Stanford University Department of Aeronautics & Astronautics Aerospace Computing Laboratory
Contents Ongoing Projects · Completed Projects ·

Ongoing Projects

  • Effects of High Order Boundary Representation on LES Accuracy : Manuel Lopez

  • High Fidelity Modeling of Viscous Flow Phenomena for Conservation Laws : David Williams

Completed Projects

  • Spectral Difference Method for Incompressible Viscous Flow : Patrice Castonguay

  • Aerodynamics of hard disk drives and Vortex suppression of flow past bluff bodies : Andre Chan

  • Geometry Parameterization and Automation for CFD : Edmond Chiu

  • Airfoil optimization and genetic algorithm : Matt Culbreth

  • Supersonic Biplane Design via Adjoint Method : Rui Hu

    In developing the next generation supersonic transport airplane, two major challenges must be resolved. The fuel efficiency must be significantly improved, and the sonic boom propagating to the ground must be dramatically reduced. Both of these objectives can be achieved by reducing the shockwaves formed in supersonic flight. The Busemann biplane is famous for using favorable shockwave interaction to achieve nearly shock-free supersonic flight at its design Mach number. Its performance at off-design Mach numbers, however, can be very poor.
    We study the performance of supersonic biplane airfoils at design and off-design conditions. The choked flow and flow-hysteresis phenomena of these biplanes are studied. These effects are due to finite thickness of the airfoils and non-uniqueness of the solution to the Euler equations, creating over an order of magnitude more wave drag than that predicted by supersonic thin airfoil theory. As a result, the off-design performance is the major barrier to the practical use of supersonic biplanes.
    We improve the off-design performance of supersonic biplanes using adjoint based aerodynamic optimization technique. The Busemann biplane is used as the baseline design, and we alter its shape to achieve optimal wave drags in series of Mach numbers ranging from 1.1 to 1.7, during both acceleration and deceleration conditions. The optimized biplane airfoils dramatically reduces the effects of the choked flow and flow-hysteresis phenomena, while maintaining a certain degree of favorable shockwave interaction effects at the design Mach number. Compared to a diamond shaped single airfoil of the same total thickness, the wave drag of our optimized biplane is lower at almost all Mach numbers, and is significantly lower at the design Mach number. In addition, by performing a Navier-Stokes solution for the optimized airfoil, we find that the optimized biplane improves the total drag, including the wave drag and the viscous drag, compared to a single diamond airfoil.

  • Adjoint method and Modelling of Turbulent Flow Transition : Jen-Der Lee

  • Three-dimensional Spectral Difference High-order Accurate Unstructured Compressible Viscous Solver with Shock Capturing Ability and Large Eddy Simulation: Chunlei Liang

    The Spectral Difference (SD) method combines the salient feautures of structured and unstructured grid methods to achieve high computational efficiency and geometric flexibility. Similar to the discontinuous Galerkin (DG) and spectral volume (SV) methods, the SD scheme achieves high-order accuracy by locally approximating the solutions as a high degree polynomial inside each cell. One-dimensional Riemann solvers are employed to deal with the levels of interface jumps. Most importantly, being based on the differential form of the equations, SD formulation is simpler than that of the DG and SV methods as no test function or surface integral is involved. Conservation properties are still maintained by a judicious placement of the nodes at quadrature points of the chosen unstructured simplex.
    SD method is also being applied to study a few classical turbulent flow simulation testing cases.

  • Edge-based Meshless Methods for Compressible Flow Simulations : Aaron Katz

  • Development of a high-order spectral difference method for fluid-structure interaction and computational flapping wing aerodynamics: Kui Ou

  • Implicit and p-multigrid method for the spectral difference unstructured compressible viscous solver: Sachin Premasuthan

    The convergence of Spectral Difference method for viscous Navier-Stokes equations can be accelerated using both implicit Lower-Upper Symmetric Gauss-Seidl (LU-SGS) relaxation method and p-multigrid approach. Blending implicit and p-multigrid approaches, the speedup is achieved in the order of 10 to 100.

  • Time Spectral Method for Rotorcraft Flow with Vorticity Confinement: Nawee Butsuntorn

    By utilizing the periodic nature of the rotorcraft flow field, the Fourier based Time Spectral method lends itself to rotorcraft simulation and significantly increases the rate of convergence compared to traditional implicit time integration schemes such as the second order backward difference formula (BDF). Simulation of helicopter flows can adhere to engineering accuracy without the need of massive computing resources or long turnaround time by choosing an alternative framework for rotorcraft simulation. The method works in both hovering and forward flight regimes and has shown to be more computationally efficient and sufficiently accurate.

