Unsteady Interaction Effects on a Transitional Turbine Blade Boundary Layer

Abstract

Results are presented illustrating the detailed behavior of the suction surface boundary layer of a transonic gas turbine rotor in a two-dimensional cascade under the influence of both free-stream turbulence and simulated nozzle guide vane wakes and shocks. The instrumentation included thin film resistance thermometers along with electrical analogues of the one-dimensional heat conduction equations to obtain wide bandwidth heat transfer rate measurements in a short duration wind tunnel. This instrumentation provides sufficient time resolution to track individual wake and shock-related events and also the turbulent bursts of a transitional boundary layer. Wide bandwidth surface pressure transducers and spark Schlieren photography were used in support of these heat transfer measurements. The results showed a direct relationship between the passage of wake disturbances and transient surface heat transfer enhancements. It was possible to track both wake and transitional events along the surface and to compare these with the expected convection rates. Analysis of the signals allowed direct calculations of intermittency factors, which compared well with predictions. Additional effects due to a moving shock/boundary layer interaction were investigated. These resulted in marked variations in heat transfer rate both above and below the laminar values. These excursions were associated with separation and re-attachment phenomena.