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  • 1
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    Simulation of Synthetic Jets in Quiescent Air Using Unsteady Reynolds Averaged Navier-Stokes Equations (2004)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: We report research experience in applying an Unsteady Reynolds-Averaged Navier-Stokes (URANS) solver for the prediction of time-dependent flows in the presence of an active flow control device. The configuration under consideration is a synthetic jet created by a single diaphragm piezoelectric actuator in quiescent air. Time-averaged and instantaneous data for this case were obtained at Langley Research Center, using multiple measurement techniques. Computational results for this case using one-equation Spalart-Allmaras and two-equation Menter s turbulence models are presented here along with comparisons with the experimental data. The effect of grid refinement, preconditioning and time-step variation are also examined.
    Keywords: Fluid Mechanics and Thermodynamics
    Type: AIAA Paper 2004-4967 , 22nd AIAA Applied Aerodynamics Conference and Exhibit; Aug 16, 2004 - Aug 19, 2004; Providence, RI; United States
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  • 2
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    Evaluation of a Second-Order Accurate Navier-Stokes Code for Detached Eddy Simulation Past a Circular Cylinder (2003)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: We evaluate the applicability of a production computational fluid dynamics code for conducting detached eddy simulation for unsteady flows. A second-order accurate Navier-Stokes code developed at NASA Langley Research Center, known as TLNS3D, is used for these simulations. We focus our attention on high Reynolds number flow (Re = 5 x 10(sup 4) - 1.4 x 10(sup 5)) past a circular cylinder to simulate flows with large-scale separations. We consider two types of flow situations: one in which the flow at the separation point is laminar, and the other in which the flow is already turbulent when it detaches from the surface of the cylinder. Solutions are presented for two- and three-dimensional calculations using both the unsteady Reynolds-averaged Navier-Stokes paradigm and the detached eddy simulation treatment. All calculations use the standard Spalart-Allmaras turbulence model as the base model.
    Keywords: Fluid Mechanics and Thermodynamics
    Type: AIAA Paper 2003-4085 , 21st AIAA Applied Aerodynamics Conference; Jun 23, 2003 - Jun 26, 2003; Orlando, FL; United States
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  • 3
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    Flow Control Analysis on the Hump Model with RANS Tools (2003)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: A concerted effort is underway at NASA Langley Research Center to create a benchmark for Computational Fluid Dynamic (CFD) codes. both unstructured and structured, against a data set for the hump model with actuation. The hump model was tested in the NASA Langley 0.3-m Transonic Cryogenic Tunnel. The CFD codes used for the analyses are the FUN2D (Full Unstructured Navier-Stokes 2-Dimensional) code, the structured TLNS3D (Thin-Layer Navier-Stokes 3-Dimensional) code, and the structured CFL3D code, all developed at NASA Langley. The current investigation uses the time-accurate Reynolds-Averaged Navier-Stokes (RANS) approach to predict aerodynamic performance of the active flow control experimental database for the hump model. Two-dimensional computational results verified that steady blowing and suction and oscillatory suction/blowing can be used to significantly reduce the separated flow region on the model. Discrepancies do exist between the CFD results and experimental data in the region downstream of the slot with the largest differences in the oscillatory cases. Overall, the structured CFD codes exhibited similar behavior with each other for a wide range of control conditions, with the unstructured FUN2D code showing moderately different results in the separated flow region for the suction and oscillatory cases.
    Keywords: Fluid Mechanics and Thermodynamics
    Type: AIAA Paper 2003-0218 , 41st Aerospace Sciences Meeting and Exhibit; Jan 06, 2003 - Jan 09, 2003; Reno, NV; United States
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  • 4
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    Time Integration Schemes for the Unsteady Navier-stokes Equations (2001)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: The efficiency and accuracy of several time integration schemes are investigated for the unsteady Navier-Stokes equations. This study focuses on the efficiency of higher-order Runge-Kutta schemes in comparison with the popular Backward Differencing Formulations. For this comparison an unsteady two-dimensional laminar flow problem is chosen, i.e., flow around a circular cylinder at Re = 1200. It is concluded that for realistic error tolerances (smaller than 10(exp -1)) fourth-and fifth-order Runge-Kutta schemes are the most efficient. For reasons of robustness and computer storage, the fourth-order Runge-Kutta method is recommended. The efficiency of the fourth-order Runge-Kutta scheme exceeds that of second-order Backward Difference Formula by a factor of 2.5 at engineering error tolerance levels (10(exp -1) to 10(exp -2)). Efficiency gains are more dramatic at smaller tolerances.
    Keywords: Fluid Mechanics and Thermodynamics
    Type: AIAA Paper 2001-2612 , 15th Computational Fluid Dynamics Conference; Jun 11, 2001 - Jun 14, 2001; Anaheim, CA; United States
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  • 5
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    A Boundary Condition for Simulation of Flow Over Porous Surfaces (2001)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: A new boundary condition is presented.for simulating the flow over passively porous surfaces. The model builds on the prior work of R.H. Bush to eliminate the need for constructing grid within an underlying plenum, thereby simplifying the numerical modeling of passively porous flow control systems and reducing computation cost. Code experts.for two structured-grid.flow solvers, TLNS3D and CFL3D. and one unstructured solver, USM3Dns, collaborated with an experimental porosity expert to develop the model and implement it into their respective codes. Results presented,for the three codes on a slender forebody with circumferential porosity and a wing with leading-edge porosity demonstrate a good agreement with experimental data and a remarkable ability to predict the aggregate aerodynamic effects of surface porosity with a simple boundary condition.
