No abstract

This paper presents an anti-erosion design approach of multidisciplinary design optimization (MDO) for turbomachinery to improve the erosion resistance of the blades, and its application to the design of an industrial mixed flow fan is given. The method is based on a concept for turbomachinery anti-erosion design in the aerodynamic design stage by modifying the geometry of the turbomachinery. The MDO approach replaces the traditional time consuming design method through automatic analyses of the aerodynamic performance, stress distribution and erosion characteristics, controlled by the optimization strategy. In the MDO approach, a multi-objective optimization algorithm non-dominated sorting genetic algorithm-II combined with radial basis function meta-model is used to find the compromise between the conflicting demands of high-efficiency and low average erosion rate with constraints on the pressure ratio and the safety factor for the blade; finite element method is used to analyze the static mechanical responses of the blade; a Navier-Stokes solver is used to predict the aerodynamic performance; solid particle paths in a viscous flow are calculated by Lagrangian method, and then the prediction of erosion is performed based on Tabakoff erosion model. Both the aerodynamic and anti-erosion performances of three selected robust optimal solutions on the Pareto front are compared to those of the baseline. The results show that the main reason for the efficiency improvement of the optimized blades is probably the smaller flow separation region and weaker secondary flows. Further comparative analysis between the baseline blade and the compromise blade for the impinging parameters is presented, and the erosion rate of compromise blade can be considerably decreased due to the lower impact velocity, suitable impact angle and fewer impact times in comparison with that of the baseline blade. As a conclusion, it can be drawn that the proposed approach gives a further opportunity for turbomachinery anti-erosion design in consideration of other disciplines, and the methodology presented can be also applied to other turbomachinery and anti-erosion problem by a minor modification.

Among all the elements of a centrifugal fan, the volute is the one that has the lowest flow efficiency. Therefore, improving the performance of the volute is an efficient way to improve the total performance of a centrifugal fan. To contribute a better understanding of the flow structure in the fan volute, the three-dimensional flow in a centrifugal fan volute with a large volute width and rectangular cross-section has been measured in detail by means of five-hole probe at three different flowrates. The time-average swirling and throughflow velocity, static and total pressure distributions on eight cross-sections in the throughflow direction of the volute are presented. The results show the formation and development of the flow in the fan volute of this type, indicate the variation of flow parameters, and discover some peculiar flow phenomena different from the traditional understanding. On the basis of the experimental results, the main hydraulic losses in this kind of fan volute have been preliminarily classified and analysed. The results show that the traditional one-dimensional design method of the volute should be further improved as it is only based on the law of momentum moment conservation and the ideal assumption that the distribution of flow parameters are uniform at the volute inlet.

A multidisciplinary design optimization (MDO) system is established to reduce solid particle erosion of an axial induced draft fan with sweep and lean. The method improves the erosion resistance of the fan blade in the aerodynamic design stage through a change of blade sweep and lean. The multidisciplinary design optimization approach takes the place of the traditional time-consuming design method by automatic calculation of the flow field, stress distribution, dynamic frequencies, and erosion distribution for blade, controlled by an optimization strategy. A multi-objective particle swarm optimization (MOPSO) algorithm combined with radial basis function approximation model is employed for finding a compromise between the conflicting demands of high efficiency and low average erosion rate with constraints on the pressure ratio and structural responses for the blade. The Navier-Stokes solver, finite element method (FEM) is used to predict the aerodynamic performance and mechanical performance of the blade, respectively. Particle paths in a viscous flow are calculated using the Lagrangian method and Tabakoff rebound model. And then Tabakoff erosion model is used to predict erosion of the blade surface. Several representative designs are selected along the Pareto front to verify using computer aided engineering tools. A compromise solution is used to analyze in detail. Compared with the reference design, the optimal design increases the / 0 slightly by 0.53%, while decreases the " avg /" avg0 markedly by 13.7%. The result shows that the optimized blade favors a reduced total pressure due to its forward sweep. The decrease of the " avg / " avg0 is attributed to a reduced impact velocity and impact angle. The analysis of variance technique indicates that the blade lean has a direct impact on performances with respect to efficiency, erosion, and von Mises stress of the blade, and the blade sweep law near hub has an immeasurable influence on blade von Mises stress. As a conclusion, it can be drawn that the proposed approach may open a new opportunity for the design of axial fan to reduce erosion damage of blade taking other disciplines into consideration. Meanwhile, the multidisciplinary design optimization system can be extended to other turbomachinery and erosion-resistant design fields. KeywordsMultidisciplinary design optimization, antierosion design, solid particle erosion, sweep and lean, axial fan Date

To study the effects of micro-groove cross section asymmetry on the flow characteristic and drag reduction efficiency under rotation, numerical simulations of various rotating disks with micro-grooves were performed. Experiments of two representative disks were conducted for comparison and validation. Both numerical results and experimental results show that micro-grooves are effective in drag reduction. The fluid flow is promoted at one micro-groove sidewall and suppressed on the other side. There is an extended low-pressure area between the micro-grooves and the disk clearance, which demonstrates the interaction phenomenon exists, could be discovered. The interaction phenomenon makes the micro-groove fluid suppress the clearance fluid. When the disks rotate, the micro-groove fluids are suppressed, and the extended low-pressure areas are intensified overall. Positive asymmetry coefficient micro-grooves have larger high-pressure areas, and negative asymmetry coefficient micro-grooves have larger low-pressure areas. A higher asymmetry coefficient micro-groove has a greater asymmetrical pressure distribution. In contrast, the extended low-pressure areas are slightly affected by micro-groove geometries. Positive asymmetry coefficient micro-grooves, including zero asymmetry coefficient micro-grooves, have higher drag reduction efficiencies, whereas negative asymmetry coefficient micro-grooves have lower drag reduction efficiencies. The optimal micro-groove asymmetry coefficient is 0.25–0.5 within the rotating Reynolds number limits of 0.703 × 106–1.406 × 106.