Three-dimensional Inverse Design Method Research Articles

Design analysis and optimisation of an integrated motor pump-jet thruster with improved resistance to cavitation

ABSTRACT In order to meet the basic design requirements for high critical speed met, and anti-cavitation performance enhanced of Integrated Motor Pump-Jet (IMP) thrusters, a three-dimensional model of the IMP thruster using the blade parameter three-dimensional (3D) inverse design method was developed. The model utilises the shear stress transport (SST) turbulence model and the Zwart–Gerber–Belamri (Z-G-B) cavitation model. Then, based on the non-dominated ranking genetic algorithm and multi-objective parameter seeking theory to improve the IMP thruster's cavitation improvement optimization design. After optimisation, the hydrodynamic performance and anti-cavitation performance of the rotor blades were slightly improved. In order to further carry out the design of anti-cavitation performance, the oblique flow is introduced to further analyse according to the influence mechanism. The main focus was on the IMP thruster's excitation force, pulsation pressure and velocity distribution, the oblique flow angle had less impact than the cavitation number in the oblique flow field.

Multi-Objective Optimization of a High Specific Speed Centrifugal Volute Pump Using Three-Dimensional Inverse Design Coupled With Computational Fluid Dynamics Simulations

AbstractThis paper presents three different multiobjective optimization strategies for a high specific speed centrifugal volute pump design. The objectives of the optimization consist of maximizing the efficiency and minimizing the cavitation while maintaining the Euler head. The first two optimization strategies use a three-dimensional (3D) inverse design method to parametrize the blade geometry. Both meridional shape and 3D blade geometry are changed during the optimization. In the first approach, design of experiment (DOE) method is used and the pump efficiency is obtained from computational fluid dynamics (CFD) simulations, while cavitation is evaluated by using minimum pressure on blade surface predicted by 3D inverse design method. The design matrix is then used to create a surrogate model where optimization is run to find the best tradeoff between cavitation and efficiency. This optimized geometry is manufactured and tested and is found to be 3.9% more efficient than the baseline with reduced cavitation at high flow. In the second approach, only the 3D inverse design method output is used to compute the efficiency and cavitation parameters and this leads to considerable reduction to the computational time. The resulting optimized geometry is found to be similar to the computationally more expensive solution based on 3D CFD results. In order to compare the inverse design based optimization to the conventional optimization, an equivalent optimization is carried out by parametrizing the blade angle and meridional shape.

Three-Dimensional Inverse Design Method for Hydraulic Machinery

Hydraulic machinery with high performance is of great significance for energy saving. Its design is a very challenging job for designers, and the inverse design method is a competitive way to do the job. The three-dimensional inverse design method and its applications to hydraulic machinery are herein reviewed. The flow is calculated based on potential flow theory, and the blade shape is calculated based on flow-tangency condition according to the calculated flow velocity. We also explain flow control theory by suppression of secondary flow and cavitation based on careful tailoring of the blade loading distribution and stacking condition in the inverse design of hydraulic machinery. Suggestions about the main challenge and future prospective of the inverse design method are given.

The Influence of Blade Tip Loading Distribution on the Performance of a High Loading Centrifugal Impeller

It has been proved that different blade loading distributions between tip and hub has a significant effect on centrifugal impeller performance, but the effect of loading difference at different location along the stream has not been fully understood. In this paper, several blades were modelled by a three-dimensional inverse design method, in which the impellers are defined by the blade loading distribution at its tip and hub and the flows are computed numerically by a commercial CFD code. Firstly, two impellers were modelled using the same distribution at the hub but giving different distributions at tip. The results show that the impeller with a smoother tip loading distribution performs better. At design flow rate, the total pressure ratio is found to be 1.8% higher and the efficiency rises 1.36% as well. Then a further research about the effect of increasing tip load at different parts along the flow path was carried out. Further analysis indicates that adding the load at the fore part of tip could increase the efficiency at design flow rate and brings more uniform impeller exit flow. However, the surge margin was narrowed by such change. Besides, adding the vur at the aft part of tip will promote the pressure ratio, with no adverse effect on the stable operation range.

