Influence of inlet flow configuration on the flow field within and around a fan-shaped film cooling hole

This thesis examines the internal flow dynamics of a typical fan-shaped film cooling hole, as found in gas-turbine aero-engines. As design turbine entry temperatures continue to rise in search of greater engine efficiency, effective cooling is required to maintain turbine components at acceptable temperatures and prevent failure. Literature regarding shaped cooling hole investigations, particularly the influence of inlet conditions on cooling hole flows, is reviewed. A general failure to fully quantify inlet conditions and an inconsistent terminology for describing them is noted. This thesis argues for use of an inlet velocity ratio (IVR) defined as the ratio of the coolant passage velocity to the jet velocity, together with additional parameters required to define the velocity distribution in the coolant supply passage. A unique facility has been designed and constructed to conduct large scale testing of film cooling hole geometries. This facility enables independent control of cooling passage velocity and orientation, coolant flow rate, and external cross-flow. Experimental investigations of the internal flow field for a laterally expanded 50 times scale fan-shaped hole are presented. Hot-wire anemometry and pneumatic measurements reveal the extent of separation at the cooling hole inlet and its variation with IVR and coolant passage orientation. Inlet lip separation causes a jetting effect that extends throughout the length of the cooling hole. The exit velocity profiles and turbulence distributions are highly dependent on the IVR. In addition, the effect of blowing ratio between coolant and external cross-flow is investigated through flow field measurements at the hole exit. Computational simulations of limited flow configurations, together with discharge coefficient and axial pressure distribution measurements, enable a complete description of the internal flow dynamics and provide important data for use in cooling system design and validation of numerical simulations.