This paper presents turbulence measurements and detailed flow analysis in an axial turbine stage. Fast response aerodynamic probes were used to resolve aperiodic fluctuations along the three directions. Assuming incompressible flow, the effective turbulence level and Reynolds stress are retrieved by evaluating the stochastic velocity component out of the measured time-resolved pressure and flow angle fluctuations along the streamwise, radial, and circumferential direction. A comparison between turbulence intensity and measured total pressure shows that flow structures with higher turbulence level are identified in the region of loss cores at the exit of the second stator passage. Turbulence intensity is evaluated under isotropic and nonisotropic assumption in order to quantify the departure from isotropic conditions. The measurements show that locally the streamwise fluctuating component can be twice bigger than the radial and tangential component. The current analysis shows that multisensor fast response aerodynamic probes can be used to provide information about the mean turbulence levels in the flow and the Reynolds stress tensor, in addition to the measurements of unsteady total pressure loss. Nomenclature c = absolute velocity vector e = mean unit vector in the secondary flow definition p = static pressure p d = dynamic head s, , r = streamwise, circumferential, and radial directions T=T 0 = blade passing period fraction t = time u = streamwise velocity component u,ṽ,w = periodic velocity component: phase-lock averaged u 0 , v 0 , w 0 = stochastic (aperiodic) velocity components v = circumferential velocity component w = radial velocity component = yaw angle = pitch angle x = absolute uncertainty of quantity x = density Subscripts/superscripts 1 = probe position 1 iso = isotropic assumption NS = nonsimultaneous sec = secondary flow vector

Propeller performance is traditionally represented by a performance map that gives propeller efficiency as a function of the flight Mach number, the power coefficient C P , and the advance ratio J. This work aims to demonstrate how this map changes when the design C P and J change and to propose a novel map format that is able to capture the performance of different propeller designs. For this purpose, the propeller performance is simulated using a propeller lifting-line method validated for the SR3 propfan. Subsequently, the propeller model is used within a sequential quadratic programming framework to optimize the blade twist and chord distribution for different sets of design C P and J. A complete propeller performance map is then generated for each one of the optimized designs. The results demonstrate that all the investigated propellers can be modeled by a common map, which determines separately the ideal efficiency and the viscous losses. The ideal efficiency is given in the traditional format of η i fC P ;J, whereas the viscous losses are represented as a function of the relative variables C P ∕C Pdes and J∕J des .

This paper presents an experimental investigation of a novel approach for controlling the rotor tip leakage and secondary flow by injecting cooling air from the stationary casing onto the rotor tip. It contains a detailed analysis of the unsteady flow interaction between the injected air and the flow in the rotor tip region and its impact on the rotor secondary flow structures. The experimental investigation has been conducted on a one-and-1/2-stage, unshrouded turbine, which has been especially designed and built for the current investigation. The turbine test case models a highly loaded, high pressure gas turbine stage. Measurements conducted with a two-sensor fast-response aerodynamic probe have provided data describing the time-resolved behavior of flow angles and pressures, as well as turbulence intensity in the exit plane of the rotor. Cooling air has been injected in the circumferential direction at a 30 deg angle from the casing tangent, opposing the rotor turning direction through a circumferential array of ten equidistant holes per rotor pitch. Different cooling air injection configurations have been tested. Injection parameters such as mass flow, axial position, and size of the holes have been varied to see the effect on the rotor tip secondary flows. The results of the current investigation show that with the injection, the size and the turbulence intensity of the rotor tip leakage vortex and the rotor tip passage vortex reduce. Both vortices move toward the tip suction side corner of the rotor passage. With an appropriate combination of injection mass flow rate and axial injection position, the isentropic efficiency of the stage was improved by 0.55 percentage points.

In order to advance the technology for measurements in higher temperature flows, a novel miniature (diameter 2.5 mm) fast response probe that can be applied in flows with temperatures of up to 533 K (500°F) has been developed. The primary elements of the probe are two piezoresistive pressure transducers that are used to measure the unsteady pressure and unsteady velocity field, as well as the steady temperature. Additional temperature and strain gauge sensors are embedded in the shaft to allow a much higher degree of robustness in the use of this probe. The additional temperature sensor in the shaft is used to monitor and correct the heat flux through the probe shaft, facilitating thermal management of the probe. The strain gauge sensor is used to monitor and control probe shaft vibration. Entirely new packaging technology had to be developed to make possible the use of this probe at such high temperatures. Extensive calibration and thermal cycling of the probe used to bind the accuracy and the robustness of the probe. This novel probe is applied in the one-and-1/2-stage, unshrouded axial turbine at ETH Zurich; this turbine configuration is representative of a high work aero-engine. The flow conditioning stretch upstream of the first stator is equipped with a recently designed hot streak generator. Several parameters of the hot streak, including temperature, radial and circumferential position, and shape and size can be independently controlled. The interactions between the hot streak and the secondary flow present a perfect scenario to verify the probe’s capability to measure under real engine conditions. Therefore, measurements with the novel probe have been made in order to prove the principle and to detail the interaction effects with blade row pressure gradients and secondary flows.

This paper presents a study of the three-dimensional flow field within the blade rows of a single stage highpressure axial turbine (low-speed, large-scale). Measurements have been performed in the stationary and rotating frames of reference. Time-mean data have been obtained using five-hole pneumatic probes. The transport mechanisms of the stator wake and passage vortices through the rotor blade row have been studied using smoke flow visualisation. Furthermore, unsteady measurements have been carried out using a three axis hot-wire. Steady and unsteady numerical simulations have been performed using a structured threedimensional Navier-Stokes solver to further understand the blade row interactions. The development of the stator exit flow field through the rotor blade row is described. The path of the stator passage vortices is altered by the rotor secondary flow. The rotor passage vortices are also affected by the transport of the stator secondary flow. The predicted flow field was interrogated from the perspective of loss production. The contribution of the unsteady flow to the stage loss has been evaluated using unsteady numerical simulations. The effect of stator viscous flow transport on the rotor flow angles is also discussed in brief. Finally, a simple model is proposed for the transport of the secondary flow vortices in the downstream blade row based on the understanding obtained from the measurements and numerical simulations.