Optimization of a Centrifugal Impeller with the Constraint on Efficiency at the Stall Point

An optimization strategy is presented concerning the aerodynamic performance of an impeller at the design point with a constraint of efficiency at the stall point, on the basis of the combination of three-dimensional inverse design method and the response surface methodology (RSM). A specific inlet angular momentum is given in the prescribed blade loading to facilitate the change of the blade inlet angle at either the hub or shroud of the impeller. Three variables, the inlet angular momentums at both the hub and shroud as well as a coefficient relation with blade loading, were chosen as the optimization variables after a sensitivity analysis, which is conducted by means of the orthogonal design experiment. The candidate impellers were generated by different angular momentum distributions determined by the Box-Behnken design, and the performances of corresponding compressors were simulated. The response surface models of the performances of the compressors were obtained at the design and stall points. Thus the optimal impeller was obtained and the compressor’s performance at the design flow rate could be predicted under the constraint of a specified efficiency at the stall flow rate. A comparison between the computational results of the original and optimized impeller indicates that a considerable improvement of the efficiency of the compressor over the whole working range is obtained, which confirms the validity of the optimization strategy.

Redesign of a Compressor Stage for a High-Performance Electric Supercharger in a Heavily Downsized Engine

Engine downsizing is a modern solution for the reduction of CO2 emissions from internal combustion engines. This technology has been gaining increasing attention from industry. In order to enable a downsized engine to operate properly at low speed conditions, it is essential to have a compressor stage with very good surge margin. The ported shroud, also known as the casing treatment, is a conventional way used in turbochargers to widen the working range. However, the ported shroud works effectively only at pressure ratios higher than 3:1. At lower pressure ratio, its advantages for surge margin enhancements are very limited. The variable inlet guide vanes are also a solution to this problem. By adjusting the setting angles of variable inlet guide vanes, it is possible to shift the compressor map toward the smaller flow rates. However, this would also undermine the stage efficiency, require extra space for installing the inlet guide vanes, and add costs. The best solution is therefore to improve the design of impeller blade itself to attain high aerodynamic performances and wide operating ranges. This paper reports a recent study of using inverse design method for the redesign of a centrifugal compressor stage used in an electric supercharger, including the impeller blade and volute. The main requirements were to substantially increase the stable operating range of the compressor in order to meet the demands of the downsized engine. The three-dimensional (3D) inverse design method was used to optimize the impeller geometry and achieve higher efficiency and stable operating range. The predicted performance map shows great advantages when compared with the existing design. To validate the computational fluid dynamics (CFD) results, this new compressor stage has also been prototyped and tested. It will be shown that the CFD predictions have very good agreement with experiments and the redesigned compressor stage has improved the pressure ratio, aerodynamic efficiency, choke, and surge margins considerably.

Multi-objective optimization of a mixed-flow pump impeller using modified NSGA-II algorithm

In order to maintain a uniform distribution of pareto-front solutions, a modified NSGA-II algorithm coupled with a dynamic crowding distance (DCD) method is proposed for the multi-objective optimization of a mixed-flow pump impeller. With the pump meridional section fixed, ten variables along the shroud and hub are selected to control the blade load by using a three-dimensional inverse design method. Hydraulic efficiency, along with impeller head, is applied as an optimization objective; and a radial basis neural network (RBNN) is adopted to approximate the objective function with 82 training samples. Local sensitivity analysis shows that decision variables have different impacts on the optimization objectives. Instead of randomly selecting one solution to implement, a technique for ordering preferences by similarity to ideal solution (TOPSIS) is introduced to select the best compromise solution (BCS) from pareto-front sets. The proposed method is applied to optimize the baseline model, i.e. a mixed- flow waterjet pump whose specific speed is 508 min-1·m3s-1·m. The performance of the waterjet pump was experimentally tested. Compared with the baseline model, the optimized impeller has a better hydraulic efficiency of 92% as well as a higher impeller head at the design operation point. Furthermore, the off-design performance is improved with a wider high- efficiency operation range. After optimization, velocity gradients on the suction surface are smoother and flow separations are eliminated at the blade inlet part. Thus, the authors believe the proposed method is helpful for optimizing the mixed-flow pumps.

