The objective of the presented work is to perform numerical and experimental studies on compressor stators. This paper presents the modification of a baseline stator design using numerical optimization resulting in a new 3D stator. The Rolls Royce in-house compressible flow solver HYDRA was employed to predict the 3D flow, solving the steady RANS equations with the Spalart-Allmaras turbulence model, and its corresponding discrete adjoint solver. The performance gradients with respect to the input design parameters were used to optimize the stator blade with respect to the total pressure loss over a prescribed incidence range, while additionally minimizing the flow deviation from the axial direction at the stator exit. Non-uniform profile boundary conditions, being derived from the experimental measurements, have been defined at the inlet of the CFD domain. The presented results show a remarkable decrease in the axial exit flow angle deviation and a minor decrease in the total pressure loss. Experiments were conducted on two compressor blade sets investigating the three-dimensional flow in an annular compressor stator cascade. Comparing the baseline flow of the 42° turning stator shows that the optimized stator design minimizes the secondary flow phenomena. The experimental investigation discusses the impact of steady flow conditions on each stator design while focusing on the comparison of the 3D optimized design to the baseline case. The flow conditions were investigated using five-hole probe pressure measurements in the wake of the blades. Furthermore, oil-flow visualization was applied to characterize flow phenomena. These experimental results are compared with the CFD calculations.

This investigation discusses the impact of a non-steady outflow condition on the compressor stator flow in an annular cascade which is periodically chocked through a rotating disc in the wake, to simulate the expected conditions for a pulsed detonation engine (PDE). A 2D controlled diffusion airfoil of the highly loaded linear stator cascade by [1] has been transferred to the annular compressor test rig to compare results under non-steady conditions via multi-colored oil flow visualization on the suction side and pressure measurements in the wake of the blades. Three different Strouhal numbers of the choking device are investigated and analyzed by phase averaged pressure measurements downstream of the stator to visualize the unsteady flow characteristics. Triggered by the changed incidence angle due to the choking, separation on the suction side and in the hub region form a periodic event depending on the position of the blockage device. Active flow control (AFC) is implemented by means of side wall actuation at the hub to improve flow conditions. Pressure measurements show that the turning of the blades can be raised and a static pressure rise is gained by the AFC while periodic choking is active.

The efficiency of modern Turbofan engines can be significantly increased by using a gearbox between compressor and turbine of the low pressure section. Rotational speed of the low pressure turbine (LPT) in a Geared Turbofan is much higher than in normal LPT’s which lead to necessary adjustments in blade design. This work has investigated the transition behavior of a modified profile geometry for low-loss at engine cruise conditions. Typical LPT conditions have thus been chosen as baseline for the experimental work. A pressure distribution has been created on a flat plate by means of contoured walls in a low speed wind tunnel. The paper will analyze the experimental results and show additionally the numerical predictions of the test case. The experimental part of this paper describe how the blade was Mach number scaled to obtain the geometry of the wind tunnel wall contour. The pressure distribution for the incompressible test case show a very good agreement to the compressible case. Boundary layer (BL) measurements with hot-wire-anemometry have been performed at high spatial resolution under a freestream turbulence of almost 8%. Different Reynolds numbers have been investigated and will be compared with special attention being paid to the transition on the suction side by contour plots (turbulence levels, turbulent intermittency) and integral BL parameters. It was found that the transition on the suction side is not completed for small Reynolds numbers but takes place at higher velocities. In the numerical part studies by means of steady RANS simulations with k-ω – SST turbulence model and γ-Reθ transition model have been conducted. The aim is to validate the RANS solver for the low-loss LPT application. Hence, comparison is made to the measured data and the transitional behavior of the BL. Furthermore, additional parameter variations have been conducted (turbulence intensity and Reynolds number). The numerical investigations show partially a good comparison for the BL development indicating the different transition modi with increasing Reynolds number and turbulence intensity.

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