The flow through turbopumps is characterized by highly unsteady phenomena at part load conditions, involving large separation and generation of vortical structures. This behavior is strongly dependent on the interaction between rotating and steady parts, which is significantly modified, compared to the one at the design flow rate. Therefore, at off-design conditions, eddy-resolving computations are more suitable to analyze the complex physics occurring inside turbomachinery channels. In this work the large eddy simulation (LES), coupled with an immersed-boundary (IB) method, is utilized to study a mixed-flow pump at a reduced flow rate, equivalent to 40% of the nominal one. The present approach has been already validated in a previous study, where a satisfactory agreement with two-dimensional (2D) particle image velocimetry (PIV) experiments has been shown at design conditions. In this paper a comparison with the LES results at the optimal flow rate is also proposed, in order to understand the important modifications of the flow occurring at part loads.

Turbopumps operating at reduced flow rates experience significant separation and backflow phenomena. Although Reynolds-Averaged Navier–Stokes (RANS) approaches proved to be usually able to capture the main flow features at design working conditions, previous numerical studies in the literature verified that eddy-resolving techniques are required in order to simulate the strong secondary flows generated at reduced loads. Here, highly resolved large-eddy simulations (LES) of a radial pump with a vaned diffuser are reported. The results are compared to particle image velocimetry (PIV) experiments in the literature. The main focus of the present work is to investigate the separation and backflow phenomena occurring at reduced flow rates. Our results indicate that the effect of these phenomena extends up to the impeller inflow: they involve the outer radii of the impeller vanes, influencing significantly the turbulent statistics of the flow. Also in the diffuser vanes, a strong spanwise evolution of the flow has been observed at the reduced load, with reverse flow, located mainly on the shroud side and on the suction side (SS) of the stationary channels, especially near the leading edge of the diffuser blades.

This paper deals with a sufficiently complete analysis of flow forces acting on spools of hydraulic directional control valves. The analysis performed, using the very reliable and commercially widespread “Fluent” code, aims to describe global parameters in order to evaluate such forces with a reasonable accuracy and without performing expensive three-dimensional calculations. To this aim, different fluid dynamics analyses have been carried out inside the valve, starting from simple axis-symmetric models, up to full three-dimensional simulations. A comparison of the 2D and 3D results is then presented.