Parametric design of a Francis turbine runner by means of a three-dimensional inverse design method

The present paper describes the parametric design of a Francis turbine runner. The runner geometry is parameterized by means of a 3D inverse design method, while CFD analyses were performed to assess the hydrodymanic and suction performance of different design configurations that were investigated. An initial runner design was first generated and used as baseline for parametric study. The effects of several design parameter, namely stacking condition and blade loading was then investigated in order to determine their effect on the suction performance. The use of blade parameterization using the inverse method lead to a major advantage for design of Francis turbine runners, as the three-dimensional blade shape is describe by parameters that closely related to the flow field namely blade loading and stacking condition that have a direct impact on the hydrodynamics of the flow field. On the basis of this study, an optimum configuration was designed which results in a cavitation free flow in the runner, while maintaining a high level of hydraulic efficiency. The paper highlights design guidelines for application of inverse design method to Francis turbine runners. The design guidelines have a general validity and can be used for similar design applications since they are based on flow field analyses and on hydrodynamic design parameters.

On the Coupling of Inverse Design and Optimization Techniques for the Multiobjective, Multipoint Design of Turbomachinery Blades

Automatic optimization techniques have been used in recent years for the aerodynamic and mechanical design of turbomachine components. Despite the many advantages, their use is usually limited to simple applications in industrial practice, because of their high computational cost. In this paper, an optimization strategy is presented, which enables the three-dimensional multipoint, multiobjective aerodynamic optimization of turbomachinery blades in a time frame compatible with industrial standards. The design strategy is based on the coupling of three-dimensional inverse design, response surface method, multiobjective evolutionary algorithms, and computational fluid dynamics analyses. The blade parametrization is performed by means of a three-dimensional inverse design method, where aerodynamic parameters, such as the blade loading, are used to describe the blade shape. Such a parametrization allows for a direct control of the aerodynamic flow field and performance, leading to a major advantage in the optimization process. The design method was applied to the redesign of a centrifugal and of an axial compressor stage. The two examples confirmed the validity of the design strategy to perform the three-dimensional optimization of turbomachine components, accounting for both design and off-design performance, in a time-efficient manner. The coupling of response functions and inverse design parametrization also allowed for an easy sensitivity analysis of the impact of the design parameters on the performance ones, contributing to the development of design guidelines that can be exploited for similar design applications.

1706 半開放形プロペラファンの三次元空力設計(S19-1 流体機械に関連した流動現象とその解析・計測(1)ファン内流れの計測と解析,21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

A three-dimensional aerodynamic design method for half-ducted propeller fan has been presented. The half-ducted propeller fan has internal and external flow feature. It is important to take into account non-uniform meridional flow distributions around it. The present design method consists of two parts: a three-dimensional inverse design of fan rotor blade and an axisymmetric viscous flow calculation on the meridional plane. Continuing the process between the blade design using the three-dimensional inverse design method and the evaluation of the viscous flow fields around the rotor using the axisymmetric viscous flow calculation, the blade shape matching the flow fields around the rotor is converged. It is found that the present design method is useful to the half-ducted propeller fan design tool.

1635 斜流ポンプの多目的最適化設計 : 第1報 設計パラメータの感度解析(J12-2 流体機械に関連した流体解析と数値最適化技術(2),J12 流体機械に関連した流体解析と数値最適化技術)

A sensitivity analysis of mixed-flow impeller's design parameters was performed in the first stage of optimization design of mixed-flow pumps that have a performance trade-off. High efficiency, non-stall, and low shut-off power were set as objective functions. This study was done by combining the three-dimensional inverse design method and CFD, some design parameters of impeller were founded to have trade-off problem for performance.

