A Novel Looped-Freezing Mean Detached Eddy Simulation (DES) Based Approach to Evaluate Underhood Cooling Performance of Commercial Vehicles

A novel looped-freezing mean approach based on Detached Eddy Simulation (DES) approach is developed in context of assessing underhood cooling performance in heavy-duty vehicles. The method involves computing a temporally averaged flow field from DES simulations, which is then frozen and used by the energy solver to predict temperature distributions. This process is iteratively repeated until a statistically steady-state temperature field is achieved. It is demonstrated that traditional DES approach demonstrates superior accuracy in capturing forced convection heat transfer compared to the Reynolds-Averaged Navier–Stokes (RANS) method. The validation against experimental data for flow over a heated sphere at a Reynolds number of 105 shows that DES yields Nusselt numbers with better correlation than RANS. However, it is observed that DES approach captures unsteady flow features that introduce temporal fluctuations in heat transfer. In the context of underhood cooling evaluations where properties of the fluid are strong functions of temperature and coupled with iterative processes such as dual-stream heat-exchanger modeling, these instabilities can frequently lead to numerical divergence of the simulation. The novel looped-freezing mean DES method is then applied to a reduced underhood model, including the heat exchanger and fan assembly, bounded by walls representing adjacent vehicle components. The study show that the novel looped-freezing mean DES approach provides stable and converged thermal predictions for the reduced underhood model. This approach is particularly beneficial for simulations involving highly transient flow fields coupled with thermal phenomena, enabling accurate and reportable temperature evaluations in critical regions.