James W. Purvis

Bio: James W. Purvis is an academic researcher from Sandia National Laboratories. The author has contributed to research in topics: Lift coefficient & Lift-induced drag. The author has an hindex of 6, co-authored 12 publications receiving 117 citations. Previous affiliations of James W. Purvis include United States Department of the Navy.

Analytical Prediction of Vortex Lift

Abstract: General integral expressions are derived for the nonlinear lift and pitching moment of arbitrary wing planforms in subsonic flow The analysis uses the suction analogy and an assumed pressure distribution based on classical linear theory results The potential flow lift constant and certain wing geometric parameters are the only unknowns in the integral expressions Results of the analysis are compared with experimental data and other numerical methods for several representative wings, including ogee and double-delta planforms The present method is shown to be as accurate as other numerical schemes for predicting total lift, induced drag, and pitching moment b c c CL CD Cm CT Cs cc, ccd E2 Nomenclature = aspect ratio = wing span =chord = reference length = lift coefficient = drag coefficient = pitching moment coefficient = thrust coefficient = suction coefficient = section lift coefficient = section induced drag coefficient = section suction coefficient = pressure loading coefficient = drag = proportionality constant, Eq (32) = proportionality constant, Eq (53) = chordwise function, Eq (44) ff(rj) = span wise f unction, Eq (28) K = potential constant L =lift loading constant, Eq (5) S = suction force SR = reference area s = suction force per unit length T = leading edge thrust, Eq (7) T' = leading edge thrust per unit length V = freestream speed Wj = downwash velocity component, Eq (11) a = angle of attack F = vorticity p = freestream density £ = nondimensional chordwise coordinate 77 = nondimensional spanwise coordinate A = leading edge sweep angle Subscripts P = potential flow E =edge / = induced VLE = leading edge vortex VSE = side edge vortex

Theoretical Analysis of Parachute Inflation Including Fluid Kinetics

Abstract: An analysis is presented for predicting parachute inflation. Equations of motion for the complete system are developed from first principles, and are solved with no experimental inputs. Ballistic equations of motion are derived for the canopy, payload, and suspension line masses. However, the enclosed fluid mass is not lumped with the canopy as an apparent mass term. Instead, the fluid conservation equations for a deforming, accelerating control volume are solved to determine the behavior of the captured fluid and its interaction with the canopy. Only first-order effects are included, and the analysis is limited to inviscid, incompressible flow. Results for both porous and nonporous canopies are compared with experimental data.

Armored garment for protecting

Abstract: A lightweight, armored protective garment for protecting an arm or leg from blast superheated gases, blast overpressure shock, shrapnel, and spall from a explosive device, such as a Rocket Propelled Grenade (RPG) or a roadside Improvised Explosive Device (IED). The garment has a ballistic sleeve made of a ballistic fabric, such as an aramid fiber (e.g., KEVLAR®) cloth, that prevents thermal burns from the blast superheated gases, while providing some protection from fragments. Additionally, the garment has two or more rigid armor inserts that cover the upper and lower arm and protect against high-velocity projectiles, shrapnel and spall. The rigid inserts can be made of multiple plies of a carbon/epoxy composite laminate. The combination of 6 layers of KEVLAR® fabric and 28 plies of carbon/epoxy laminate inserts (with the inserts being sandwiched in-between the KEVLAR® layers), can meet the level IIIA fragmentation minimum V 50 requirements for the US Interceptor Outer Tactical Vest.

Device for adapting continuously variable transmissions to infinitely variable transmissions with forward-neutral-reverse capabilities

Abstract: An infinitely variable transmission is capable of operating between a maximum speed in one direction and a minimum speed in an opposite direction, including a zero output angular velocity, while being supplied with energy at a constant angular velocity. Input energy is divided between a first power path carrying an orbital set of elements and a second path that includes a variable speed adjustment mechanism. The second power path also connects with the orbital set of elements in such a way as to vary the rate of angular rotation thereof. The combined effects of power from the first and second power paths are combined and delivered to an output element by the orbital element set. The transmission can be designed to operate over a preselected ratio of forward to reverse output speeds.

Prediction of Parachute Line Sail During Lines-First Deployment

Abstract: A numerical deployment simulation with the capability to predict line sail is presented. A finite-element approach is used in which both canopy and suspension lines are modeled as flexible, distributed-mass structures connected to a finite-mass forebody. The model includes all aspects of the deployment problem, such as suspension line aerodynamics, line ties, .and canopy/deployment bag friction. The model has been verified by comparison with experimental data and used to investigate proposed solutions for a system with a line sail problem.

The unsteady aerodynamics ofslender wings and aircraf t undergoing large amplitude maneuvers

