Effect of turbulence modeling for the prediction of flow and heat transfer in rotorcraft avionics bay

Abstract

In this paper, four turbulence models are compared on the basis of the predictions they produce for the flow and heat transfer in the avionics bay area of a rotorcraft. The turbulence models studied are the standard k-ε, Renormalization Group (RNG) k-ε, realizable k-ε, and Shear-Stress Transport (SST) k-ω model. The avionics bay used in the study houses avionics equipment mounted on the floor and on a rack inside the bay to mimic a realistic distribution of equipment in actual rotorcraft. The avionics bay incorporates a cooling system consisting of a fan that intakes ambient air via a forced-convection method and an exhaust, with the purpose of keeping the avionics equipment temperatures below their operational limits. The turbulence levels, flow and thermal fields are investigated and compared in order to quantify the differences between the predictions of the turbulence models used in computations. It is observed that the use of the standard and realizable k-ε models mostly produce similar flow and thermal results across the bay area, while the largest differences between the predictions are found with the RNG k-ε and the SST k-ω turbulence models especially at the locations in the vicinity of the fan impingement. Comparing the avionics equipment surface temperature predictions, the standard and realizable k-ε turbulence models are observed to produce slightly more conservative results. The average variation between the surface temperature predictions by all models is less than 3.5 K, indicating that this parameter is considerably insensitive to the selected turbulence model. A close examination of the fan jet region starting from the fan inlet revealed generally similar predictions of flow and thermal features by all turbulence models. The maximum variation in the velocity and temperature predicted by all turbulence models is 2.2% and 0.1% of the fan inlet conditions, respectively. Large differences in turbulence intensity were observed depending on the location downstream of the fan jet and the turbulence model used.