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Author: Huang Huang (Aerospace engineer) Publisher: ISBN: Category : Computational fluid dynamics Languages : en Pages : 202
Book Description
The high-dimensional harmonic balance (HDHB) method has recently become popular in the field of periodic unsteady flow prediction due to its accuracy and high efficiency. In the present dissertation research, two and three-dimensional parallelized computational fluid dynamic (CFD) codes based on the HDHB method are developed and validated for unsteady turbulent flows. It is found that the stability condition for an explicit solver is highly dependent on the reduced grid frequency, a non-dimensional parameter that depends on the grid size, characteristic wave speed, and the highest frequency retained in the harmonic balance solver. Furthermore, for certain moderately and highly nonlinear problems, the pseudo-spectral operator used in the HDHB method is found to introduce aliasing errors, which may lead to nonlinear instabilites or non-physical solutions. As a remedy, a temporal spectral viscosity operator is proposed for de-aliasing purpose so as to stabilize HDHB solver. The proposed method is validated for a simple nonlinear Duffing oscillator case and laminar vortex shedding over an oscillating circular cylinder at Re=500. Another focus of this research is the design optimization of the turbomachinery blades for unsteady flows. The "steady state" nature of the HDHB technique makes it very-well suited for an adjoint sensitivity analysis mainly due to the fact that the storage requirements are greatly reduced. To date, the investigators have used the adjoint technique mainly for steady shape optimization. To the author's best knowledge, the technique has not been applied for unsteady design optimization of turbomachinery blades. In this dissertation, a discrete adjoint HDHB method is employed for unsteady turbomachinery shape optimization. With the help of the automatic differentiation (AD) tool, TAPENADE, the development time for an optimization solver can be reduced substantially. Both inverse design and optimization problems are considered to validate the optimization solver.
Author: Huang Huang (Aerospace engineer) Publisher: ISBN: Category : Computational fluid dynamics Languages : en Pages : 202
Book Description
The high-dimensional harmonic balance (HDHB) method has recently become popular in the field of periodic unsteady flow prediction due to its accuracy and high efficiency. In the present dissertation research, two and three-dimensional parallelized computational fluid dynamic (CFD) codes based on the HDHB method are developed and validated for unsteady turbulent flows. It is found that the stability condition for an explicit solver is highly dependent on the reduced grid frequency, a non-dimensional parameter that depends on the grid size, characteristic wave speed, and the highest frequency retained in the harmonic balance solver. Furthermore, for certain moderately and highly nonlinear problems, the pseudo-spectral operator used in the HDHB method is found to introduce aliasing errors, which may lead to nonlinear instabilites or non-physical solutions. As a remedy, a temporal spectral viscosity operator is proposed for de-aliasing purpose so as to stabilize HDHB solver. The proposed method is validated for a simple nonlinear Duffing oscillator case and laminar vortex shedding over an oscillating circular cylinder at Re=500. Another focus of this research is the design optimization of the turbomachinery blades for unsteady flows. The "steady state" nature of the HDHB technique makes it very-well suited for an adjoint sensitivity analysis mainly due to the fact that the storage requirements are greatly reduced. To date, the investigators have used the adjoint technique mainly for steady shape optimization. To the author's best knowledge, the technique has not been applied for unsteady design optimization of turbomachinery blades. In this dissertation, a discrete adjoint HDHB method is employed for unsteady turbomachinery shape optimization. With the help of the automatic differentiation (AD) tool, TAPENADE, the development time for an optimization solver can be reduced substantially. Both inverse design and optimization problems are considered to validate the optimization solver.
