This experimental investigation reports the convective heat transfer coefficient around the rotor of a transonic turbine stage. Both time-resolved and time-averaged aspects are addressed. The measurements are performed around the rotor blade at 15, 50, and 85% span as well as on the rotor tip and the hub platform. Four operating conditions are tested covering two Reynolds numbers and three pressure ratios. The tests are performed in the compression tube turbine test rig CT3 of the von Karman Institute, allowing a correct simulation of the operating conditions encountered in modern aero-engines. The time-averaged Nusselt number distribution shows the strong dependence on both blade Mach number distribution and Reynolds number. The time-resolved heat transfer rate is mostly dictated by the vane trailing edge shock impingement on the rotor boundary layer. The shock passage corresponds to a sudden heat transfer increase. The effects are more pronounced in the leading edge region. The increase of the stage pressure ratio causes a stronger vane trailing edge shock and thus larger heat transfer fluctuations. The influence of the Reynolds number is hardly visible.

The efficiency of a cooled transonic turbine stage was measured in a compression tube facility. The formulation takes into account mechanical losses, coolant flows and leakage flows. The proposed methodology allows computing the efficiency independently from the test rig. Owing to the short testing time (∼0.5 s), specific measurement and data reduction techniques are used. The paper details how the power, the overall mass flow, the mass-averaged inlet quantities and the stage pressure ratio are determined. The measurements of mechanical losses and of the thermodynamic properties of coolant and leakage flows are also described. Finally, results are presented and supported by an uncertainty analysis that identifies the random and systematic contributions to the final error.

Due to the transient operation of short duration facilities (0.2–1.0s running time), fidelity in temperature reproduction requires both minimum steady-state errors and a frequency response above 20Hz. Even with the smallest thermocouple wire diameter (∼12μm), badly designed probes may suffer from unsteady heat conduction between wires and supports. The resulting error is often much larger than steady errors such as the effect of recovery factor. In this paper, the origins of steady and unsteady measurement errors are described and evaluated. An analytical modeling of the transient convection/conduction problem is presented. A number of probe designs are described and evaluated at different Reynolds number. The dynamic response is tested in a hot jet apparatus that generates temperature steps, with jet velocities up to 150m/s. The influence of the length/diameter ratio, the type of support and the presence of a shield on the dynamic response are addressed. The unsteady behavior of a thermocouple probe can be replicated with a combination of first order systems, which defines the transfer function of the probe. The relevant parameters are found by using an optimization routine that fits the numerical system response to the experimental response. This numerical model can be reversed to perform a frequency compensation of the measured data.

This experimental research investigates the influence of the hub endwall cavity flow on the aerodynamics and heat transfer of a high-pressure transonic turbine stage tested under engine representative conditions. The measurements include the hub and tip endwall static pressure downstream of the vane, the static pressure and heat transfer on the rotor blade at 15% span and on the hub platform as well as the stage downstream total pressure and temperature. Both steady and unsteady aspects are addressed. The hub endwall cavity flow has a significant influence on both the time-averaged and time-resolved components of the measured quantities. The effects are shown to be mainly due to an increase of the pitchwise averaged static pressure at hub downstream of the vane when cavity flow ejection is activated.

This paper presents steady and unsteady pressure measurements at three span locations (15, 50 and 85%) on the rotor surface of a transonic turbine stage. The data are compared with the results of a 3D unsteady Euler stage calculation. The overall agreement between the measurements and the prediction is satisfactory. The effects of pressure ratio and Reynolds number are discussed. The rotor time-averaged Mach number distribution is very sensitive to the pressure ratio of the stage since the incidence of the flow changes as well as the rotor exit Mach number. The time-resolved pressure field is dominated by the vane trailing edge shock waves. The incidence and intensity of the shock strongly varies from hub to tip due to the radial equilibrium of the flow at the vane exit. The decrease of the pressure ratio attenuates significantly the amplitude of the fluctuations. An increase of the pressure ratio has less significant effect since the change in the vane exit Mach number is small. The effect of the Reynolds number is weak for both the time-averaged and the time-resolved rotor static pressure at mid-span, while it causes an increase of the pressure amplitudes at the two other spans.