Prediction and augmentation of nozzle guide vane film cooling hole pressure margin

Authors

Nicholas Edwin Holgate - Department of Engineering Science, University of Oxford
Irene Cresci - Department of Engineering Science, University of Oxford
Peter Thomas Ireland - Department of Engineering Science, University of Oxford
Anthony John Rawlinson - Rolls-Royce plc

Abstract

To ensure adequate cooling and avoidance of hot gas ingestion, a high pressure turbine nozzle guide vane must maintain a safe pressure margin by which the film coolant static feed pressure exceeds the hot gas total pressure. This pressure margin is lowest for cooling holes near the stagnation region, especially near the coolant inlet. This study investigates an insert device which increases the pressure margin in these ingestion risk regions by altering the coolant passage geometry, potentially allowing engine performance gains via reduced combustor pressure loss requirements. Seven parametrically varied inserts are compared within a pressure-tapped, cooled vane model, and design rules are suggested. For correctly designed inserts, pressure margin results show significant improvement in the ingestion risk region, without causing ingestion risks elsewhere. An analytical model of combined converging, diverging and prismatic coolant channels is validated by experimental data to be capable of accurately predicting coolant pressure margins.