Todd R. Quackenbush

Rotorcraft Interactional Aerodynamics with Fast Vortex/Fast Panel Methods

A Comprehensive Hierarchical Aeromechanics Rotorcraft Model, (CHARM), incorporating fast vortex and fast panel methods for modeling complete rotorcraft has been developed and applied to the problems of rotor/wake/body interaction, wind tunnel wall interference, and ground effect. Sample calculations are presented to demonstrate the capabilities of the fast methods in these modeling applications. Correlations with test data are described that illustrate the performance of the analysis in capturing measured values of average rotor performance, rotor-induced fuselage loading, and wake geometry associated with interactional aerodynamics phenomena. Results suggest that these fast methods can provide good accuracy for a wide variety of key interactional aerodynamics problems at computation times far less than finite volume/finite difference (FV/FD) CFD analyses.

New free-wake analysis of rotorcraft hover performance using influence coefficients

Free-wake analyses of helicopter rotor wakes in hover using time stepping have been shown to encounter instabilities which preclude convergence to valid free-vortex solutions for rotor-wake geometries. Previous work has demonstrated that these convergence difficulties can be overcome by implementing a new free-wake analysis method based on the use of influence coefficients. The present paper reviews this approach and documents its incorporation into a hover performance analysis called Evaluation of Hover Performance using Influence Coefficients (EHPIC). The technical principles underlying the EHPIC code are described with emphasis on steps taken to develop the single-filament wake models used in previous work into a multifilament wake valid for realistic hover performance predictions. The coupling of the wake model to a lifting surface loads analysis is described, and sample problems are solved that illustrate the robustness of the method. Performance calculations are also undertaken for hover to illustrate the utility of EHPIC in the analysis of rotorcraft performance.

Fast Three-Dimensional Vortex Method for Unsteady Wake Calculations

References Saad, Y., and Schultz, M. H., GMRES: A Generalized Minimal Residual Algorithm for Solving Nonsymmetric Linear Systems, Journal of the Science of Statistical Computations, Vol. 7, No. 3, 1986, pp. 856-869. Wigton, L. B., Yu, N. J., and Young, D. P., GMRES Acceleration of Computational Fluid Dynamics Codes, AIAA Paper 84-1494-CP, 1984. Sankar, L. N., and Tang, W., Numerical Solution of Unsteady Viscous Flow past Rotor Sections, AIAA Paper 85-0129, Jan. 1985. Hixon, R., and Sankar, L. N., Application of a Generalized Minimal Residual Method to 2D Unsteady Flows, AIAA Paper 92-0422, Jan. 1992. Steger, J. L., Implicit Finite Difference Simulation of Flow about Arbitrary Two-Dimensional Geometries, AIAA Journal, Vol. 18, No. 2, 1980, pp.159-167.

Predicting the Influence of Blade Shape on Hover Performance with Comprehensive Analyses

The ability to predict and understand the influence of rotor tip shape on hovering rotor performance is critical to rotorcraft development. Comprehensive rotorcraft analysis methods are an efficient way to reduce the risk and cost associated with developing new rotor designs. In the modern design environment, these methods are ideal for efficiently traversing the design space in order to identify designs of interest suitable for more detailed analysis, testing, and optimization. In this paper, the ability of three distinctly different comprehensive rotorcraft methods (EHPIC, CHARM, and VTM) to predict the hover performance of a rotor with a variety of tip shapes is evaluated. The assessment indicates that good predictive fidelity is achieved for the cases considered, though dependence on airfoil data remains a limiting factor in the generality of the analysis results.

Computational Simulation of High-Speed Steady Homogeneous Two-Phase Flow in Complex Piping Systems

A study was undertaken to predict steady flow conditions in two-phase steam/water flows in safety/relief discharge piping systems. The homogeneous-equilibrium model was used for the two-phase flow along with the ASME Steam Tables in subroutine form as a state equation. The approach can also accommodate single-phase flows of superheated steam or subcooled liquid. Subroutines were developed to simulate flows through isentropic area changes, abrupt area changes, adiabatic constant area pipes with friction, valves, two-phase shock waves, and mass addition at pipe junctions. These subroutines were combined to predict conditions in arbitrary complex piping systems. Sample calculations which treat both single line and multiple-branch piping systems are included.