Walter P. Wolfe

CFD calculations of S809 aerodynamic characteristics

Steady-state, two-dimensional CFD calculations were made for the S809 laminar-flow, wind-turbine airfoil using the commercial code CFD-ACE. Comparisons of the computed pressure and aerodynamic coefficients were made with wind tunnel data from the Delft University 1.8 m x 1.25 m low-turbulence wind tunnel. This work highlights two areas in CFD that require further investigation and development in order to enable accurate numerical simulations of flow about current generation wind-turbine airfoils: transition prediction and turbulence modeling. The results show that the laminar-to-turbulent transition point must be modeled correctly to get accurate simulations for attached flow. Calculations also show that the standard turbulence model used in most commercial CFD codes, the k-{epsilon} model, is not appropriate at angles of attack with flow separation.

Fluid motion inside a spinning nutating cylinder

The incompressible three-dimensional Navier–Stokes equations are solved numerically for a fluid-filled cylindrical cannister that is spinning and nutating. The motion of the cannister is characteristic of that experienced by spin-stabilized artillery projectiles. Equations for the internal fluid motion are derived in a non-inertial aeroballistic coordinate system. Steady-state numerical solutions are obtained by an iterative finite-difference procedure. Flow fields and liquid induced moments have been calculated for viscosities in the range of 0.9 × 10 4 −1 × 10 9 cSt. The nature of the three-dimensional fluid motion inside the cylinder is discussed, and the moments generated by the fluid are explained. The calculated moments generally agree with experimental measurements.

EXPERIMENTS AND COMPUTATIONS OF ROLL TORQUE INDUCED BY VORTEX-FIN INTERACTION

An experiment was conducted in Arnold Engineering Development Centers 16-ft transonic wind tunnel to measure the dependency of vortex-induced counter torque upon J (the ratio of spin motor jet dynamic pres- sure to freestream dynamic pressure), Mach number, Reynolds number, angle of attack and roll orientation, spin motor nozzle configuration, and fin cant angle. Counter torque data and Laser Vapor Screen images confirm that J is the dominant parameter for correlating counter torque produced by a given vehicle configura- tion, flight condition, angle of attack and roll orienta- tion. At M = 0.8 (with no shock waves in the flow), we observed a monotonic variation of the counter torque coefficient CCT with J that is independent of Reynolds number but dependent on angle of attack and the orientation of the fins with respect to the spin motor nozzle azimuthal location. At M = 0.95 and 1.1, meas- ured values of CCT were strongly influenced by changes in Reynolds number, suggesting that shock-boundary layer interaction may be present. Nomenclature A model cross-sectional area CCT counter torque coefficient, Eq. 4 CP center of pressure CT counter torque due to vortex-fin interaction D model diameter J plume-freestream interaction parameter,

An Overview of the Development of a Vortex Based Inflation Code for Parachute Simulation (VIPAR)

Sandia National Laboratories has undertaken an ambitious, multiyear effort to greatly improve our parachute system modeling and analysis capabilities. The impetus for this effort is twofold. First, extending the stockpile lifetime raises serious questions regarding the ability of the parachutes to meet their requirements in the future due to material aging. These aging questions cannot currently be answered using available tools and techniques which are based upon the experience of expert staff and full-scale flight tests and are, therefore, not predictive. Second, the atrophy of our parachute technology base and the loss of our experienced staff has eroded our ability to respond to any future problems with stockpiled parachutes or to rapidly design a new parachute system on an experience base alone. To assure a future in-house capability for technical oversight of stockpile nuclear weapon parachutes, Sandia must move from our present empirically based approach to a computationally based, predictive methodology. This paper discusses the current status of the code development and experimental validation activities. Significant milestones that have been achieved and those that are coming up in the next year are discussed.

Development of a massively parallel parachute performance prediction code

The Department of Energy has given Sandia full responsibility for the complete life cycle (cradle to grave) of all nuclear weapon parachutes. Sandia National Laboratories is initiating development of a complete numerical simulation of parachute performance, beginning with parachute deployment and continuing through inflation and steady state descent. The purpose of the parachute performance code is to predict the performance of stockpile weapon parachutes as these parachutes continue to age well beyond their intended service life. A new massively parallel computer will provide unprecedented speed and memory for solving this complex problem, and new software will be written to treat the coupled fluid, structure and trajectory calculations as part of a single code. Verification and validation experiments have been proposed to provide the necessary confidence in the computations.

Drag predictions for projectiles and finned bodies in incompressibleflow

A design method is presented for calculating the flowfield and drag of bodies of revolution, with and without aerodynamic surfaces, at zero angle of attack in incompressible flow. The body pressure distribution, viscous shear stress, and boundary-layer separation point are calculated by a combination of a potential-flow method and boundary-layer techniques. The potential solution is obtained by modeling the body with an axial distribution of source/sink elements whose strengths vary linearly along their length. Both the laminar and turbulent boundary-layer solutions use momentum integral techniques which have been modified to account for the effects of surface roughness. An existing technique for estimating the location of transition was also modified to include surface roughness. Empirical correlations are developed to estimate the base pressure coefficient for a wide variety of geometries. Body surface pressure distributions and drag predictions are compared with experimental data for artillery projectiles, conical bodies, bombs, and missiles. Very good agreement between the present method and experiment is obtained.

VFLOW2D - A Vorte-Based Code for Computing Flow Over Elastically Supported Tubes and Tube Arrays

A numerical flow model is developed to simulate two-dimensional fluid flow past immersed, elastically supported tube arrays. This work is motivated by the objective of predicting forces and motion associated with both deep-water drilling and production risers in the oil industry. This work has other engineering applications including simulation of flow past tubular heat exchangers or submarine-towed sensor arrays and the flow about parachute ribbons. In the present work, a vortex method is used for solving the unsteady flow field. This method demonstrates inherent advantages over more conventional grid-based computational fluid dynamics. The vortex method is non-iterative, does not require artificial viscosity for stability, displays minimal numerical diffusion, can easily treat moving boundaries, and allows a greatly reduced computational domain since vorticity occupies only a small fraction of the fluid volume. A gridless approach is used in the flow sufficiently distant from surfaces. A Lagrangian remap scheme is used near surfaces to calculate diffusion and convection of vorticity. A fast multipole technique is utilized for efficient calculation of velocity from the vorticity field. The ability of the method to correctly predict lift and drag forces on simple stationary geometries over a broad range of Reynolds numbers is presented.