Author: Benjamin Walther Publisher: ISBN: Category : Languages : en Pages :
Book Description
"This work proposes a framework for fully-automatic gradient-based constrained aerodynamic shape optimization in a multistage turbomachinery environment. A turbomachinery solver which solves the Reynolds-averaged Navier-Stokes (RANS) equations to a steady-state in both rotating and stationary domains is developed. Characteristic-based inlet and outlet boundary conditions are imposed, while adjacent rotor and stator rows are coupled by mixing-plane interfaces. To allow for an efficient but accurate gradient calculation, the turbomachinery RANS solver is adjointed at a discrete level. The systematic approach for the development of the discrete adjoint solver is discussed. Special emphasis is put on the development of the turbomachinery specific features of the adjoint solver, i.e. on the derivation of flow-consistent adjoint inlet and outlet boundary conditions and, to allow for a concurrent rotor-stator optimization and stage coupling, on the development of an exact adjoint counterpart to the non-reflective, conservative mixing-plane formulation used in the flow solver. The adjoint solver is validated by comparing its sensitivities with finite-difference gradients obtained from the flow solver. A parallelized, automatic grid perturbation scheme utilizing radial basis functions, which is accurate and robust as well as able to handle complex multi-block grid configurations, is employed to calculate the gradient from the adjoint solution. A sequential quadratic programming algorithm is utilized to determine an improved blade shape based on the gradient information. The functionality of the proposed optimization method is demonstrated by the redesign of two different transonic compressor configurations. The design objective is to maximize the isentropic efficiency while constraining the mass flow rate and the total pressure ratio. The influence of the constraints on the design problem is investigated by comparing the results with those of an unconstrained optimization." --
Author: Vadivel Kumaran Sivashanmugam Publisher: ISBN: Category : Languages : en Pages : 122
Book Description
Aero-structural optimization of gas turbine blades is a very challenging task, given e.g. three dimensional nature of the flow, stringent performance requirements, structural and manufacturing considerations, etc. The current research work addresses this challenge by development and implementation of structural shape optimization module and integrating it with an aerodynamic shape optimization module to form an automated aero-structural optimization procedure. The optimizer combines a Multi-Objective Genetic Algorithm (MOGA), with a Response Surface Approximation (RSA) of the Artificial Neural Network (ANN) type. During the optimization process, each objective function and constraint is approximated by an individual ANN, which is trained and tested using an aerodynamic as well as a structure database composed of a few high fidelity flow simulations (CFD) and structure analysis (CSD) that are obtained using ANSYS Workbench 11.0. Addition of this multiple ANN technique to the optimizer greatly improves the accuracy of the RSA, provides control over handling different design variables and disciplines. The described methodology is then applied to the aero-structural optimization of the E/TU-3 turbine blade row and stage at design conditions to improve the aerodynamic and structural performance of the turbomachinery blades by optimizing the stacking curve. The proposed methodology proved quite successful, flexible and practical with significant increase in stage efficiency and decrease in equivalent stress.
Author: Seyyed Arash Mousavi Publisher: ISBN: Category : Languages : en Pages :
Book Description
"This research work presents an adjoint approach to optimize the aero-thermalproperties of gas turbine blades. The flow solver is a Reynolds-Averaged Navier-Stokes code applicable to structured grids. The flow governing equations are discretizedusing a second-order finite-volume scheme and for artificial dissipation, theJameson-Schmidt-Turkel (JST) scheme is applied in order to accurately capture theflow discontinuities. The code uses a five-stage modified Runge-Kutta explicit temporaldiscretisation and utilizes the multigrid method, residual smoothing and thelocal time stepping for convergence acceleration.A loosely coupled conjugate heat transfer (CHT) method is applied to considerthe effect of the internal convective cooling and obtain the fluid-solid interface temperatureat the blade surface. A finite-element solver is developed to solve the energyequation in the solid domain and the governing equation is solved by implementingthe weak-Galerkin finite-element discretization scheme where an unstructured lineartriangular mesh is adopted for the solution domain. The temperature at the solid andfluid interface is computed through an iterative exchange of the boundary conditionsacross the interface using the Flux Forward Temperature Back (FFTB) method. Forexternally cooled blades, a source term injection model is implemented to model theeffect of external cooling on the blade surface heat transfer.The optimization procedure is gradient-based and the blade shape optimizationis accomplished through SNOPT, a sequential-quadratic programming package thatis capable of automatically handling the linear and/or non-linear flow and geometric constraints. To efficiently calculate the gradients, a continuous adjoint method isemployed and in order to be consistent with the flow boundary condition, a characteristicbased approach is utilized in developing the adjoint boundary conditions.The flow solver is validated for several benchmark turbomachinery cascades.The optimization procedure is applied to several inviscid and viscous turbine andcompressor blades to enhance the aerodynamic and/or thermal performance. Thedeveloped optimization algorithm is demonstrated to be efficient in terms of computationaltime and accuracy for the optimization of two-dimensional turbomachinerycases where it provides promising results in reducing the desired objective functionswhile respecting the imposed flow and geometric constraints." --
Author: Pavan Kumar MV Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
The most critical parts of a gas turbine engine are turbine blades and disc. They are designed to operate under severe conditions such as high turbine inlet temperature, high speeds, and high compression ratios. Owing to these operating conditions high rotational speed which is likely to be between 60000 and 100000 rev/min. Design optimization of fluid machinery based on computer simulation has become a reality today because of development of high speed. Highly complex flow patterns are being predicted by solving mass, momentum and energy equations and near accurate solutions at an acceptable level can be achieved. The present work aims at optimizing the blade shape and analysis of surrogate model of turbine blade. The sweep and lean variables are modified to enhance the efficiency, based objective. RANS equations are solved to get the flow field and objective function values. Based neural network, model has been constructed and the blade shape has been modified to enhance performance. The surrogate performances are evaluated for applicability in turbo machinery blade.
