Estimating the Heat Transfer Coefficient for a Jet Impingement Tube with the Initial Cross Flow

Jet impingement, one of the highly efficient heat exchange enhancement methods, is commonly used to cool down the nozzle guide vanes (NGVs) of gas turbine engines. This method normally generates a very high local heat transfer coefficient (up to 1,000 ÷ 3,000 W/m²) due to the presence of a high turbulent kinetic energy region and a laminar-to-turbulent transition zone created by the jet. In the jet impingement system, the edge tip zone of a turbine vane is often represented by cylindrical models, while flat plate models are adopted for the midchord region. Due to interactions between the jet flow and the initial cross flow at the midchord region, the local heat transfer coefficient increases remarkably. The heat transfer coefficient can be determined through computational fluid dynamics (CFD) simulation or experimental approaches. Available experimental methods in the current literature include the steady-state technique, transient liquid crystal thermography technique, and temperature oscillation technique (TOIRT). In this article, a CFD model in ANSYS-Fluent and a TOIRT experimental system were developed to determine the heat transfer coefficient for a jet impingement tube with initial cross flow. The numerical model was validated by experimental results obtained in this study along with other data reported in the literature. The results show that the cross flow increases the average and maximum heat transfer coefficients in the jet impingement model. However, the cross flow also significantly changes the direction of the jet flow and the position of the stagnation zone.