Hydrodynamic Design of Pump Diffuser Using Inverse Design Method and CFD

A new approach to optimizing a pump diffuser is presented, based on a three-dimensional inverse design method and a Computational Fluid Dynamics (CFD) technique. The blade shape of the diffuser was designed for a specified distribution of circulation and a given meridional geometry at a low specific speed of 0.109 (non-dimensional) or 280 (m3/min, m, rpm). To optimize the three-dimensional pressure fields and the secondary flow behavior inside the flow passage, the diffuser blade was more fore-loaded at the hub side as compared with the casing side. Numerical calculations, using a stage version of Dawes three-dimensional Navier-Stokes code, showed that such a loading distribution can suppress flow separation at the corner region between the hub and the blade suction surface, which was commonly observed with conventional designs having a compact bowl size (small outer diameter). The improvements in stage efficiency were confirmed experimentally over the corresponding conventional pump stage. The application of multi-color oil-film flow visualization confirmed that the large area of the corner separation was completely eliminated in the inverse design diffuser.

Three-Dimensional Automatic Optimization Method for Turbomachinery Blade Design

In deriving automatic numerical optimization algorithms for aerodynamic applications, it is quite important to choose a suitable cost function and a suitable set of design parameters. The unknown airfoil/blade profiles are usually chosen to be the design parameters. However, there are certain advantages in using the pressure/velocity distribution as the design variable in some applications; the optimized distribution can be used in a three-dimensional inverse design method to generate the actual profile shape. In this paper this approach will be addressed. Two methods are used to parameterize the circulation distribution for compressor blades. The Dawes code is used to calculate the viscous effect. An automatic optimization algorithm is developed, and two objective functions defined by the entropy loss or the aerodynamic blockage are examined.

Inverse Design and CFD Investigation of Blood Pump Impeller

In this paper, a three-dimensional inverse design method using mean swirl specification is applied to the design of centrifugal blood pump impeller blades. CFD investigation of the passage flows is carried out to analyze the flow field and pressure generated across the blade. The results show that the possibility of blood cells' damage may not be increased when the pressure developed is increased. This technique can provide designers valuable insight on the development of efficient blood pump with reduced risk of blood traumatization.

On the role of three-dimensional inverse design methods in turbomachinery shape optimization

The application of a three-dimensional (3D) inverse design method in which the blade geometry is computed for a specified distribution of circulation to the design of turbomachinery blades is explored by using two examples. In the first instance the method is applied to the design of radial and mixed flow impellers to suppress secondary flows. Based on our understanding of the fluid dynamics of the flow in the impeller, simple guidelines are developed for input specification of the inverse method in order to systematically design impellers with suppressed secondary flows and a more uniform exit flow field. In the second example the method is applied to the design of a vaned diffuser. Again based on the understanding of the detailed flow field in the diffuser obtained by using 3D viscous calculations and oil flow visualizations, simple design guidelines are developed for input specification to the inverse method in order to suppress corner separation. In both cases the guidelines are verified numerically and in the case of the diffuser further experimental validation is presented.

On the Simultaneous Design of Blade and Duct Geometry of Marine Ducted Propulsors

In ducted propulsor design for marine vessels, due to the strong interaction between the duct and the propeller blades, it is very important to design the duct and the blade geometry simultaneously. Here, a three-dimensional inverse design method is presented to take this into consideration. The method is based on three-dimensional potential flow; however, the effect of the inlet shear flow and the resulting rotational flow is also modeled via the Clebsch formulation. The duct profile is designed to achieve a target velocity distribution while the blade geometry is computed to attain a desired mass-flow rate and a certain circulation distribution. The method is applied to the design of three generic ducted propulsors with a 7-bladed contrarotating configuration.

