Associate Fellow AIAA Research Articles

Influence of far-field boundary on the calculated flowfield and performance of rotors

A experiment was conducted to demonstrate the influence of the physical location of the far-field boundary on the calculated performance and flowfield of a two-dimensional Darrieus rotor. A substantial sensitivity to the extent of the computational domain was noted and a series of calculations and comparisons with other approaches are presented to show the influence on pressure recovery and power estimates. Although the study was restricted to the case of a rotor, the sensitivity to far-field boundary will be of concern to the computation of other momentum devices. Introduction A two-dimensional Darrieus wind turbine, facing a uniform wind and spinning in the anticlockwise direction, is assumed to be placed at the center of a Cartesian domain. The computational domain is subdivided into control volumes by a series of orthogonal grid lines. The rotor-blades paths are circular in any horizontal plane. The velocity and presure field were obtained by solving steady, laminar, incompressible, NavierStokes equations using a primative variable finite-difference procedure known as SIMPLER. The influence of the spinning turbine blades was introduced as momentum source terms Sx and Sy (not known a priori) in the conservation equations. These terms are zero everywhere except at the circle described by the path of the blades. Rajagopalan and Fanucci proved this approach to be feasible in an application to inviscid flow around a two-dimensional vertical axis wind turbine in cylindrical coordinates, and further validation was obtained by Paraschivoiu et al. who compared the predictions with experiments after including dynamic stall effects. In functional notation, for a time-averaged calculation, the source terms can be written as Sx = Sx(Ci,Cd,a,Yabs,<*,R,e,c,p9B) (la) Sy = Sy(Cl9Cd9a9Yabs9u9R,0,c,p,B) (Ib) where Q and Cd are airfoil characteristics of the turbine blade, o: is the angle of attack of the blade to the relative velocity vector, Yabs is the absolute velocity of the fluid at the location (R ,6), co is the angular velocity of the rotor, c is the chord of the blade, and B is the number of blades. The dependence of Received July 6, 1987; presented as Paper 87-2284 at the AIAA 5th Applied Aerodynamics Conference, Monterey, CA, Aug. 17-19, 1987; synoptic received March 21, 1989. Copyright © 1989 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. Full paper available at AIAA Library, 555 W. 57th St., New York, NY 10019. Price: microfiche, $4.00; hard copy, $9.00. Remittance must accompany order. *Assistant Professor, Aerospace Engineering Department. Member AIAA. tProfessor, Aerospace Engineering Department. Associate Fellow AIAA. Sx and Sy on Reynolds number is considered only implicitly through the airfoil sectional characteristics C/ and Cd. The source terms, evaluated using the procedure illustrated in Ref. 2, resolved for Cartesian directions are

The Effect of Nonlinear Heat Conduction on the Pressure-Coupled Response of Solid Propellants

A ZELDOVICH-NOVOZHILOV model for the pressurecoupled response of solid propellants was developed with heat conduction in the condensed phase governed by a relaxation time, non-Fourier relation. Results indicate that, although the relaxation time appears in a frequency-squared relaxation time product combination, the non-Fourier model has negligible effect on the response in the frequency domain of interest to combustion instability for reasonable values of relaxation time. For large values of this parameter, the resonance is shifted to lower frequencies, reduced in magnitude, and narrowed. Presented as Paper 82-1102 at the AIAA/SAE/ASME 18th Joint Propulsion Conference, Cleveland, Ohio, June 21-23, 1982; submitted June 25, 1982; synoptic received July 5, 1983. Copyright © American Institute of Aeronautics and Astronautics, Inc., 1982. All rights reserved. Full paper available from AIAA Library, 555 W. 57th Street, New York, N.Y. 10019. Price: Microfiche, $4.00; hard copy, $8.00. Remittance must accompany order. * Graduate Student, School of Aeronautics and Astronautics (currently, Engineer, Morton Thiokol, Inc., Huntsville, Ala.). Student Member AIAA. tSenior Researcher, School of Aeronautics and Astronautics. Associate Fellow AIAA.