Design optimization workflow and performance analysis for contoured endwalls of axial turbines (original) (raw)
Related papers
Volume 2C: Turbomachinery, 2014
This paper presents a novel optimisation methodology based on both Adjoint sensitivity analysis and trust-based dynamic response surface modelling to improve performance of a modern turbine of a large civil aero-engine in the presence of high-fidelity geometry configurations. The system has been applied to the non-axisymmetric hub and tip endwall optimisation of a high-pressure turbine stage making use of multi-row 3D simulations, parametric modelling and rapid meshing of real geometry features such as rim seals and modelling of film cooling flows. It has been shown in previous papers that improvements gained using simplified models of the stage are lost when applying the high-fidelity geometry configuration. New results presented in this paper indicate that controlling the purge flow that exits the disc space through the rim seal at the hub of the main annulus is more significant than the reduction of secondary flows in the main passage. For a given rim sealing mass flow rate and whirl velocity, the non-axisymmetric endwalls are optimised such that the detrimental impact of the sealing flow on the turbine performance is reduced, and hence the stage efficiency is significantly increased. The traditional optimisation approaches based on evolutionary methods or even sequential modifications for defining the endwalls shape are computationally demanding. Since, turbomachinery industry continuously strive to reduce the design cycle time, in particular when high fidelity 3D CFD is used, the main body of this paper outlines the novel methods developed to produce a practical design in a very aggressively short design cycle time.
Optimization of the non-axisymmetric stator casing of a 1.5 stage axial turbine
International Journal of Mechanical Sciences
The interaction of secondary flows with the main passage flow in turbomachines results in entropy generation and in aerodynamic loss. This loss source is most relevant to low aspect ratio blades. One approach for reducing this flow energy loss is by end-wall contouring. However, limited work has been reported on using non-axisymmetric end-walls at the stator casing and on its interaction with the tip leakage flow. In this paper, a non-axisymmetric end-wall design method for the stator casing is implemented through a novel surface definition, towards mitigating secondary flow losses. This design is tested on a three-dimensional axial turbine RANS model built in OpenFOAM Extend 3.2, with − SST turbulence closure. Flow analysis confirm the foundations of the new surface definition approach, which is implemented using Alstom Process and Optimization Workbench (APOW) software. Computer-based optimization of the surface topology is demonstrated towards automating the design process of axial turbines in an industrial design workflow. The design is optimized using the total pressure loss across the first stator and across the full stage, as the target function. Numerical predictions of the 1.5 stage axial turbine show the positive impact of the optimized casing design on the efficiency that increases by 0.69% against the benchmark axisymmetric stage from RTWH Aachen, which is validated against experiment. The new non-axisymmetric casing is also beneficial at off-design condition. The effective mitigation of the secondary flows is predicted to give a 0.73% efficiency gain off-design.
IRJET- Axial Flow Turbine Aerodynamic Shape Design optimization
IRJET, 2020
This paper presents an axial turbine blade metamodeling (surrogate modeling) process performing the axial turbine blade aerodynamic shape design optimization, based on the axial turbine design parameters. This modeling technique is applied on the rotor blade of the axial flow turbine stage, working through the small turbojet engine JETCAT P 200. This metamodel consists of 140 turbine stage CFD models, generated by varying the inlet and exit meanline airfoil cone angles of the rotor blade within certain range using the integrated random sampling function in the commercial program MATLAB. The flow field of these models is solved numerically by the commercial CFD code ANSYS CFX. The objective of these optimization process is to study the effect of blade profile shape change on the different aerothermodynamic performance parameters of the axial turbine stage. A special code is designed on MATLAB to collect the resultant data of great concern from the pre-solved CFD models. The CFD generated data is interpolated and presented in graphs using the integrated curve fitting APPS in MATLAB to study the relationship between the turbine blade profile change and the axial turbine stage working conditions, which is the Surrogate Modeling. The presented parameters are the total-total isentropic efficiency, exit stage total pressure, turbine work, engine thrust, mass flow rate through the turbine stage. A multi objective optimization using the Surrogate Model generated data to determine the optimum working point according to the requirements of the present case study. 