On the Design Criteria for Suppression of Secondary Flows in Centrifugal and Mixed Flow Impellers

In this paper, for the first time, a set of guidelines is presented for the systematic design of mixed flow and centrifugal compressors and pumps with suppressed secondary flows and a uniform exit flow field. The paper describes the shape of the optimum pressure distribution for the suppression of secondary flows in the impeller with reference to classical secondary flow theory. The feasibility of achieving this pressure distribution is then demonstrated by deriving guidelines for the design specifications of a three-dimensional inverse design method, in which the blades are designed subject to a specified circulation distribution or 2πrVθ. The guidelines will define the optimum choice of the blade loading or ∂rVθ/∂m and the stacking condition for the blades. These guidelines are then used in the design of three different low specific speed centrifugal pump impellers and a high specific speed industrial centrifugal compressor impellers. The flows through all the designed impellers are computed numerically by a three-dimensional viscous code and the resulting flow field is compared to that obtained in the corresponding conventional impeller. The results show consistent suppression of secondary flows in all cases. The design guidelines are validated experimentally by comparing the performance of the inverse designed centrifugal compressor impeller with the corresponding conventional impeller. The overall performance of the stage with the inverse designed impeller with suppressed secondary flows was found to be 5 percent higher than the conventional impeller at the peak efficiency point. Exit flow traverse results at the impeller exit indicate a more uniform exit flow than that measured at the exit from the conventional impeller.

Suppression of Secondary Flows in a Mixed-Flow Pump Impeller by Application of Three-Dimensional Inverse Design Method: Part 1—Design and Numerical Validation

This paper describes the design of the blade geometry of a medium specific speed mixed flow pump impeller by using a three-dimensional inverse design method in which the blade circulation (or rVθ) is specified. The design objective is the reduction of impeller exit flow nonuniformity by reducing the secondary flows on the blade suction surface. The paper describes in detail the aerodynamic criteria used for the suppression of secondary flows with reference to the loading distribution and blade stacking condition used in the design. The flow through the designed impeller is computed by Dawes’ viscous code, which indicates that the secondary flows are well suppressed on the suction surface. Comparison between the predicted exit flow field of the inverse designed impeller and a corresponding conventional impeller indicates that the suppression of secondary flows has resulted in substantial improvement in the exit flow field. Experimental comparison of the flow fields inside and at exit from the conventional and the inverse designed impeller is made in Part 2 of the paper.

Suppression of Secondary Flows in a Mixed-Flow Pump Impeller by Application of Three-Dimensional Inverse Design Method: Part 2—Experimental Validation

In Part 1 of this paper, a mixed-flow pump impeller was designed by a fully three-dimensional inverse design method, aimed at suppressing the secondary flows on the blade suction surface. In this part, the internal flow fields of the impeller are investigated experimentally, using flow visualization and phase-locked measurements of the impeller exit flow, in order to validate the effects of secondary flow suppression. The flow fields are compared with those of a conventional impeller, and it is confirmed that the secondary flows on the blade suction surface are well suppressed and the uniformity of the exit flow fields is improved substantially, in both circumferential and spanwise directions. The effects of tip clearance and the number of blades for the inverse designed impeller are also investigated experimentally and numerically.

Inverse Design of Centrifugal Compressor Vaned Diffusers in Inlet Shear Flows

A three-dimensional inverse design method in which the blade (or vane) geometry is designed for specified distributions of circulation and blade thickness is applied to the design of centrifugal compressor vaned diffusers. Two generic diffusers are designed, one with uniform inlet flow (equivalent to a conventional design) and the other with a sheared inlet flow. The inlet shear flow effects are modeled in the design method by using the so-called “Secondary Flow Approximation” in which the Bernoulli surfaces are convected by the tangentially mean inviscid flow field. The difference between the vane geometry of the uniform inlet flow and nonuniform inlet flow diffusers is found to be most significant from 50 percent chord to the trailing edge region. The flows through both diffusers are computed by using Denton’s three-dimensional inviscid Euler solver and Dawes’ three-dimensional Navier–Stokes solver under sheared in-flow conditions. The predictions indicate improved pressure recovery and internal flow field for the diffuser designed for shear inlet flow conditions.