Improved modeling of near-wall heat transport for cooling of electric and hybrid powertrain components by high Prandtl number flow

Paper #:
  • 2017-01-0621

Published:
  • 2017-03-28
Abstract:
RANS computations of heat transfer involving wall bounded flows at elevated Prandtl numbers typically suffer from a lack of accuracy and/or increased mesh dependency. This can be often attributed to an improper near-wall turbulence modeling and the deficiency of the wall heat transfer models (based on the so called P-functions) that do not properly account for the variation of the turbulent Prandtl number in the wall proximity (y+<5) [1]. As the conductive sub-layer gets significantly thinner than the viscous velocity sub-layer (for Pr >1), treatment of the thermal buffer layer gains importance as well. Various hybrid strategies utilize blending functions dependent on the molecular Prandtl number, which do not necessarily provide a smooth transition from the viscous/conductive sub-layer to the logarithmic region [2]. This work relies on the k-ζ-f turbulence model [3] and the underlying hybrid wall treatment [4], which is capable of predicting the near-wall momentum and heat transfer with more fidelity, compared to the standard or low-Re variants of the k-ε turbulence model. Based on a new DNS database for turbulent flow and heat transfer in a heated pipe (Re_tau=360, Pr=1, 10, and 20) [1], the RANS-based modelling of the near-wall heat transfer has been improved with respect to accuracy and mesh independence. The potential of the proposed model in real engineering applications is demonstrated in the cooling of electric/hybrid powertrain components (e-motor and power electronics) featuring flows at high Prandtl numbers. [1] Irrenfried, C. and Steiner, H. (2016): DNS of a turbulent heated pipe flow at high Prandtl numbers revisiting the P-function model. 11th International Ercoftac Symposium on Engineering Turbulence Modelling and Measurements (ETMM11), Palermo (Italy), September 21-23, 2016 [2] Šarić, S., Basara, B., and Žunič, Z. (2016): Advanced near-wall modeling for engine heat transfer, Int. J. Heat and Fluid Flow, article in press, http://dx.doi.org/10.1016/j.ijheatfluidflow.2016.06.019 [3] Hanjalić, K., Popovac, M., and Hadžiabdić, M. (2004): A robust near-wall elliptic relaxation eddy-viscosity turbulence model for CFD. Int. J. Heat and Fluid Flow, Vol. 25, pp. 1047-1051 [4] AVL List GmbH (2014): Main Program, FIRE® version 2014 manual, Graz, Austria
Also in:
  • SAE International Journal of Engines - V126-3EJ
  • SAE International Journal of Engines - V126-3
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