Rongqiao Wang

Optimization Strategy for a Shrouded Turbine Blade Using Variable-Complexity Modeling Methodology

This paper presents the development of a collaborative optimization framework in combination with a variable-complexity modeling technique for the multidisciplinary coupling analysis and design of a shrouded turbine blade. The multidisciplinary optimization design of the shrouded turbine blade involves a high-fidelity detailed computational model and medium-fidelity models, which can become prohibitively expensive. In this investigation, a variable-complexity modeling methodology is introduced, where low-fidelity models and a scaling function are used to approximate the medium- and high-fidelity models through the optimizers in an inner-loop optimization to reduce computational expense. The optimization framework developed includes the collaborative optimization process, parametric modeling of the shrouded turbine blade, fluid–structure interaction solver using arbitrary Lagrangian–Eulerian formulation, an adaptive hexahedral structure mesh generator by establishing virtual blocks and parametric fixed poi...

Research on Surrogate Model Based on Local Radial Point Interpolation Method

In order to increase the accuracy of surrogate models in structural reliability analysis, we put forward a kind of surrogate model based on local radial point interpolation method (LRPIM). Three kinds of radial basis function (RBF) are employed for the shape function construction to form different kinds of LRPIM model.In order to illustrate the approximating ability of each surrogate model, we build up a nonlinear function model and carry out a numerical experiment on gas turbine disk’s estimated life-span. Compared with polynomial model, Chebyshev orthogonal polynomial model, Kriging model and RBF neural network model, LRPIM model has a demonstrable difference in terms of accuracy. For different polynomial basis order with constant sampling nodes amount, we conclude that fluctuant accuracy can be described by the balance between the describing improvement brought by polynomial basis order increase and the local impairment brought by support domain expansion. For sampling nodes amount with constant polynomial basis order, we conclude that accuracy of LRPIM model improves when sampling nodes amount increases.In order to illustrate the potential in reliability analysis, we apply the best performing LRPIM model to a set of widely used test problems, which certifies the accuracy and robustness of this kind of surrogate model.In a word, LRPIM model is one of the most promising surrogate models compared with other models on nonlinear approximating problems and reliability analysis.Copyright

Fatigue Crack Growth of Multiple Load Path Structure Under Combined Fatigue Loading: Part II — Experiment Study

The fir-tree mortise of a turbine is a typical multiple load path structure which can reallocate the loading during operation. Performing experiments on a full scale turbine blade attached to a part of actual turbine disc at elevated temperature can present the reallocation phenomenon and accurately predict the crack growth of the fir-tree mortise under combined cycle fatigue (CCF). The purpose of this experiment is to determine the allowable crack size of this multiple load path structure under the circumstance of a firm overhaul period. The experimental load spectrum was determined by using a linear cumulative damage rule based on the flight load spectrum. And three turbine components were tested by using a Ferris Wheel system to access the effect of HCF loading amplitude on life. Then the experiments on crack growth were carried out to investigate crack growth lives of the actual mortise teeth with a pre-crack under combined cycle fatigue at elevated temperature. The effects of the contact state of the turbine mortise on crack propagation rates were investigated by comparing the turbine components with nominal dimensions and limiting dimensions. Fatigue fracture analysis by SEM certified that the failure was owing to combined cycle fatigue. Combined with numerical simulations, the crack growth behavior of the turbine components under combined cycle fatigue loading was estimated. Based on the above work, this paper provides a new way to establish a life-time criterion for withdrawal from service of turbine components.Copyright

Fatigue crack growth of multiple load path structure under combined fatigue loading: Part I Numerical simulation

A new numerical method for the analysis of fatigue crack growth in the multiple load path structure under low-high cycle combined fatigue (L-HCCF) loading is proposed in this paper. Firstly, vibrational stress is obtained through dynamic response analyses considering joint dry friction between the turbine blade and the turbine disc based on equivalent linearization and micro-slip model. Then, the crack growth in the fir-tree attachment is simulated under vibrational stress superimposed with low cycle fatigue loading through fracture mechanics (FM) analysis. Vibrational loading in the fir-tree attachment is redistributed with the crack propagation because of this multiple load path structure. Thus, dynamic response analysis is re-performed on the turbine attachment. At last, the crack growth life of multiple load path structure under L-HCCF loading is predicted based on the linear cumulative damage model. The predicted life agrees well with the experimental data of actual turbine component, which verifies that the new numerical method for the analysis of fatigue crack growth in the multiple load path structure under L-HCCF loading is reasonable and feasible.© 2014 ASME

