Bulletin of the American Physical Society
62nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 54, Number 19
Sunday–Tuesday, November 22–24, 2009; Minneapolis, Minnesota
Session EW: Mini-Symposium on Uncertainty Quantification in Simulations of Fluid Flow |
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Chair: Gianluca Iaccarino, Stanford University Room: 208A-D |
Sunday, November 22, 2009 4:15PM - 4:41PM |
EW.00001: Scattering of shock waves by random roughness Invited Speaker: We employ second-order stochastic perturbation analysis and stochastic simulations synergistically to study supersonic flow past a rough wedge. The roughness is modeleed as stochastic process obtained from a new stochastic equation. We derive explicit formulas for the perturbed solution, which along with the stochastic simulation results aid to elucidate the physical scaling laws. For small roughness height and correlation length, the mean of the perturbed pressure scales quadratically with the height and the inverse correlation length while the corresponding variance scales linearly. Our results are useful in evaluating the effects of roughness in high-speed flight but also in designing novel enhanced-lift aerodynamic surfaces using rough skin concepts. [Preview Abstract] |
Sunday, November 22, 2009 4:41PM - 5:07PM |
EW.00002: Stochastic Dynamics Models for Laminar-to-Turbulent Transition on a Flight Vehicle Invited Speaker: Random pressure fluctuations within a turbulent boundary layer provide dynamic excitation to a flight vehicle. These random fluctuations must be adequately modeled and appropriately utilized by high fidelity structural dynamics finite element models in order to achieve accurate predictions of structural random vibration response. Most work in this area assumes the fluctuating pressure field to be fully turbulent. However, most flight vehicles experience a transition within the boundary layer from laminar to turbulent flow. This transition event also provides dynamic excitation to the vehicle, resulting in structural response that, for some systems, can be very significant. Herein, we provide a model for the pressure field acting on a flight vehicle in the laminar-to-turbulent transition zone for the purpose of predicting associated structural vibration response. The model is a Gaussian random field modulated by a Poisson field to capture the intermittent characteristics of turbulent flow in the transition zone. Computer algorithms to generate samples of the random pressure field are provided, and these samples are applied to a finite element model for a flexible beam with attached oscillator for illustration. [Preview Abstract] |
Sunday, November 22, 2009 5:07PM - 5:33PM |
EW.00003: Optimal design and uncertainty quantification in blood flow simulations for congenital heart disease Invited Speaker: Recent work has demonstrated substantial progress in capabilities for patient-specific cardiovascular flow simulations. Recent advances include increasingly complex geometries, physiological flow conditions, and fluid structure interaction. However inputs to these simulations, including medical image data, catheter-derived pressures and material properties, can have significant uncertainties associated with them. For simulations to predict clinically useful and reliable output information, it is necessary to quantify the effects of input uncertainties on outputs of interest. In addition, blood flow simulation tools can now be efficiently coupled to shape optimization algorithms for surgery design applications, and these tools should incorporate uncertainty information. We present a unified framework to systematically and efficient account for uncertainties in simulations using adaptive stochastic collocation. In addition, we present a framework for derivative-free optimization of cardiovascular geometries, and layer these tools to perform optimization under uncertainty. These methods are demonstrated using simulations and surgery optimization to improve hemodynamics in pediatric cardiology applications. [Preview Abstract] |
Sunday, November 22, 2009 5:33PM - 5:59PM |
EW.00004: Calibration, Validation and Uncertainty Quantification for Hypersonic Reentry Vehicles Invited Speaker: At the Center for Predictive Engineering and Computational Sciences at the University of Texas, we are engaged in an effort to characterize the uncertainties encountered in simulations of hypersonic reentry vehicles. Uncertainties arise from the modeling of several complex phenomena such as aerochemistry, thermal radiation, turbulence and ablation, and their interactions. Our approach to characterizing uncertainty is intimately connected to the process of determining uncertain model parameters through calibration and the assessment of model veracity through validation. The outlines of this approach will be described, including the use of Bayesian inference, treatment of uncertainty arising from modeling errors and validation criteria. As examples, application of this uncertainty quantification framework to several component problems will be described, including turbulence and chemical reaction mechanisms. Also discussed will be the sensitivities of simulations of a full-scale reentry vehicle to the various sources of uncertainties discussed above. [Preview Abstract] |
Sunday, November 22, 2009 5:59PM - 6:25PM |
EW.00005: Wind Tunnel to Flight: Numerical Simulations of Hypersonic Propulsion Systems Invited Speaker: Uncertainties in the flight conditions and limitations of ground based facilities create inherent difficulties in assessing the performance of hypersonic propulsion systems. We use numerical simulations to investigate the correlation of wind-tunnel measurements (Steelant et al., 2006) and flight data (Hass et al., 2005) for the HyShot vehicle; the objective is to identify potential engine unstart events occurring under different combustion regimes. As a first step we perform simulations corresponding to both reacting and non-reacting conditions in the ground-based facility to validate the numerical tools. Next, we focus on reproducing the flight conditions; a fundamental difficulty is the lack of precise information about the vehicle trajectory. A Bayesian inversion strategy is used to infer the altitude, angle of attack and Mach number from the noisy pressure measurements collected during the flight. The estimated conditions, together with the scatter due to the measurement uncertainty, are then used to study the flow and thermal fields in the combustor. The details of the methods used to characterize the uncertainty in the flow simulations and to perform the Bayesian inversion will also be discussed. [Preview Abstract] |
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