L. H. Jorgensen

Bio: L. H. Jorgensen is an academic researcher from Ames Research Center. The author has contributed to research in topics: Aerodynamic force & Aerodynamics. The author has an hindex of 1, co-authored 1 publications receiving 85 citations.

Prediction of static aerodynamic characteristics for slender bodies alone and with lifting surfaces to very high angles of attack

Abstract: An engineering-type method is presented for computing normal-force and pitching-moment coefficients for slender bodies of circular and noncircular cross section alone and with lifting surfaces. In this method, a semi-empirical term representing viscous-separation crossflow is added to a term representing potential-theory crossflow. For many bodies of revolution, computed aerodynamic characteristics are shown to agree with measured results for investigated free-stream Mach numbers from 0.6 to 2.9. The angles of attack extend from 0 deg to 180 deg for M = 2.9 from 0 deg to 60 deg for M = 0.6 to 2.0. For several bodies of elliptic cross section, measured results are also predicted reasonably well over the investigated Mach number range from 0.6 to 2.0 and at angles of attack from 0 deg to 60 deg. As for the bodies of revolution, the predictions are best for supersonic Mach numbers. For body-wing and body-wing-tail configurations with wings of aspect ratios 3 and 4, measured normal-force coefficients and centers are predicted reasonably well at the upper test Mach number of 2.0. Vapor-screen and oil-flow pictures are shown for many body, body-wing and body-wing-tail configurations. When spearation and vortex patterns are asymmetric, undesirable side forces are measured for the models even at zero sideslip angle. Generally, the side-force coefficients decrease or vanish with the following: increase in Mach number, decrease in nose fineness ratio, change from sharp to blunt nose, and flattening of body cross section (particularly the body nose).

Steady and Unsteady Vortex-Induced Asymmetric Loads on Slender Vehicles

Abstract: body length forebody length forward of rotation center (Fig. 8) nose length = rolling moment, coefficient C, = £/ (p* U^ /2)Sb vortex wake wave length Mach number pitching moment, coefficient Cm=Mp/(PooUl/2)Sc yawing moment, coefficient Cn=n/(p00 U00/2)Sc = normal force, coefficient CN=N/ (p^ C/i/2)S = nose tip roll rate = pitch rate Reynolds number based on dmax and freestream conditions; usually Re = Rd Reynolds number, Rd = U^d/v^ reference area, S = ird /4 reference area ( = projected wing area) time velocity axial body-fixed coordinate (distance from apex) side force, coefficient CY=Y/(PooUx /2)S angle of attack da/df, C^ = d C m / d j > ' l 0 / U ( X ) sideslip angle rotation of plane of symmetry of forebody vortices (Fig. 8) cone half-angle 6A = apex half-angle p = air density = roll angle 5 = three-dimensional separation angle (Fig. 15) a' = total angle of inclination (Fig. 8) v — kinematic viscosity oj = angular rate

Investigation of Normal Force and Moment Coefficients for an AUV at Nonlinear Angle of Attack and Sideslip Range

Abstract: This paper presents a comparative study of computational fluid dynamics (CFD) and analytical and semiempirical (ASE) methods applied to the prediction of the normal force and moment coefficients of an autonomous underwater vehicle (AUV). Both methods are applied to the bare hull of the vehicle and to the body-hydroplane combination. The results are validated through experiments in a towing tank. It is shown that the CFD approach allows for a good prediction of the coefficients over the range of angles of attack considered. In contrast with the traditional ASE formulations used in naval and aircraft fields, an improved methodology is introduced that takes advantage of the qualitative information obtained from CFD flow visualizations.

Flow-separation patterns on symmetric forebodies

Abstract: Flow-visualization studies of ogival, parabolic, and conical forebodies were made in a comprehensive investigation of the various types of flow patterns. Schlieren, vapor-screen, oil-flow, and sublimation flow-visualization tests were conducted over an angle-of-attack range from 0 deg. to 88 deg., over a Reynolds-number range from 0.3X10(6) to 2.0X10(6) (based on base diameter), and over a Mach number range from 0.1 to 2. The principal effects of angle of attack, Reynolds number, and Mach number on the occurrence of vortices, the position of vortex shedding, the principal surface-flow-separation patterns, the magnitude of surface-flow angles, and the extent of laminar and turbulent flow for symmetric, asymmetric, and wake-like flow-separation regimes are presented. It was found that the two-dimensional cylinder analogy was helpful in a qualitative sense in analyzing both the surface-flow patterns and the external flow field. The oil-flow studies showed three types of primary separation patterns at the higher Reynolds numbers owing to the influence of boundary-layer transition. The effect of angle of attack and Reynolds number is to change the axial location of the onset and extent of the primary transitional and turbulent separation regions. Crossflow inflectional-instability vortices were observed on the windward surface at angles of attack from 5 deg. to 55 deg. Their effect is to promote early transition. At low angles of attack, near 10 deg., an unexpected laminar-separation bubble occurs over the forward half of the forebody. At high angles of attack, at which vortex asymmetry occurs, the results support the proposition that the principal cause of vortex asymmetry is the hydrodynamic instability of the inviscid flow field. On the other hand, boundary-layer asymmetries also occur, especially at transitional Reynolds numbers. The position of asymmetric vortex shedding moves forward with increasing angle of attack and with increasing Reynolds number, and moves rearward with increasing Mach number.