Multidisciplinary Optimization Technology Research on Typical Turbine Assembly Structure

A multidisciplinary design optimization (MDO) method for turbine mortise assembly structure is presented. This method takes tenon and mortise as a whole to carry on the design optimization. With the adoption of Design of Experiment (DOE) method and Collaborative Optimization (CO) Strategy, this method has realized the coupling parallel optimization of the mortise assembly structure. To verify the effectiveness of the proposed method a typical fir-tree mortise structure design optimization is provided as an example. The results show that the mass and Von Mises Stress of the mortise assembly structure were reduced remarkably, which means that the proposed method has a significant role in enhancing structural performance.Copyright

Study on disk and blade design based on multi-layer optimization strategy

Multi-layer optimization strategy plays a key role on solving multi-discipline optimization design (MDO) on the turbine. The main principle of MDO firstly extends to component autonomy from disciplinary autonomy. Based on component and discipline autonomy, this paper designs four kinds of MDO framework which are applied on the turbine design combining with present MDO strategies including BLISS2000, CO and ATC. Both the two-layer including double-subsystem and two-layer including triple-subsystem are built by BLISS2000 strategy as the two-layer framework for turbine design, while the threelayer including triple-subsystem strategy takes full advantage of BLISS2000 and CO stra tegies. Additionally, due to introduction of auxiliary variables and associated variables, the ATC optimization strategy requires huge extra optimization cost, so it is not suitable for triple-layer MDO strategy on turbine. Finally, the integrated MDO of disk and blade tests the former three kinds of MDO strategies. The preponderance of the MDO strategies including three subsystems is higher efficiency, while complex interactions between layers always lead to worse optimization accuracy and efficiency on three layers strategy comparing with two layers strategy.

Experimental and Numerical Analysis of Microstructures and Stress States of Shot-Peened GH4169 Superalloys

Combining experiments and finite element analysis (FEA), a systematic study was performed to analyze the microstructural evolution and stress states of shot-peened GH4169 superalloy over a variety of peening intensities and coverages. A dislocation density evolution model was integrated into the representative volume FEA model to quantitatively predict microstructural evolution in the surface layers and compared with experimental results. It was found that surface roughness and through-depth residual stress profile are more sensitive to shot-peening intensity compared to coverage due to the high kinetic energy involved. Moreover, a surface nanocrystallization layer was discovered in the top surface region of GH4169 for all shot-peening conditions. However, the grain refinement was more intensified under high shot-peening coverage, under which enough time was permitted for grain refinement. The grain size gradient predicted by the numerical framework showed good agreement with experimental observations.

Effects of Heat-Treatment Residual Stress on Low Cycle Fatigue Life of a Turbine Disk in PM Superalloy

Turbine disks in powder metallurgy (PM) superalloy have been widely used in advanced aeroengines. The production of PM superalloy turbine disks involves a series of heat treatment processes, which would inevitably create residual stresses. It has been proved that the low cycle fatigue (LCF) life of the turbine disk is affected by the residual stresses. The computational simulation of heat treatment is considered as an effective way to evaluate the residual stresses in a turbine disk. A finite element software was used to simulate the heat-treatment processes of a FGH95 turbine disk to obtain the residual stress field.To investigate the relaxation of residual stress in FGH95, smooth bar specimens were measured by X-ray diffraction before and after being loaded. Modified by the residual stresses, SWT model is used to predict the low cycle fatigue life of the turbine disk modified by the residual stress field obtained from the simulation of heat treatment.By the comparison between the prediction modified by the residual stress and the prediction without modification, a considerable decrease in low cycle fatigue life is indicated.Copyright

Dominant Damage Factors Determining for Single Crystal Nickel Superalloys Under Cyclic Loading Based on Principal Component Analysis

A critical plane approach in combination with principal component analysis (PCA) for determining dominant damage factors (DDFs) was developed for single crystal nickel superalloys at elevated temperature. Maximum resolved shear stress (RSS), maximum slip rate and other 2 mesoscopic parameters on the critical plane, defined as the preferential slip plane, were selected as damage parameters. Correlation analysis results indicated that there were strong correlations (i.e. multicollinearity) among the selected parameters. To address this issue, PCA was performed to eliminate the effect of multicollinearity and the DDFs were determined as well. Based on the DDFs a life model was proposed and then validated by the fatigue experimental results. Most of the experimental lives are within the factor three of the predicted ones. The life model has a relatively simple form with reliable constants which facilitates the application in industry design.Copyright