Approximating Convective Boundary Conditions for Transient Thermal Simulations with Surrogate Models for Thermal Packaging Studies

The need for transient thermal simulations in vehicle packaging studies has grown rapidly in recent years. To date, the computational costs associated with the transient simulation of 3D conjugate heat transfer phenomena has prohibited the widespread use of full vehicle transient simulations. This paper presents results from a recent study that explored a method to circumvent the computational costs associated with long transient conjugate heat transfer simulations.

The proposed method first segregates the thermal structural and fluid physics domains to take advantage of time scale differences. The two domains are then re-coupled to calculate a series of steady state conjugate heat transfer simulations at various vehicle speeds. The local convection terms are then used to construct a set of surrogate models dependent on vehicle speed, that predict the local heat transfer coefficients and the local near wall fluid temperatures. These surrogate models are then coupled to the thermal structural simulation to simulate the wall temperature history.

Results from transient conjugate heat transfer simulations of several vehicle test cycles were compared to simulations performed with the method described above. Differences in predicted wall temperatures were evaluated to assess the overall accuracy of the proposed methodology. Heat transfer coefficients and fluid temperatures predicted by the surrogate models were also compared to the local heat transfer coefficients and fluid temperatures calculated by the transient conjugate heat transfer simulation. It is concluded that surrogate models can be used to reduce the computational costs associated with transient thermal simulations with an acceptable loss of accuracy for the evaluated test cycles.