Abstract: Aircraft that maneuver through large angles ofattack will experience large regions offlow separation over the wing and fuselage. The separated flow field is characterized by unsteadiness and strong vortical flow structures that can interact with various components ofthe aircraf t. These complicated flow interactions are the primary cause ofmost flight dynamic instabilities, airload nonlinearities and flow field time lags. The aerodynamic and the vortical flow structure over simple delta wings undergoing either a pitching or rolling motion is presented. This article reviews experimental information on the flow structure over delta wings and complete aircraft configurations. First, the flow structure of leading-edge vortices and their influence on delta wing aerodynamics for stationary models is presented. This is followed by a discussion of the effect of large amplitude motion on the vortex structure and aerodynamic characteristic ofpitching and rolling delta wings. The relationship between the flow structure and the unsteady airloads is reviewed. The unsteady motion ofthe delta wing results in a modification ofthe flow field. Delays in flow separation, vortex formation, vortex position and the onset of vortex breakdown are all affected by the model motion. These flow changes cause a corresponding modification in the aerodynamic loads. Data is presented which shows the importance offlow field hysteresis in either vortex position or breakdown and the influence on the aerodynamic characteristics ofa maneuvering delta wing. The free-to-roll motion of a double-delta wing is also presented. The complicated flow structure over a double-delta wing gives rise to damped, chaotic and wing rock motions as the angle ofattack is increased. The concept ofa critical state is discussed and it is shown that crossing a critical state produces large transients in the dynamic airloads. Next, several aircraft configurations are examined to show the importance of unsteady aerodynamics on the flight dynamics ofaircraf t maneuvering at large angles ofattack. The rolling characteristics ofthe F-18 and X-31 configurations are examined. The influence ofthe vortical flow structure on the rolling motion is established. Finally, a briefdiscussion ofnonlinear aerodynamic modeling is presented. The importance ofcritical states and the transient aerodynamics associated with crossing a critical state are examined. r 2003 Elsevier Science Ltd. All rights reserved.

On aerodynamic modelling of an insect–like flapping wing in hover for micro air vehicles

Abstract: This theoretical paper discusses recent advances in the fluid dynamics of insect and micro air vehicle (MAV) flight and considers theoretical analyses necessary for their future development. The main purpose is to propose a new conceptual framework and, within this framework, two analytic approaches to aerodynamic modelling of an insect–like flapping wing in hover in the context of MAVs. The motion involved is periodic and is composed of two half–cycles (downstroke and upstroke) which, in hover, are mirror images of each other. The downstroke begins with the wing in the uppermost and rearmost position and then sweeps forward while pitching up and plunging down. At the end of the half–cycle, the wing flips, so that the leading edge points backwards and the wing9s lower surface becomes its upper side. The upstroke then follows by mirroring the downstroke kinematics and executing them in the opposite direction. Phenomenologically, the interpretation of the flow dynamics involved, and adopted here, is based on recent experimental evidence obtained by biologists from insect flight and related mechanical models. It is assumed that the flow is incompressible, has low Reynolds number and is laminar, and that two factors dominate: (i) forces generated by the bound leading–edge vortex, which models flow separation; and (ii) forces due to the attached part of the flow generated by the periodic pitching, plunging and sweeping. The first of these resembles the analogous phenomenon observed on sharp–edged delta wings and is treated as such. The second contribution is similar to the unsteady aerodynamics of attached flow on helicopter rotor blades and is interpreted accordingly. Theoretically, the fluid dynamic description is based on: (i) the superposition of the unsteady contributions of wing pitching, plunging and sweeping; and (ii) adding corrections due to the bound leading–edge vortex and wake distortion. Viscosity is accounted for indirectly by imposing the Kutta condition on the trailing edge and including the influence of the vortical structure on the leading edge. Mathematically, two analytic approaches are proposed. The first derives all the quantities of interest from the notion of circulation and leads to tractable integral equations. This is an application of the von Karman–Sears unsteady wing theory and its nonlinear extensions due to McCune and Tavares; the latter can account for the bound leading–edge vortex and wake distortion. The second approach uses the velocity potential as the central concept and leads to relatively simple ordinary differential equations. It is a combination of two techniques: (i) unsteady aerodynamic modelling of attached flow on helicopter rotor blades; and (ii) Polhamus9s leadingedge suction analogy. The first of these involves both frequency–domain (Theodorsen style) and time–domain (indicial) methods, including the effects of wing sweeping and returning wake. The second is a nonlinear correction accounting for the bound leading–edge vortex. Connections of the proposed framework with control engineering and aeroelasticity are pointed out.

Insect-Based Hover-Capable Flapping Wings for Micro Air Vehicles: Experiments and Analysis

Abstract: This paper addresses the aerodynamics of insect-based, biomimetic, flapping wings in hover. An experimental apparatus, with a biomimetic flapping mechanism, was used to measure the thrust generated by a number of wing designs at different wing pitch settings. To quantify the large inertial loads acting on the wings, vacuum chamber tests were conducted. Results were obtained for several high-frequency tests conducted on lightweight aluminum and composite wings. The wing mass was found to have a significant influence on the maximum frequency of the mechanism because of a high inertial power requirement. All the wings tested showed a decrease in thrust at high frequencies. In contrast, for a wing held at 90-deg pitch angle, flapping in a horizontal stroke plane with passive pitching caused by aerodynamic and inertial forces, the thrust was found to be larger. To study the effect of passive pitching, the biomimetic flapping mechanism was modified with a passive torsion spring on the flapping shaft. Results of some tests conducted with different wings and different torsion spring stiffnesses are shown. A soft torsion spring led to a greater range of pitch variation and produced more thrust at slightly lower power than with the stiff torsion spring. The lightweight and highly flexible wings used in this study had significant aeroelastic effects which need to be investigated. A finite element based structural analysis of the wing is described, along with an unsteady aerodynamic analysis based on indicial functions. The analysis was validated with experimental data available in literature, and also with experimental tests conducted on the biomimetic flapping-pitching mechanism. Results for both elastic and rigid wing analyses are compared with the thrust measured on the biomimetic flapping-pitching mechanism.