Impingement cooling is a well-established technique to reduce the thermal load of hot gas components in gas turbines. Although the technique is widely used, correlations are nonetheless the standard design method, as the flow field and heat transfer are notoriously difficult to predict with state-of-the-art commercially viable CFD calculations. The primary challenges to CFD are phenomena such as shear layers and crossflow interactions. Therefore, a demand for spatially highly resolved measurements exists.
An experimental investigation of a confined row of round jets impinging on a flat surface representative of gas turbine geometries with and without an initial crossflow has been conducted. The effect of the distance between the impingement plate and the target surface as well as the effect of the crossflow flow rate on the interaction of the jets with each other and with the crossflow are assessed. The three-dimensional impingement flow field and the heat transfer characteristics on the target surface are measured. The former has been visualised by Magnetic Resonance Velocimetry (MRV). This measurement technique is relatively novel for engineering applications, but very well suited for low-Mach number flows in complex geometries. It yields millions of measurement points and is thus ideal for a comparison with CFD. The local Nusselt number distribution is obtained using steady-state Thermochromic Liquid Crystals (TLC) on the same test set-up. Secondary losses and errors associated with this method are evaluated by means of an energy balance.
The experiments are accompanied by a CFD simulation using an approach typically used for designing impingement configurations in industry as well as a more advanced method.