Lucheng Ji

Multi-Stage Turbomachinery Blades Optimization Design Using Adjoint Method and Thin Shear-Layer N-S Equations

Traditionally, 3D aerodynamic shape design with the aid of optimization algorithm in an analysis mode has provided a rational and direct search through design space, but it is usually too time-consuming. Further improvement to reduce design cycle is probably a necessary concern in turbomachinery community. Due to less computational cost, adjoint method has received considerable attention in recent years. This paper focuses on continuous adjoint method, and couples with thin shear-layer N-S equations to formulate an efficient sensitivity analysis model for multi-stage turbomachinery blades in the specified objective function. This model includes adjoint equations/boundary conditions, and the sensitivity of objective function to design variable vector. Integrating a 3D blade perturbation parameterization and the simple steepest decent method, a frame of a gradient-based aerodynamic shape design system is constructed. Numerical implementation to solve flow equations and adjoint equations is very similar, and once they are converged respectively, the sensitivity can be calculated by complex method and mesh perturbation efficiently. Thus, a fast Automatic-CFD-Design tool is developed, including three sub-solvers to solve flow equations, adjoint equations and calculate sensitivity respectively. Flow surface design of a 1-1/2 compressor stage in the specified target pressure distribution is used to validate the present approach. Flow field design of NASA transonic compressor stage 35 aiming to increase efficiency and remain mass flow rate and pressure ratio unchanged is taken.© 2012 ASME

Numerical Studies on Improving Performance of Rotor-67 by Blended Blade and EndWall Technique

The paper describes an advanced blading concept for highly loaded turbomachinery, named as Blended Blade and EndWall (BBEW). It implies the following three separate aspects or any of their combinations, i.e. increasing the dihedral between blade surface and endwall as much as possible, increasing the minimum curvature radius of curved transition surface that connects the blade with the endwall, and decreasing the streamwise gradient of the dihedral as the dihedral reduces streamwise. To the knowledge of the authors this is the first approach reported in the open literature that try to control corner separations and horse-shoe vortex (HSV) systematically under the guidance of the Rules of Dihedral (RD). In this paper, BBEW is applied to NASA rotor 67 which is featured by hub corner separation at the suction side and intensive HSV originating from blade leading edge at the hub. Two successive BBEW modifications are made to promote the performance of rotor 67. First, only a curved transition surface is designed to cover the hub corner at the suction side. Emphasis is paid on the streamwise distribution of the minimum curvature radius. Then, the second curved transition surface is added at the leading edge in near hub part. The nearby streamwise gradient of the dihedral is changed from infinity to a finite. Numerical tests showed that the implementation of BBEW had not only nearly eliminated the hub corner separation, but also weakened the leading edge HSV. Performance improvements are observed throughout its operation range. The work presented makes a contribution to a fully 3-D blading methodology for higher aerodynamic loading, engine efficiency and specific thrust.Copyright

Review and Understanding on Sweep in Axial Compressor Design

As a means of improving axial compressor performance, sweep technique has been investigated for over half a century and gained wide uses, in the past one decade. However, there is still diverse controversy about the roles of sweep in axial compressor design. In this paper, historical remarks about the sweep are presented firstly. Then, an understanding about the role of sweep is put forward. That is, the sweep is a degree of freedom (DOF) of blade design that emphasizes on matching the aerodynamic loading of every blade element along the whole span within the full operation range. The present understanding about the role of sweep may lead it a more sophisticated use.Copyright

Further Development of a Riemann-solver Free Space-time Discontinuous Galerkin Method for Compressible Magnetohydrodynamics (MHD) Equations

This paper reports our recent development of our Riemann-solver free space-time discontinuous Galerkin method to solve the ideal compressible magnetohydrodynamics (MHD) equations. The preliminary results we have for 1-D 7 × 7 and 2-D 8 × 8 MHD equations show that the method is able to capture the complex MHD waves correctly without the need of any type of Riemann solvers or other flux functions, which makes our method very promising in solving systems where accurate and reliable Riemann solvers are difficult to design.

Analysis of Technical Challenges in Vaneless Counter-Rotating Turbomachinery

Research and development of vaneless counter-rotating turbomachinery (VCRT) is briefly reviewed. Then basic technical challenges on inflow angle and off-design operation are analyzed regardless of extrinsic differences among any kinds of VCRT (either compressor or turbine or lift fan, either highly or moderately loaded). A somewhat new approach based on velocity triangle analysis played the most important role in obtaining useful results. It is shown that the range of relative inflow angle of the second rotor is narrowed by counter-rotation. And as compared with conventional turbomachinery, varying back-pressure and varying rotation speed off-design operation of VCRT are more complicated. For some rotation speed ratios and flow coefficients, VCRT leads to better operation of varying back pressure type than conventional one, whereas some not. In varying rotation speed operation, VCRT needs variable rotor to get a comparable performance. Counter-measures to overcome these challenges are also given. These analyses will be directly used to judge the applicability of VCRT and determine basic rules and ranges in selecting design parameters of VCRT.Copyright

Study on aerodynamic optimal super/transonic turbine cascade and its geometry characteristics