2 Introduction At the end of the design cycle, it becomes essential to optimize the design according to the requirements of the working application. In the field of axial flow turbine shape design optimization, there is no direct relationship between the turbine shape design parameters and the flow working conditions (cannot be represented by a direct equation). The mass, momentum and energy transfer of the flow through the axial flow turbine are governed by a non-linear 2 nd order partial differential equations (could'not be solved analytically), so, the flow field around the axial turbine blades needs to be evaluated numerically using the CFD techniques. In the present case, there is no direct relationship between i.e. turbine total-total efficiency and the blade profile shape parameters, so, using the conventional optimization algorithms like Genetic Algorithm (GA) are so difficult to be applied. The optimization process using the conventional GA needs designing of special codes of high-level language which is out of scope of most of the turbomachinery designers and takes much time to be achieved. Surrogate model or metamodel will be efficient to be used here, which is called the Aerodynamic design optimization (ADO). The first step of performing this technique is to design a CFD model representing the studied axial turbine stage using its dimensions and working conditions. The flow parameters (objective) are obtained numerically by solving the turbine stage flow-field over the real case working domain using the commercial CFD code ANSYS CFX. After validating the results of the designed CFD model, it becomes the High-Fidelity Model. The domain of the experiment should be designed with a fair number of CFD models, and the response surface is generated for the flow parameters of great concern separately. The response surface is a three axes graph, in which, the independent parameters are represented on the x and y axes, while the z axis represents the resultant data from the CFD code for the objective parameter. The response surface becomes the direct mathematical relationship between the independent variable and flow parameters. The mathematical equation of the response surface is now easy to be obtained using the modern programs like i.e. MATLAB or EXCEL. A check step here is essential by solving more number of high-fidelity models and comparing its results with those are predicted using the generated response surface. A new phase of the optimization process is ready to be achieved, the role of the high-fidelity model (the CFD work) is finished. The response surface becomes the main model to predict the needed turbine performance parameters data for any proposed model over the designed domain of experiment and for any further optimization work [1]. The Aerodynamic Design Optimization is recently increased due to the increasing demands for optimizing complicated geometries like studying the different turbomachinery blade profiles, achieving improved operating conditions, and satisfying several design and market requirements. Since the aerodynamic design works mainly depend on numerical simulation computer codes, the use of ADO is now strongly preferred because of the increasing capabilities of modern super computers.
Nonaxisymmetric Turbine End Wall Design: Part I— Three-Dimensional Linear Design System
Journal of Turbomachinery, 2000
A linear design system, already in use for the forward and inverse design of threedimensional turbine aerofoils, has been extended for the design of their end walls. This paper shows how this method has been applied to the design of a nonaxisymmetric end wall for a turbine rotor blade in linear cascade. The calculations show that nonaxisymmetric end wall profiling is a powerful tool for reducing secondary flows, in particular the secondary kinetic energy and exit angle deviations. Simple end wall profiling is shown to be at least as beneficial aerodynamically as the now standard techniques of differentially skewing aerofoil sections up the span, and (compound) leaning of the aerofoil. A design is presented that combines a number of end wall features aimed at reducing secondary loss and flow deviation. The experimental study of this geometry, aimed at validating the design method, is the subject of the second part of this paper. The effects of end wall perturbations on the flow field are calculated using a three-dimensional pressure correction based Reynolds-averaged Navier-Stokes CFD code. These calculations are normally performed overnight on a cluster of work stations. The design system then calculates the relationships between perturbations in the end wall and resulting changes in the flow field. With these available, linear superposition theory is used to enable the designer to investigate quickly the effect on the flow field of many combinations of end wall shapes (a matter of minutes for each shape).
A Novel Nonaxisymmetric Endwall Contouring for Turbine Cascade Using Automated Optimization
A novel nonaxisymmtric endwall contouring is presented to suppress the corner separation and to produce a more uniform exit flow angles. Firstly, a design methodology of automated optimization based on baseline is put forward. Hereafter, with respect to the contoured endwall and baseline, numerical simulations are conducted in an effort to gain further understanding of the effects of endwall contouring. The results demonstrate that with the addition of nonaxisymmetric endwall, the corner separation is enormously suppressed owing to the redistribution of the blade loading in the blade passage, furthermore, the total loss coefficient is decreased by 10% in the 128% Cax plane, and the underturning of the flow is reduced to a high degree, which clarifies the mechanisms of reduction in the secondary flow losses.
