Direct Simulation of Internal Flow Transient Liquid Crystal Experiments

Abstract

Transient liquid crystal experiments can provide high fidelity heat transfer data for complex geometries, particularly for internal geometries where IR cameras cannot be applied. However, one main drawback of applying the technique to internal geometries is the accurate definition of the driving gas temperature and the need to define it locally in the streamwise direction. Additionally, due to transient changes in the driving gas streamwise profile, the comparison to steady state CFD has been questioned. This paper explores simulating the transient behaviour of the experiment directly. A novel technique to account for differences in the applicable time scales is developed, where the solid surface temperature is calculated analytically using the impulse response method for a semi-infinite conduction and coupled to CFD solver directly. This is compared to the application of transient conjugate heat transfer. Both numerical methods are applied to simulate a transient liquid crystal experiment of a stationary super-scaled rib turbulated internal cooling passage. The surface temperature from the numerical results is post-processed using the method applied in the experiment to ensure direct comparison. Results show that calculations using the new analytical method and steady state gave very similar Nusselt number distributions and mean value in relation to the experimental data. Analysis of transient variation of Nusselt number indicated localised maximum variations up to 40%, though this was not found to significantly effect the minimised global values.