    A Vorticity Confinement method is under investigation and has been shown to work well in subsonic and transonic simulations. Vortical structure can be maintained after long distances without resorting to the traditional mesh refinement technique.

  • Multidisciplinary Design Optimization (MDO) of Supersonic Business Jet using Approximation Models: Hyoung S. Chung

    The recent growth of MDO concept to exploit the synergism of mutually interacting phenomena among different disciplines increases the computational burden and complexity of the design process. To solve these problems, an alternative using approximation models to the actual high-fidelity analysis code is getting increased attention as a necessity of MDO process. Currently, the advantages and disadvantages of various approximation models such as Response Surface and Kriging methods are being investigated. Research focuses on improving those methods so that they can be effectively incorporated in MDO process for aircraft design.

  • Parallel Unstructured AMR Scheme in Quiet Supersonic Platform Configuration: Seongim Choi

    Adaptive mesh refinement (AMR) is an advanced numerical technique gaining popularity in the scientific and engineering computing community for solving large-scale computing problems. The use of AMR techniques can significantly improve computational efficiency, and computer memory efficiency, by devoting finite computing resources (CPU time, memory) to the computational regions where they are most needed, making it possible to compute an accurate numerical solution with much less computing resources comparted to the use of a global fine mesh.

  • Computational Aeroelasticity in Turbomachinery: Hirofumi Doi

    Dynamic aeroelastic phenomenon such as flutter in Turbomachinery will be simulated by performing fluid/structural coupled computations. Combination of an unsteady flow solver for turbomachinery called TFLO and a finite element structural solver has been developed through transformation of loads and energy, deformation tracking mesh system, high order synchronization between the two solvers, etc.

  • The One-Equation Spalart-Allmaras Turbulence Model: Kaveh Hosseini

    The Spalart-Allmaras model is an eddy viscosity model. The eddy viscosity is directly solved from a transport equation rather than solving the kinetic energy of turbulence k, or any other quantity proportional to k, and defining eddy viscosity from it. Research focuses on a robust implementation of the One-Equation Spalart-Allmaras Turbulence Model in the 2D Navier-Stokes flow solver FLO103. The main difficulty is that this turbulence model's convergence is very sensitive especially in the case of explicit flow solvers.

  • An Implicit-Explicit Hybrid Scheme for Calculating Complex Unsteady Flows: John Hsu

    In current practice, unsteady flow simulations for turbomachinery are performed using a dual-time-stepping scheme. This work is motivated by the need to solve the time-accurate Navier-Stokes equations with greatly decreased computational cost. The purpose of this research is to investigate the introduction of an initial ADI step, guaranteeing second order accuracy in time, followed by a small number of cycles of the dual-time-stepping scheme augmented by multigrid. The O(delta t^2) accuracy in time should be retained without the need for large numbers of inner iterations required for convergence of typical iterative methods. The details of this new scheme are presented in this research while examples are given to demonstrate the second order accuracy and the convergence properties of the scheme.

  • Design Optimization of High-Lift configurations Using a Viscous Adjoint-Based Method: Sangho Kim

    Current research focuses on two-dimensional high-lift aerodynamic optimization using a continuous adjoint method. The adjoint method is extremely efficient since the computational expense incurred in the calculation of the complete gradient with respect to an arbitrary number of design variables is effectively independent of the number of design variables. Aerodynamic design using the Reynolds Averaged Navier-Stokes equations as the flow model has recently been performed for a single element airfoil and the accuracy of the gradient information from this method has also been proved.

  • Non-Linear Frequency Domain Method in 3-D: Ki Hwan Lee

    The main focus of this work is to apply Frequency Domain Method (FDM) to the non-linear unsteady flow solver in 3-D. The ability to calculate rough approximations in 3-D, comparable to the accuracy of experimental data, would allow us the initial data that are theoretically solid and at the same time, render faster convergence to steady state.