Aerodynamic Shape Optimization of Axial Turbines in Three Dimensional Flow
2012
Aerodynamic shape optimization of axial gas turbines in three dimensional flow is addressed. An effective and practical shape parameterization strategy for turbine stages is introduced to minimize the adverse effects of three-dimensional flow features on the turbine performance. The optimization method combines a genetic algorithm (GA), with a Response Surface Approximation (RSA) of the Artificial Neural Network (ANN) type. During the optimization process, the individual objectives and constraints are approximated using ANN that is trained and tested using a few three-dimensional CFD flow simulations; the latter are obtained using the commercial CFD package Ansys-Fluent. To minimize three-dimensional effects, the stator and rotor stacking curves are taken as the design variable. They are parametrically represented using a quadratic rational Bézier curve (QRBC) whose parameters are directly and explicitly related to the blade lean, sweep and bow, which are used as the design variables. In addition, a noble representation of the stagger angle in the spanwise direction is introduced. The described strategy was applied to optimize the performance of the E/TU-3 axial turbine stage which is designed and tested in Germany. The optimization objectives introduced the isentropic efficiency and the streamwise vorticity, subject to some constraints. This optimization strategy proved to be successful, flexible and practical, and resulted in remarkable improvements in stage performance.
The application of throughflow optimisation to the design of radial and mixed flow turbines
2010
Radial and mixed flow turbines are important components of turbochargers in automotive engines. Their aerodynamic design is generally compromised by severe mechanical constraints, to deal with high temperature and unsteady operation, but also by the requirement of low inertia for rapid turbocharger response from low engine speed. Conventionally, the designer deals with these constraints in the preliminary design, using a high degree of empiricism, followed by extensive CFD analysis and geometry optimisation. This paper describes a new approach to the preliminary design using a quasi-3D throughflow method coupled to an optimiser, which allows a more rapid consideration of the design issues before moving on to 3D CFD analysis. The throughflow-based optimisation system was able to increase efficiency by over 3% at the same inertia or to reduce inertia by 20-30% at the same efficiency, compared to a baseline design.
Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy
In this paper, we present the computed flow results for those endwall designs produced using the automated non-axisymmetric endwall design procedure and target objective functions detailed in Part 1 of this paper, and where available, compare these with experimental measurements made using the CSIR low-speed research turbine used as the test case for the designs. Experimental measurements were taken immediately aft (X3) as well as downstream (X4) of the rotor row using a drilled 5-hole elbow probe, and both the computed as well as physical results were processed identically to ensure as high a degree of comparability between the computed and physical datasets. For the two initial cases (the η tt- and C ske-based designs), the results of the experiments confirmed the predictions of the simulations, although unexpected flow separations which were not predicted by the computational fluid dynamics (CFD) resulted in poorer agreement for the two remaining contoured cases. In general, the ...
2010
This study examines the results of a CFD and rotating experiment, comparing an annular and a generic end wall design for a model turbine rotor in a 1½ stage turbine at the CSIR, in an attempt to draw some conclusions regarding the proper selection of objective functions during the optimisation process. The CSIR has a rich body of experimental and computational data from a rotating test rig with both profiled and planar end walls, which provides an ideal opportunity to examine the validity of various objective functions. A 1½ ...
The design of three-dimensional turbine blades combined with profiled endwalls
Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy, 2008
This paper describes a novel design for reducing secondary flow in turbines. The design builds on previous work on non-axisymmetric profiled endwalls by combining them with three-dimensional blade design. Profiled endwalls have been shown to effectively reduce secondary flow but have often been used as a 'retrofit' application where the blade design is left unchanged. In the current paper reverse compound lean is used to prepare the blade row for the application of profiled endwalls. Computational fluid dynamic predictions ofthe expected performance show benefits over and above those of applying profiled endwalls to the blade row alone. The paper describes the design of the novel geometry for the so-called 'Durham Cascade' and gives predictions of the expected performance.