental data and numerical results from literature. In this study we investigated the turbulent heat transfer enhancement in a divergent swirl tube that features two 180°-displaced tangential inlets and a divergence angle of 0.596°. Moreover, the influence of axially multiple tangential inlets is studied for the same divergence angle. The current work demonstrates that the computationally cheap k-ω SSTCC model can predict the flow and heat transfer performances in a swirl tube with reasonable accuracy. Additionally, it is found that the Nu number of the divergent swirl tube with 180°-displaced inlets (S2D), is about 3.57 times higher than the one in a smooth tube with axial flow, and it is slightly lower (by 13%) than that of constant-diameter swirl tube (S2C), while its decrement of pressure drop is notable (by40%) compared with S2C. Axially-displaced multiple inlets can result in a tremendous reduction of pressure drop for swirl tubes by over 90% at the cost of a limited decrease in the Nu number (by ˜10%) compared to the swirl tube S2D.