  • Reduced Order Modeling: Patrick LeGresley

    Research focuses on the development of reduced order models for use in design and optimization. To be computationally feasible the order of some systems, such as an aeroelastic system with millions of degrees of freedom, may need to be reduced. I am currently investigating the use of Proper Orthogonal Decomposition (POD) as a means to construct linear based models, with the ultimate goal of applying these models to Aerodynamic Shape Optimization (ASO) and Multidisciplinary Design Optimization (MDO) problems.

  • Aerodynamic Shape Optimization of Wings including Planform Variations: Kasidit Leoviriyakit

    Current reseach focuses on the formulation of optimization techniques based on control theory for aerodynamic shape design in inviscid compressible flow modeled by the Euler equations. The design methodology has been extended to include wing planform optimization. A model for the structure weight has been included in the design cost function to provide a meaningful design. A practical method to combine the structural weight into the design cost function has been studied. Results of optimizing a wing-fuselage of a commercial transport aircraft show a successful trade of planform design, leading to meaningful designs. The on-going results also support the necessity of including the structure weight in the cost function.

  • Multidisciplinary Optimization: Joaquim Martins

    Research is in the area of multidisciplinary optimization applied to aircraft design. The focus is on the use of high-fidelity models in aerodynamic and structural analysis and on the coupling of these two disciplines. Efficient calculation of sensitivities in these analyses is also part of this research.

  • Computational Methods for Analysis and Design of Aircraft: Georg May

    Research focuses on computational methods for the design of aircraft, such as aerodynamic shape optimization via control theory, using the adjoint method, and advanced techniques in computational fluid dynamics. It involves topics related to multigrid methods in an unstructured mesh environment. In particular an efficient algorithm for the automatic generation of a sequence of coarse meshes from a given fine mesh, which at the same time allows a control of the quality of the meshes, has been developed, implemented and tested. This algorithm is based on the edge collapsing technique, which uses repeated deletion of edges and update of the data structure for a given mesh to achieve a well controlled coarsening. It also investigate techniques for mesh optimization.

  • Unsteady Navier-Stokes Computations: Matt McMullen

    Research focuses on the efficient computation of solutions to the unsteady Navier-Stokes equations. Current focus is on the application of harmonic balance techniques to steady state solvers. Efficiency comparisons will be generated between frequency and time domain computations. The research will generate a new class of solvers which will be validated on low Reynolds number flows.

  • Aerodynamic Shape Optimization Techniques Based on Control Theory: Siva Nadarajah

    Research focuses on the following three topics. First, the study of the trade-off between the complexity of the discretization of the adjoint equation for both the continuous and discrete approach, the accuracy of the resulting estimate of the gradient, and its impact on the computational cost to approach an optimum solution. Second, the development of the unsteady adjoint equation. Optimal control of time dependent trajectories require the solution of the adjoint equation in reverse time from a final boundary condition. The research will produce unsteady adjoint algorithms for the optimization of a blade shape for a helicopter rotor to minimize the average drag over a complete revolution. Similar techniques can also be used to reduce radiated noise from aircraft engines. Third, the development of an adjoint method for the calculation of non-collocated sensitivities in supersonic flow. The goal is to develop a set of discrete adjoint equations and their corresponding boundary conditions in order to quantify the influence of geometry modifications on the pressure distribution at an arbitrary location within the domain of interest.

  • Surf the Non-Linear Wave: Sriram Shankaran

    Develop a numerical wind tunnel facility to predict the physics of tightly coupled aerodynamic and flexible membranes. Using this tool as a "sensor" in a design loop, "shape" changes to the membrane are estimated, thereby achieving desired performance goals. The eventual aim of this research is to develop a robust design methodology for flexible membrane-like-structures under the influence of aerodynamic forces, with possible applications to the design of sails for short-boards or yachts.

  • Aeroelasticity, Viscous Simulations, and Automatic Mesh Generation: Ryan Vartanian

    Research investigates methods for automatic mesh generation around arbitrary shape configurations. Complex configurations (such as high lift systems, automobiles, etc.) currently present immense difficulties to researchers in computational aerodynamics due to mesh generation problems. Programs like CART3D allow for solution of these configurations for the Euler equations. However, solutions for the Navier-Stokes equations require fine mesh resolution near the boundary, and cartesian methods often require a prohibitive number of cells to accurately resolve boundary layer effects. This research is in the process of developing a solution to this problem by generating body-fitted unstructured meshes that have desirable orthogonality, smoothness, and cell volume properties. This algorithm is currently in its early stages, but the current methods look promising.