International Journal of Turbomachinery, Propulsion and Power

The accurate, high-fidelity modeling of moving geometries involving translation and rotation is important in fluid mechanics applications, particularly turbomachinery. These simulations facilitate the analysis of various turbomachinery stages, where complex movements are integral to their functionality. We integrated a sliding mesh capability into the iLES/DNS compressible Navier–Stokes solver within Nektar++, which is a spectral/hp element open-source framework. Static and moving regions of the finite element mesh are coupled across a non-conformal interface using a point-to-point interpolation method (PTPM). The solver is verified on two canonical benchmarks, the isentropic vortex and Couette flow, and validated on the T106A low-pressure turbine cascade with an upstream translating bar that generates inflow wakes, emulating rotor–stator interaction. This paper aims to provide robust validation of the new solver developments and supply a tool to understand how the upstream bar motion influences the downstream blade efficiency, which is crucial for enhancing turbomachinery design and performance.

Safety, profitability, as well as energy and resource efficiency of hydropower plants require, among others, appropriate operation of hydraulic turbines, which involves reliable estimation and monitoring of water flow rate. In this work, computer simulation is used for investigation of water flow through the spiral casing of a hydraulic turbine under real operating conditions. The wall pressure at the pre-defined monitoring points in a radial plane, such as used in the Winter–Kennedy measurement method, is calculated for a range of water flow rates. The choice of the boundary-condition type downstream of the stay vanes and sensitivity to adopted turbulent-flow approach are also investigated. The numerical results agree well with the reference measurements. A relation is established between the computed monitoring pressure difference and the corresponding incoming flow rate. Having measured the static pressure at the given points, it can be used for continuous estimation of the water flow rate in the turbine under actual operating conditions.

This paper presents a numerical investigation of the effect of rotational speed on the development of leakage flow in a low-speed axial fan equipped with a rotating shroud. Rotor deformation induced by centrifugal forces and aerodynamic loading is taken into account through a one-way coupling between steady CFD simulations and static FEM analyses. Aerodynamic and structural results obtained at four rotational speeds are validated against available experimental data collected by the same research group, and the different leakage flow patterns associated with rotor deformation are correctly reproduced. Subsequently, the deformed geometries corresponding to two rotational speeds and operating at the same non-dimensional flow coefficient are used to perform URANS simulations. The numerical results provide insight into the leakage flow behavior within the gap between the rotating shroud and the stationary casing, a region that cannot be experimentally investigated due to optical access limitations. It is shown that the leakage flow rate through the gap shows limited sensitivity to rotor deformation, as it scales with rotational speed, and it is fed by two main contributions: a flow directly extracted from the rotor outlet and a recirculating flow developing along the mounting panel. Conversely, the non-dimensional angular momentum flow rate is larger at the lower rotational speed, corresponding to the case in which the leakage flow is rapidly re-ingested by the rotor. This indicates that the centrifugal effects associated with the leakage flow swirl are not responsible for the observed change in leakage flow pattern. Finally, significant periodic and non-periodic components are identified within the leakage flow. These components are expected to contribute to the formation of the large-scale structures impinging on the rotor blades and thus generating significant noise.