The high pressure turbine nozzle guide vane of a modern aeroengine experiences large heat loads and thus requires both highly effective internal and external cooling. This can be accomplished with double-wall effusion cooling, which combines impingement, pin-fin and effusion cooling. The combination of three cooling mechanisms causes high pressure losses, increasing potential for the migration of coolant towards low pressure regions, subsequently starving effusion holes on the leading edge of coolant supply. This paper presents a low order flow network model to rapidly assess the pressure and mass flow distributions through such cooling schemes for a flexible set of geometric and flow conditions. The model is subsequently validated by a series of experiments with varying mainstream pressure gradients. Results from the model are used to indicate design parameters to reduce the effect of coolant migration, and to minimise the risk of destructive hot gas ingestion.
Quasi-transpiration cooling schemes such as Double-Wall Effusion Cooling allow the Nozzle Guide Vanes of High Pressure Turbines in modern aeroengines to experience high heat loads whilst maintaining acceptable temperatures. The combination of impingement, pin-fin and effusion cooling in such schemes produces a high convective cooling efficiency, but this is accompanied by large pressure losses that increase vulnerability to coolant migration toward low pressure regions. This can have severely detrimental effects on cooling performance as effusion holes around the Leading Edge can be starved of coolant, producing no local film cooling protection. This paper presents a Low Order Model (LOM) which rapidly produces pressure, temperature, mass and heat flow distributions throughout Double-Wall Effusion Cooling Schemes, developed from a previously presented Mass Flow Network LOM. These can be found for a variety of flow and geometric conditions, allowing fast analysis of cooling designs. Experiments were conducted using a steady-state facility, from which results were used to validate the new LOM to a satisfactory standard. Using specifically derived dimensionless groups for coolant migration, results from the LOM demonstrate the effect of heat transfer on it as well as the effects of coolant migration on the cooling performance, highlighting design guidelines to reduce such effects and to optimise the component life.
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