International Journal of Turbomachinery, Propulsion and Power

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.

This paper presents methods and results on optimizing the functionality of pressurized sewerage systems, specifically wastewater pumping stations. A holistic approach is introduced to address major issues in wastewater transport such as sedimentation in suction chambers and fiber-induced issues in wastewater pumps, as well as their effects and detection. A conceptual suction chamber is scaled using hydraulic similarity and is experimentally investigated regarding its susceptibility to sedimentation. Optimization of inlets and manifolds, pumps, and sloped walls contribute to minimizing sedimentation. In terms of wastewater pumps, a semi-open two-channel wastewater impeller is optimized for its efficiency via response surface optimization. The subsequent optimization for functionality showcases the nexus of the two characteristics by means of cut-back and thickened leading edges, which significantly reduce the susceptibility to clogging. Another important consideration in wastewater pump design is the back shroud cavity. Through iterative experiments with different housing recess configurations, the back shroud cavity is optimized to minimize fiber entry and protect the mechanical seal. Lastly, the demonstration of the effects of clogging in the form of transient instationarities in the torque of a wastewater pump underline the importance of optimizing wastewater pumps for their functionality and low susceptibility to clogging.

This paper presents an application and validation case for the recently obtained variational principle of a shock stationed in a duct. The streamline curvature method for the circumferentially averaged through-flow and blading design inverse problem remains fundamentally used in current axial compressor design systems and is indispensable as the generator of multi-stage blade coordinates. However, this method inherently smoothens flow discontinuities and thus, to date, cannot provide the stage stall margin, the key performance indicator most critical in the adjustment of high-loading stages, requiring instead a time-consuming CFD validation afterward. Leveraging the variational principle for shock stationarity, this paper acquires a method to show efficiently the stage stall margin by visualizing rotor passage shock rapidly. In the general coaxial rotating relative motion, by modeling the transonic streamlines as a set of layered quasi-one-dimensional duct flows, a variational principle of flow impulse potential energy for the stationary normal shock is derived. It is found that the factors governing the stationarity and location of the normal shock in relative motion include the variable cross-sectional area, the frictional and other on-way losses, and the variable rotational radius of the duct flow. In the applications to transonic rotor cascades, the frictional and other on-way losses are prescribed. First, the discontinuous entropy generation distributions along the cascades of each transonic layer are set to consider the boundary layer, oblique shock, normal passage shock, shock–boundary layer interference, and trailing edge losses. Second, with the total streamline loss fixed by the through-flow design, all shock locations possessing positional stability are determined via the variational principle for each streamline. Third, by comparing with CFD direct problem resu lts, a dimensionless rule governing the actual entropy generation distribution along the layer cascades is established. In three kinds of design cases of axial compressor stage, this method yields consistently 3D curved-surface structures of passage shock that agree well with CFD direct problem solutions, demonstrating its effectiveness and a certain applicability.