Designs for future aero engines aim for increased efficiency with reduced exhaust gas and noise emissions. To achieve these goals, comprehensive physical understanding and highly innovative solutions are necessary. Even though computational capabilities are rising, the required confidence level is restrained. To understand and validate theoretical and numerical models, extensive experiments at realistic operating conditions are crucial. The modular compressor at the Transonic Compressor Darmstadt test facility at Technical University of Darmstadt enables investigations of prototype BLISK rotors in single or 1.5-stage setups, operating at high-speed conditions. Extensive steady and time-resolving instrumentation is used to determine the compressor aerodynamics and performance as well as aeroelastics. To foster improvements in numerical modelling and predictability based on high quality experimental data, the TUDa-GLR-OpenStage test case is introduced. It comprises a single stage setup, including the BLISK rotor, a 3D-optimized stator as well as the annulus contour. The data set is supplemented with comprehensive measurement data at stage inlet and outlet as well as running tip clearances. This paper describes the open test case, related geometries, measurement procedures and corresponding experimental results, including steady state performance and unsteady aerodynamics. Ultimately, it is aiming to provide a standard case for future development of numerical models and comparable validation.

This paper presents a comprehensive validation and verification study of turbomachinery Reynolds-averaged Navier-Stokes flow solvers on the transonic axial compressor TUDa-GLR-OpenStage. Two commercial solvers namely Ansys CFX and Numeca FineTurbo are adopted to provide the benchmark solutions, which can be used for verification of other RANS solvers in the future. Based on these solvers, five sets of grids, two advection schemes (i.e., central difference and second-order upwind), four turbulence models (i.e., SA, SA-RC, SST and EARSM) and two rotor-stator interface models (i.e., mixing plane and sliding plane) are investigated to quantify their effects on predicting the performance and the flow field of the compressor stage. Results show that the choices of grid density and turbulence model are most sensitive to the prediction, leading to 5% and 7% variation in compressor performance characteristics, respectively. Regarding the choice of grid density, a method to estimate the grid discretization error is demonstrated, which is transferrable to other cases. Regarding the choice of turbulence model, the EARSM model is found overall most accurate among the investigated models, and the limitations and deficiencies of the rest models are discussed in detail based on the analysis of the mean flow fields and the eddy viscosity fields. The grids and the major CFD results presented in this work are open-accessed to the community for further research. The results and discussions presented in this paper provide a useful reference for future practices of RANS simulations for compressors.

Reynolds-averaged Navier–Stokes (RANS) simulations currently serve as the prevailing industrial method for simulating axial compressor flows, and this status is expected to persist in the foreseeable future. To evaluate the capabilities of contemporary RANS solvers for compressors, this article presents a statistical analysis of RANS simulation results submitted to the first and the second Global Power and Propulsion Society (GPPS) computational fluid dynamics (CFD) workshops, where blind tests on the TUDa-GLR-OpenStage transonic axial compressor were performed. The workshops were held online in December 2021 and in a hybrid format at Chania, Greece, in September 2022, which are the first primary turbomachinery CFD workshops following the 1994 International Gas Turbine Institute (IGTI) CFD blind test event on NASA Rotor 37. A total of 35 submissions were received from 12 distinct RANS solvers, contributed by 14 participants affiliated with 11 organizations across 5 countries. Participants include academic researchers, engineers from the turbomachinery industry, and developers of commercial CFD solvers. First, the grid convergence behavior exhibited by various solvers employing different turbulence models is examined. Afterward, the prediction accuracy of the ensemble of the simulation results is evaluated, and the representative simulation results are compared and analyzed in detail. The key factors that improve the prediction accuracy are identified. These results foster improved usage and further development of turbomachinery RANS solvers.

The future trend of clean sky aviation has led to a smaller core engine, resulting in highly loaded stages with increased relative tip gaps and leakage flows, which causes a reinforced influence of secondary flow phenomena. This article experimentally investigates the secondary flow effects in the 3D-optimized shrouded stator of the TUDa-GLR-OpenStage, representative of a transonic high-pressure compressor front stage, and its susceptibility to typical hub leakage flows. The impact of stator hub leakage on efficiency and total pressure ratio is investigated for several operating speeds, from subsonic to nominal transonic operating conditions. Steady five-hole probe and time-resolved virtual multi-hole probe measurements at different operating conditions at nominal speed are conducted to investigate the underlying loss mechanisms. The leakage mass flow is determined using the measured pressure difference within the fin seal. Steady results show that the optimized 3D stator effectively suppresses the hub corner separation compared to the predecessor 2D stator, but its performance is further limited by a near-tip separation. With the increased stator hub leakage (at a leakage-to-main flow ratio of about 0.4%), the compressor isentropic efficiency generally drops (by about −0.5%) at the full operating range due to an enhanced hub corner separation effect. However, the increased leakage also helps alleviate the tip-corner separation when operating near stall, leading to a smaller efficiency penalty under these conditions. Unsteady results reveal the sensitivity of transient compressor performance to the passing rotor wake, but limited interaction between this phenomenon and the increased leakage is observed. These findings provide insight into the stator hub leakage-related penalties on the compressor aerodynamics efficiency.

This paper experimentally investigates a highly-loaded 1.5-stage transonic axial compressor, which comprises a variable inlet guide vane, a BLISK rotor, and a variable stator in tandem arrangement. A detailed comparison between the newly designed compressor stage and a reference stage with a conventional stator design was conducted by using extensive instrumentation. Thus, steady and unsteady phenomena—focusing on the aerodynamic and aeroelastic behavior—were analyzed. Due to the new stator vane design, a higher aerodynamic stator vane loading was pursued, while the vane count was reduced. This, in turn, allowed a rotor design with an increased work coefficient. This experimental study revealed several effects of the optimized compressor stage in terms of both performance and the corresponding aerodynamics, as well as the aeroelastic behavior.

The hub and casing walls of axial compressors are often modeled as smooth continuous surfaces in CFD simulations, but in real geometries, non-smooth pinches, steps and leakage cavities may exist. In the GPPS first Turbomachinery CFD Workshop, a comprehensive validation and verification campaign...