The flow field in a high pressure ratio centrifugal compressor with a vaneless diffuser has been investigated numerically. The main goal is to assess the influence of various turbulence models suitable for internal flows with an adverse pressure gradient. The numerical analysis is performed with a 3D RANS in-house modified solver based on an object-oriented open-source library. According to previous studies from varying authors, the turbulence model is believed to be the key parameter for the discrepancy between experimental and numerical results, especially at high pressure ratios and high mass-flow. Particular care has been taken at the wall, where a detailed integration of the boundary layer has been applied. The results present different comparisons between the models and experimental data, showing the influence of using advanced turbulence models. This is done in order to capture the boundary layer behavior, especially in large adverse pressure gradient single stage machinery.
The flow field in a high pressure ratio centrifugal compressor with vaneless diffuser has been investigated numerically. Main goal is to assess the influence of various turbulence models suitable for internal flows with adverse pressure gradient. The numerical analysis is performed with a 3D RANS in-house modified solver based on an object-oriented open-source library. According to previous studies from varying authors, the turbulence model is believed to be the key parameter for the discrepancy between experimental and numerical results, especially at high pressure ratios and high mass-flow. Particular care has been taken at the wall, where a detailed integration of the boundary layer has been applied. The results presents different comparisons between the models and experimental data showing the influence of using advanced turbulence models. This is done in order to capture the boundary layer behavior, especially in large adverse pressure gradient single stage machinery.
The focus of this paper lies on the leakage flow across the shroud of a centrifugal compressor impeller. It is common practice to use shrouded impellers in multi stage compressors featuring a single shaft. The rotating impeller then has to be sealed against the higher pressure in the downstream diffuser by means of labyrinths. The relative amount of leakage is higher for stages designed for low flow, meaning that the associated losses gain in relevance. In addition to this loss source, the injection of the leakage flow has a serious influence on the main flow in a region where it is prone to separation, i.e. at the suction side of the impeller blades close to the shroud, where the highest relative velocities are found. The present paper discusses the numerical results of several geometrical arrangements where the leakage flow was mixed with the main flow in different ways. The distance between the location of injection and the leading edge of the impeller as well as the orientation of the injected flow showed a distinct influence on the performance of the entire stage, mainly on stability.
The three-dimensional turbulent flow in a compact hydraulic machine elbow draft tube is numerically investigated for several operating conditions, covering an extended range around the best efficiency point. Comparisons with the experimental data are presented as validation. The interest is focused on the experimentally observed pressure recovery drop occurring near the best efficiency point. The flow is first analyzed locally by means of a topological analysis, then globally with an energetic approach. The study provides evidence for the role played by a Werle´-Legendre separation originating in the bend. The separation is due to the contrasting flow angles imposed by the blades, and the angle resulting from the secondary flow.
This paper describes the development and validation steps of a characteristics-based explicit along with a novel fully implicit mixing plane implementation for turbomachinery applications. The framework is an unstructured 3D RANS in-house modified solver, based on open-source libraries. Particular attention was paid to mass-conservation, accurate variables interpolation, and algorithm stability in order to improve robustness and convergence. By introducing a specific interface, allowing the use of algebraic multigrid solvers together with multiprocessor computation, a speed up of the numerical solution procedure was achieved. The validation of both mixing plane algorithms is carried out on an industrial radial compressor and a cold air 1.5 stages axial turbine.
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