A multiobjective optimization technique based on the computational fluid dynamics (CFD) simulations and the orthogonal test is proposed to reduce the pressure pulsation in this paper. Three levels of four well‐known performance factors L₉ (3⁴) were considered in the orthogonal test scheme: the number of blades, the blade setting angle, the hub ratio, and the distance between the blade and the guide vane. The evaluation indexes corresponded to the head, efficiency, shaft power, and pressure pulsation, respectively. An optimal configuration A₂B₁C₂D₃ was obtained by comprehensive frequency analysis method, after intuitive and range analysis. In comparison with the nonoptimized model, the new design’s head and efficiency increased by 17.8% and 4.26%, whilst the shaft power and the pressure pulsation coefficient reduced by 1.22% and 11%, respectively. Experiments conducted on the optimized pump were consistent with the CFD model. Six different rotational speed conditions in the optimal operating points were numerically calculated in order to explore the internal hydraulic characteristics of the optimized axial flow pump. It is verified that the comprehensive frequency analysis method based on the orthogonal test approach is effective for the multiobjective optimization of the axial flow pump.

This paper performed a numerical study into the dynamic stress improvement of an axial-flow pump and validated the simulation results with a prototype test. To further analyze the dynamic stress characteristics of impeller blades of axial-flow pumps, a bidirectional fluid–structure interaction (FSI) was applied to numerical simulations of the unsteady three-dimensional (3-D) flow field of the whole flow system of an axial-flow pump, and the gravity effect was also taken into account. In addition, real-structure-based single-blade finite element model was established. By using the finite element method, a calculation of the blade’s dynamic characteristics was conducted, and its dynamic stress distribution was determined based on the fourth strength theory. The numerical results were consistent with the prototype tests. In a rotation cycle, the dynamic stress of the blade showed a tendency of first increasing, and then decreasing, where the maximum value appeared in the third quadrant and the minimum appeared in the first quadrant in view of the gravity effect. A method for reducing the stress concentration near the root of impeller blades was presented, which would effectively alleviate the possibility of cracking in the unreliable region of blades. Simultaneously, an experimental method for the underwater measurement of the dynamic stress of prototypical hydraulic machinery was put forward, which could realize the underwater sealing of data acquisition instruments on rotating machinery and the offline collection of measured data, finally effectively measuring the stress of underwater moving objects.

It is important to understand tidal stream turbine performance and flow field, if tidal energy is to advance. The operating condition of a tidal stream turbine with a supporting structure has a significant impact on its performance and wake recovery. The aim of this work is to provide an understanding of turbine submerged depth that governs the downstream wake structure and its recovery to the free-stream velocity profile. An experimentally validated numerical model, based on a computational fluid dynamics (CFD) tool, was present to obtain longitudinal, transverse and vertical velocity profiles. Wake characteristics measurements have been carried out in an open channel at Hohai University. The results indicate that varying the turbine proximity to the water surface introduces differential mass flow rate around the rotor that could make the wake persist differently downstream. CFD shows the same predicted wake recovery tendency with the experiments, and an agreement from CFD and experiments is good in the far-wake region. The results presented demonstrate that CFD is a good tool to simulate the performance of tidal turbines particularly in the far-wake region and that the turbine proximity to the water surface has an effect on the wake recovery.

Labyrinth seals are not usually included in the numerical models of hydraulic machinery to simplify the geometric modeling, and thereby reduce the calculation burden. However, this simplification affects the numerical results, especially in the load rejection process, because disc friction losses, volume losses, and pressure fluctuations in the seal ring (SR) clearance passage are neglected. This paper addresses the issue by considering all of the geometrical details of labyrinth seals when conducting multiscale flow simulations of a high head Francis turbine under a transient load rejection condition using the commercial software code. A comparison of the numerical results that were obtained with the experimental testing data indicates that the calculated values of both torque and mass discharge rate are 8.65% and 5% slightly less than the corresponding values that were obtained from experimental model testing, respectively. The obtained pressure fluctuations of the Francis turbine in the vaneless zone and the draft tube appear to more closely match with the experimental test data when including SR clearance. Moreover, the flow rates through SR clearance passages were very small, but the pressure fluctuations among them were significantly enhanced under the minimal load condition. The numerical model with SR clearance can more accurately reflect the fact that the water thrust on the runner only fluctuates from 800 N to 575 N during the load rejection process, even though the water thrust on the blades varies from −220 N to 1200 N. Therefore, multiscale flow study is of great significance in understanding the effect of clearance flow on the load rejection process in the Francis turbine.