    Keywords: Fluid Mechanics and Thermodynamics
    Type: AIAA Paper 2001-2412 , 19th Applied Aerodynamics Conference; Jun 11, 2001 - Jun 14, 2001; Anaheim, CA; United States
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  • 6
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    A Comparison of the Predictive Capabilities of Several Turbulence Models using Upwind and Central-Difference Computer Codes (1993)
    In:  CASI
    Details
    Publication Date: 2019-07-10
    Description: Four turbulence models are described and evaluated for transonic flows using the upwind code CFL3D and the central-difference code TLNS3D. In particular, the effects of recent modifications to the half-equation model of Johnson-King are explored in detail, and different versions of the model are compared. This model can obtain good results for both two-dimensional (2D) and three-dimensional (3D) separated flows. The one-equation models of Baldwin-Barth and Spalart-Allmaras perform well for separated airfoil flows, but can predict the shock too far forward at the outboard stations of a separated wing. The equilibrium model of Baldwin-Lomax predicts the shock location too far aft for both 2D and 3D separated flows, as expected. In general, all models perform well for attached or mildly separated flows.
    Keywords: Fluid Mechanics and Thermodynamics
    Type: AIAA Paper 93-0192
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  • 7
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    The Current Status of Unsteady CFD Approaches for Aerodynamic Flow Control (2002)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: An overview of the current status of time dependent algorithms is presented. Special attention is given to algorithms used to predict fluid actuator flows, as well as other active and passive flow control devices. Capabilities for the next decade are predicted, and principal impediments to the progress of time-dependent algorithms are identified.
    Keywords: Fluid Mechanics and Thermodynamics
    Type: AIAA Paper 2002-3346 , 1st AIAA Flow Control Conference; Jun 24, 2002 - Jun 26, 2002; Saint Louis, MI; United States
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  • 8
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    Simulation of Unsteady Flows Using an Unstructured Navier-Stokes Solver on Moving and Stationary Grids (2005)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: We apply an unsteady Reynolds-averaged Navier-Stokes (URANS) solver for unstructured grids to unsteady flows on moving and stationary grids. Example problems considered are relevant to active flow control and stability and control. Computational results are presented using the Spalart-Allmaras turbulence model and are compared to experimental data. The effect of grid and time-step refinement are examined.
    Keywords: Fluid Mechanics and Thermodynamics
    Type: AIAA Paper 2005-5093 , 17th AIAA Computational Fluid Dynamics Conference; Jun 06, 2005 - Jun 09, 2005; Toronto, Ontario; Canada
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  • 9
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    Simulation of Synthetic Jets in Quiescent Air Using Unsteady Reynolds Averaged Navier-Stokes Equations (2006)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: We apply an unsteady Reynolds-averaged Navier-Stokes (URANS) solver for the simulation of a synthetic jet created by a single diaphragm piezoelectric actuator in quiescent air. This configuration was designated as Case 1 for the CFDVAL2004 workshop held at Williamsburg, Virginia, in March 2004. Time-averaged and instantaneous data for this case were obtained at NASA Langley Research Center, using multiple measurement techniques. Computational results for this case using one-equation Spalart-Allmaras and two-equation Menter's turbulence models are presented along with the experimental data. The effect of grid refinement, preconditioning and time-step variation are also examined in this paper.
    Keywords: Fluid Mechanics and Thermodynamics
    Type: AIAA Journal; 44; 2; 217-224
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  • 10
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    Re-evaluation of an Optimized Second Order Backward Difference (BDF2OPT) Scheme for Unsteady Flow Applications (2009)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Recent experience in the application of an optimized, second-order, backward-difference (BDF2OPT) temporal scheme is reported. The primary focus of the work is on obtaining accurate solutions of the unsteady Reynolds-averaged Navier-Stokes equations over long periods of time for aerodynamic problems of interest. The baseline flow solver under consideration uses a particular BDF2OPT temporal scheme with a dual-time-stepping algorithm for advancing the flow solutions in time. Numerical difficulties are encountered with this scheme when the flow code is run for a large number of time steps, a behavior not seen with the standard second-order, backward-difference, temporal scheme. Based on a stability analysis, slight modifications to the BDF2OPT scheme are suggested. The performance and accuracy of this modified scheme is assessed by comparing the computational results with other numerical schemes and experimental data.
    Keywords: Fluid Mechanics and Thermodynamics
    Type: LF99-8943 , AIAA Paper 2010-0122 , 48th AIAA Aerospace Sciences Meeting; Jan 04, 2010 - Jan 07, 2010; Orlando, FL; United States
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