The shock waves are important phenomena in transonic turbines, which cause lots of negative effects on the aerodynamic performance. Much of attention had been paid on reducing the strength of the shock waves via modifying turbine cascade geometry, and it is highly preferred to build experiences on the relationship between the cascade aerodynamic performance and the geometric parameters. The paper presents a numerical study on the aerodynamic optimal transonic turbine cascade and its geometry characteristics. Three typical Russia transonic turbine cascades with different design conditions are selected and optimized using adjoint method at three different back pressures, respectively. Thus, the best geometry parameters for optimum aerodynamic performance can be found. Then the key geometry parameters of optimized cascades are extracted and compared with the original ones. Results show that even the best designs by hands could be less efficient than ones by computer-aided optimizations. Some experiences on how to set the key geometry parameters for a best performance are obtained. The reduced shock profiling is applied to the thermal turbomachinery and machine dynamics transonic turbine by using the adjoint method. The performance of the thermal turbomachinery and machine dynamics transonic turbine was increased significantly.

Research on interior ballistic mechanics of electromagnetic railgun

Low efficiency of energy utilization is one of the most important bottlenecks for the electromagnetic railgun to go into application. While any improvement in emission efficiency presents amplifying effect in saving the overall energy, so it is very necessary to reduce aerodynamic losses generated during the projectile emission. In this paper, the view of interior ballistic aerodynamic losses in the emission of electromagnetic railgun is introduced. Through mathematical analysis and dynamic mesh CFD (computational fluid dynamics) simulations, explore the interior ballistic law and optimize aerodynamic shape of the projectile. The interior ballistic researches show that improving the electromagnetic force and the aerodynamic drag ratio can improve the emission efficiency of electromagnetic railgun, increasing the clearance between projectile and barrel can reduce the aerodynamic losses. For the aerodynamic shape, increasing the slenderness ratio, reducing the cone angle and so on can reduce aerodynamic losses. Whats more, through the researches, we found that the aerodynamic optimizations are more valuable for large high-velocity projectile.

Study of Hot Streak Effects in a Counter-Rotating Turbine

Based on its convection nature, some influences of the hot streak on a 1+1 (with inter-blade vane) counter-rotating turbine are studied by using a three-dimensional (3D) unsteady Euler solver. Emphasis is laid on the hot streak effect to the blade heat load and the clocking effects between hot streak and blade rows. One temperature distortion magnitude, two spanwise and four tangential positions, four clocking locations between vanes of first and second stage are examined. Results show that the effect of the hot streak on a counter-rotating turbine is nearly the same as a conventional turbine. However, clocking between the hot streak and the vane of the high pressure turbine (HPT) exerts significant influences on the heat load of the whole HPT stage. Also, clocking between the HPT vane and the vane of the low pressure turbine (LPT) affects the heat load of the LPT greatly. These effects cannot be captured with the steady flow assumption. So time accurate simulation about the hot streak/blade interaction must be used as a basis for the turbine design and optimization.Copyright

Adjoint Optimization of Multistage Axial Compressor Blades with Static Pressure Constraint at Blade Row Interface

Abstract Adjoint method is an important tool for design refinement of multistage compressors. However, the radial static pressure distribution deviates during the optimization procedure and deteriorates the overall performance, producing final designs that are not well suited for realistic engineering applications. In previous development work on multistage turbomachinery blade optimization using adjoint method and thin shear-layer N-S equations, the entropy production is selected as the objective function with given mass flow rate and total pressure ratio as imposed constraints. The radial static pressure distribution at the interfaces between rows is introduced as a new constraint in the present paper. The approach is applied to the redesign of a five-stage axial compressor, and the results obtained with and without the constraint on the radial static pressure distribution at the interfaces between rows are discussed in detail. The results show that the redesign without the radial static pressure distribution constraint (RSPDC) gives an optimal solution that shows deviations on radial static pressure distribution, especially at rotor exit tip region. On the other hand, the redesign with the RSPDC successfully keeps the radial static pressure distribution at the interfaces between rows and make sure that the optimization results are applicable in a practical engineering design.

Shape Optimization of Axial Compressor Blades Using Adjoint Method With Emphasis on Thickness Distribution

Shape parameterization plays an important role in aerodynamic optimization design of axial compressor blades. Blade thickness is one of the most important parameters in blade design, which has strong influence on compressor aerodynamic performance. However, the previous adjoint-based optimization designs using the Hicks-Henne functions only parameterized the perturbations to the tangential coordinates of points on suction surface or meanline, and kept the tangential thickness of the blade constant during the optimization process. In previous development work of turbomachinery blade optimization using adjoint method and thin shear-layer N-S equations, a new shape parameterization is introduced, which uses Hicks-Henne functions to parameterize the perturbations to both the tangential coordinates of mesh points on suction blade surface and the tangential thickness of the blade. This new approach is applied to the redesign of NASA rotor 67 and the results obtained with and without the blade tangential thickness parameterization are discussed in detail. The results show the redesign with and without the blade tangential thickness parameterization can both improve the aerodynamic performance of the axial compressor. However, the redesign with the blade tangential thickness parameterization can produce a consistently better performance than that without it.Copyright