Author: Publisher: ISBN: Category : Languages : en Pages : 14
Book Description
A method is presented to perform aerodynamic design optimization of turbomachinery blades. The method couples a Navier-Stokes flow solver with a grid generator and numerical optimization algorithm to seek improved designs for transonic turbine blades. A fast and efficient multigrid, finite-volume flow solver provides accurate performance evaluations of potential designs. Design variables consist of smooth perturbations to the blade surface. A unique elliptic-hyperbolic grid generation method is used to regenerate a Navier-Stokes grid after perturbations have been added to the geometry. Designs are sought which improve a design objective while remaining within specified constraints. The method is demonstrated with two transonic turbine blades with different types and numbers of design variables.
Author: Jason Charles Howison Publisher: ISBN: Category : Aeroelasticity Languages : en Pages : 165
Book Description
Most current wind turbine aeroelastic codes rely on the blade element momentum method with empirical corrections to compute aerodynamic forces on the wind turbine blades. While efficient, this method relies on experimental data and does not allow designers much flexibility for alternative blade designs. Unsteady solutions to the Navier-Stokes equations offer a significant improvement in aerodynamic modeling, but these are currently too computationally expensive to be useful in a design situation. However, steady-state solutions to the Navier-Stokes equations are possible with reasonable computation times. The harmonic balance method provides a way to represent unsteady, periodic flows through coupled a set of steady-state solutions. This method offers the possibility of unsteady flow solutions at a computational cost on the order of a few steady-state solutions. By coupling a harmonic balance driven aerodynamic model with a mode shape-based structural dynamics model, an efficient aeroelastic model for a wind turbine blade driven by the Navier-Stokes equations is developed in this dissertation. For wind turbine flows, turbulence modeling is essential, especially in the transition of the boundary layer from laminar to turbulent. As part of this dissertation, the Spalart-Allmaras turbulence model and the gamma-Re theta-t transition model are included in the aerodynamic model. This marks the first time that this transition model, turbulence model, and the harmonic balance method have been coupled to study unsteady wind turbine aerodynamics. Results show that the transition model matches experimental data more closely than a fully turbulent model for the onset of both static and dynamic stall. Flutter is of particular interest as turbines continue to increase in size, and longer and softer blades continue to enter the field. In this dissertation, flutter is investigated for the 1.5 MW WindPACT rotor blade. The aeroelastic model created, which incorporates the harmonic balance method and a fully turbulent aerodynamic model, is the first of its kind for wind turbine flutter analysis. Predictions match those of other aeroelastic models for the 1.5 MW WindPACT blade, and the first flap wise and edgewise modes are shown to dominate flutter for the rotor speeds considered.
Author: James Reuther Publisher: ISBN: Category : Control theory Languages : en Pages : 37
Book Description
Abstract: "An aerodynamic shape optimization method that treats the design of complex aircraft configurations subject to high fidelity computational fluid dynamics (CFD), geometric constraints and multiple design points is described. The design process will be greatly accelerated through the use of both control theory and distributed memory computer architectures. Control theory is employed to derive the adjoint differential equations whose solution allows for the evaluation of design gradient information at a fraction of the computational cost required by prevous design methods [5, 4, 24, 18]. The resulting problem is implemented on parallel distributed memory architectures using a domain decomposition approach, an optimized communication schedule, and the MPI (Message Passing Interface) standard for portability and efficiency. The final result achieves very rapid aerodynamic design based on a higher order CFD method. In order to facilitate the integration of these high fidelity CFD approaches into future multi-disciplinary optimization (MDO) applications, new methods must be developed which are capable of simultaneously addressing complex geometries, multiple objective functions, and geometric design constraints. In our earlier studies [8, 9, 10, 11, 19, 15, 20, 21, 22, 23, 1], we coupled the adjoint based design formulations with unconstrained optimization algorithms and showed that the approach was effective for the aerodynamic design of airfoils, wings, wing-bodies, and complex aircraft configurations. In many of the results presented in these earlier works, geometric constraints were satisfied either by a projection into feasible space or by posing the design space parametrization such that it automatically satisfied constraints. Furthermore, with the exception of reference [9] where the second author initially explored the use of multipoint design in conjunction with adjoint formulations, our earlier works have focused on single point design efforts. Here we demonstrate that the same methodology may be extended to treat complete configuration designs subject to multiple design points and geometric constraints. Examples are presented for both transonic and supersonic configurations ranging from wing alone designs to complex configurations designs involving wing, fuselage, nacelles and pylons."
Author: Huang Huang (Aerospace engineer)
Author: Huang Huang (Aerospace engineer)
Author: Benjamin Walther
Author: Vadivel Kumaran Sivashanmugam
Author: Temesgen Teklemariam Mengistu
Author: Seyyed Arash Mousavi
Author: Mohsen Gharagozlou
Author: Pavan Kumar MV
Author: 
Author: Jason Charles Howison
Author: James Reuther