Reassessment of the Conventional: Numerical Validation of a 1D model for the Prediction of Volute Losses

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Abstract The traditional one-dimensional (1D) method for predicting losses in a centrifugal compressor volute relies on simple assumptions. However, it is questionable how accurately these assumptions capture the complex flow physics. This study evaluates these 1D predictions using a comprehensive database of CFD calculations for a standalone volute. In these simulations, the diffuser width and inlet conditions were varied to separately analyze the effects of flow angle and flow rate, allowing for a complete assessment of the volute's loss map. Similar to the 1D predictions, the CFD-predicted total pressure losses in the volute's two subcomponents (the scroll and the conical diffuser) are assigned to the respective velocity components at the volute inlet. This allows for validation of the 1D model against CFD results across the volute's entire operating range. The results show that the radial velocity loss coefficient varies significantly, challenging the 1D assumption of a constant value. In contrast, the tangential velocity loss coefficient in the scroll aligns well with CFD results, showing high loss coefficients at high matching coefficients and decreasing towards low matching coefficients. Losses in the conical diffuser depend on both the matching coefficient and the inlet flow angle, contrary to 1D model assumptions. While the 1D model satisfactorily predicts the global loss coefficient characteristics, it generally overestimates losses. Additionally, the CFD results reveal that the matching coefficient for minimum global losses varies with the flow angle, a factor not considered by the 1D model, indicating its limitations for volute matching assessment.