Integrated passage design based on extended free-form deformation and adjoint optimization

Inspired by the three-dimensional design of flow passages in turbomachinery,this study proposes the concept of integrated passage design.The capability of adjoint method for efficient optimization and the flexibility of the parameterization method based on extended free-form defor-mation have been considered to develop a feasible approach to design an integrated passage.This concept was applied to redesign a typical transonic fan,Rotor 67,and the results were analyzed by CFX.It is shown that the passage was adequately adjusted in all three dimensions and reduced the strength of shock wave and wake-induced flow.In particular,the secondary flow was appropriately reorganized and the corner separation was well controlled in the end wall region,leading to signif-icant improvements in adiabatic efficiency and diffusion.

Aerodynamic adjoint optimization of turbomachinery with direct control on blade design parameters

Nowadays,the adjoint method has become a popular approach in the optimization of turbomachinery to further improve its aerodynamic performance.However,design variables in these adjoint optimization applications are generally not direct design parameters of blade(such as wedge angles or maximum thickness),making the geometric variation by adjoint optimization can hardly be re-extracted as the change of each design parameter.By giving considerations to the G1 continuity constraint of adjoint method on its parameterization method,this manuscript shows how to apply a parameterization method in 3D blade design process into adjoint optimization.Nearly all design parameters can therefore be treated as design variables in the adjoint method and then participate in the sensitivity-based optimization.Finally,a fitted Rotor 67 blade is optimized and the adiabatic efficiency is significantly improved by nearly 0.91%.

Study on Adjoint-Based Optimization Method For Multi-Stage Turbomachinery

Adjoint-based optimization method is a hotspot in turbomachinery.First,this paper presents principles of adjoint method from Lagrange multiplier viewpoint.Second,combining a continuous route with thin layer RANS equations,we formulate adjoint equations and anti-physical boundary conditions.Due to the multi-stage environment in turbomachinery,an adjoint interrow mixing method is introduced.Numerical techniques of solving flow equations and adjoint equations are almost the same,and once they are converged respectively,the gradients of an objective function to design variables can be calculated using complex method efficiently.Third,integrating a shape perturbation parameterization and a simple steepest descent method,a frame of adjoint-based aerodynamic shape optimization for multi-stage turbomachinery is constructed.At last,an inverse design of an annular cascade is employed to validate the above approach,and adjoint field of an Aachen 1.5 stage turbine demonstrates the conservation and areflexia of the adjoint interrow mixing method.Then a direct redesign of a 1+1 counter-rotating turbine aiming to increase efficiency and apply constraints to mass flow rate and pressure ratio is taken.

An aerodynamic design and numerical investigation of transonic centrifugal compressor stage

In the present paper,the design of a transonic centrifugal compressor stage with the inlet relative Mach number about 1.3 and detailed flow field investigation by three-dimensional CFD are described.Firstly the CFD program was validated by an experimental case.Then the preliminary aerodynamic design of stage completed through in-house one-dimensional code.Three types of impellers and two sets of stages were computed and analyzed.It can be found that the swept shape of leading edge has prominent influence on the performance and can enlarge the flow range.Similarly,the performance of the stage with swept impeller is better than others.The total pressure ratio and adiabatic efficiency of final geometry achieve 7:1 and 80% respectively.The vane diffuser with same airfoils along span increases attack angle at higher span,and the local flow structure and performance is deteriorated.

An improved prediction model for corner stall in axial compressors with dihedral effect

Corner stall predictions are important and difficult in axial compressors.However,all of the prediction models have proved to be ineffective for advanced compressor blades,which tend to use the combined sweep and dihedral.As for the prediction parameter DL,although it effectively modeled the effects of the adverse pressure gradient and secondary flow,it failed to predict the corner stall of curved blades because the model failed to consider the intersection of the boundary layer at the corner region.In this paper,the shape factor gradientψof the boundary layer at the corner region was investigated by numerically studying specially shaped expansion pipes under different adverse pressure gradients.The improved prediction parameter DJ was presented based on the model of ψ and the circumferential pressure gradient ζ.A comparison of the critical range of the prediction parameters DL and DJ was investigated using the NACA65 cascade database,which was established by a numerical method.Then,the stall criterion was validated according to the experimental results of various test facilities with different blade geometries and experimental conditions.The results show that the improved prediction parameter is able to predict the corner separation/stall flows and is in good agreement with the experimental results for axial compressors with three-dimensional designed blades.

Full blended blade and endwall design of a compressor cascade

In the current state-of-the-art,high-loss flow in the endwall significantly influences compressor performance.Therefore,the control of endwall corner separation in compressor blade rows is important to consider.Based on the previous research of the Blended Blade and End Wall(BBEW)technique,which can significantly reduce corner separation,in combination with a nonaxisymmetric endwall,the full-BBEW technique is proposed in this study to further reduce the separation in endwall region.The principle of the unchanged axial passage area is considered to derive the geometric method for this technique.Three models are further classified based on different geometric characteristics of this technique:the BBEW model,Inclining-Only End Wall(IOEW)model,and full-BBEW model.The most effective design of each model is then found by performing several optimizations at the design point and related numerical investigations over the entire operational conditions.Compared with the prototype,the total pressure loss coefficient decreases by 7%–9%in the optimized full-BBEW at the design point.Moreover,the aerodynamic blockage coefficient over the entire operational range decreases more than the other models,which shows its positive effect for diffusion.This approach has a larger decrease at negative incidence angles where the intersection of the boundary layer plays an important role in corner separation.The analysis shows that the blended blade profile enlarges the dihedral angle and creates a span-wise pressure gradient to move low momentum fluid towards the mainstream.Furthermore,the inclining hub geometry accelerates the accumulated flow in the corner downstream by increasing the pressure gradient.Overall,though losses in the mainstream grow,especially for large incidences,the full-BBEW technique effectively reduces the separation in corners.

Influence of sub boundary layer vortex generator height and attack angle on cross-flows in the hub region of compressors

It has been recently shown that Sub Boundary layer Vortex Generator(SBVG,abbreviated as VG hereafter)can suppress the Cross-Flow(CF),and therefore,can eliminate corner separation and increase aerodynamic loading when installed on the end wall inside middle-load compressor passages.However,when VGs are applied in high-load compressors,it is difficult to achieve ideal results.This is because the definition of the VG attack angle in the presence of CF in existing research is confusing,and the stronger CF in high-load compressors worsens the problem and results in an improper design and optimization range of VG attack angle.Therefore,this paper clarifies the definition of the VG attack angle in the presence of CF and reveals the CF controlling mechanism of VG on a flat plate.The differences in the flow phenomena around a VG both with and without CF are also studied.The numerical results show that a larger height or attack angle of the VG generates a greater CF suppression effect.However,the cross velocity increases when surmounting the primary vortex induced by the VG,except that this enhanced CF is less conspicuous for larger VG heights.Compared to the cases without CF,the VG suffers an additional loss because of the stronger separation and primary vortex loss caused by the CF.