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Van Dam, C. P.

Publications and source records attributed to Van Dam, C. P..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Two-dimensional computational analysis of a transport high-lift system and a comparison with flight-test results

Two currently available coupled inviscid/viscous multielement computational codes, including a relatively simple panel method and an Euler method, are used to analyze a high-lift system. The results are compared with two-dimensional wind-tunnel test results and then with the three-dimensional flight-test results obtained from the NASA Langley Transport Systems Research Vehicle five-element high-lift wing section. Comparisons were also made between the panel method, the Euler method, and flight data for two high-lift configurations, one representing a take-off configuration and the other an approach configuration. For the take-off configuration, both codes agreed reasonably well with experimental data, but both codes were found to overpredict the flap upper-surface pressures for the approach configuration.

Hardin, Jay D.↗
NASA NTRS1993

Leading-edge transition and relaminarization phenomena on a subsonic high-lift system

Boundary-layer transition and relaminarization may have a critical effect on the flow development about multielement high-lift systems of subsonic transport aircraft with swept wings. The purpose of this paper is a study of transition phenomena in the leading-edge region of the various elements of a high-lift system. The flow phenomena studied include transition of the attachment-line flow, relaminarization, and crossflow instability. The calculations are based on pressure distributions measured in flight on the NASA Transport Systems Research Vehicle (Boeing 737-100) at a wing station where the flow approximated infinite swept wing conditions. The results indicate that significant regions of laminar flow can exist on all flap elements in flight. In future flight experiments the extent of these regions will be measured, and the transition mechanisms and the effect of laminar flow on the high-lift characteristics of the multi-element system will be further explored.

Van Dam, C. P.↗
NASA NTRS1993

Shape optimization for aerodynamic efficiency and low observability

Field methods based on the finite-difference approximations of the time-domain Maxwell's equations and the potential-flow equation have been developed to solve the multidisciplinary problem of airfoil shaping for aerodynamic efficiency and low radar cross section (RCS). A parametric study and an optimization study employing the two analysis methods are presented to illustrate their combined capabilities. The parametric study shows that for frontal radar illumination, the RCS of an airfoil is independent of the chordwise location of maximum thickness but depends strongly on the maximum thickness, leading-edge radius, and leadingedge shape. In addition, this study shows that the RCS of an airfoil can be reduced without significant effects on its transonic aerodynamic efficiency by reducing the leading-edge radius and/or modifying the shape of the leading edge. The optimization study involves the minimization of wave drag for a non-lifting, symmetrical airfoil with constraints on the airfoil maximum thickness and monostatic RCS. This optimization study shows that the two analysis methods can be used effectively to design aerodynamically efficient airfoils with certain desired RCS characteristics.

Vinh, Hoang↗
NASA NTRS1993

Accurate drag prediction: A prerequisite for drag reduction research

An improved technique for drag prediction based on the analysis of wake flows is presented and demonstrated. The technique is demonstrated using three-dimensional flow field solutions obtained with several Euler codes. The flow field solutions are obtained for several wing configurations at both lifting and nonlifting conditions for a range of speeds. At subsonic speeds, the induced-drag prediction is shown to be more accurate (and virtually independent of numerical viscosity levels in the Euler flow field solutions) than the prediction obtained by surface integration. At transonic speeds, a separate wave-drag prediction procedure allows the decomposition of the total inviscid drag into wave drag and induced drag. Preliminary results indicate that the drag-prediction technique in a slightly revised form may be applicable to predict induced drag and wave drag at supersonic speeds.

Wong, Kent J.↗
NASA NTRS1992

Finite-difference algorithms for the time-domain Maxwell's equations - A numerical approach to RCS analysis

The applications of two CFD-based finite-difference methods to computational electromagnetics are investigated. In the first method, the time-domain Maxwell's equations are solved using the explicit Lax-Wendroff scheme and in the second method, the second-order wave equations satisfying the Maxwell's equations are solved using the implicit Crank-Nicolson scheme. The governing equations are transformed to a generalized curvilinear coordinate system and solved on a body-conforming mesh using the scattered-field formulation. The induced surface current and the bistatic radar cross section are computed and the results are validated for several two-dimensional test cases involving perfectly-conducting scatterers submerged in transverse-magnetic plane waves.

Vinh, Hoang↗
NASA NTRS1992

Prediction of drag at subsonic and transonic speeds using Euler methods

A technique for the evaluation of aerodynamic drag from flowfield solutions based on the Euler equations is discussed. The technique is limited to steady attached flows around three-dimensional configurations in the absence of active systems such as surface blowing/suction and propulsion. It allows the decomposition of the total drag into induced drag and wave drag and, consequently, it provides more information on the drag sources than the conventional surface-pressure integration technique. The induced drag is obtained from the integration of the kinetic energy (per unit distance) of the trailing vortex system on a wake plane and the wave drag is obtained from the integration of the entropy production on a plane just downstream of the shocks. The drag-evaluation technique is applied to three-dimensional flowfield solutions for the ONERA M6 wing as well as an aspect-ratio-7 wing with an elliptic spanwise chord distribution and an NACA-0012 section shape. Comparisons between the drag obtained with the present technique and the drag based on the integration of surface pressures are presented for two Euler codes.

Nikfetrat, K.↗
NASA NTRS1992

Practical design optimization of wing/body configurations using the Euler equations

The development of a practical method for the aerodynamic design of isolated wing and wing/body configurations is achieved through the coupling of existing computational fluid dynamics (CFD) analysis codes and a quasi-Newton numerical optimization method. The direct design method is generalized to treat three-dimensional aerodynamic optimization problems subject to inviscid, rotational, compressible flow conditions imposed by the Euler equations. The method couples either the FLO57 or the TEAM flow solver with a modified version of the QNMDIF numerical optimization algorithm. The method is applied, but is not limited, to supersonic design problems. A case study is presented illustrating the method's effectiveness in maximizing the lift-to-drag ratio, subject to a variety of constraints, of selected supersonic configurations at cruise conditions.

Reuther, J.↗
NASA NTRS1991

Wing design code using three-dimensional Euler equations and optimization

This paper describes a new wing design code which is based on the Euler equations and a constrained numerical optimization technique. The geometry modification is based on a set of fundamental modes define on the unit interval. A design example involving a high speed civil transport wing is presented to demonstrate the usefulness of the design code. It is shown that the use of an Euler solver in the direct numerical optimization procedures is affordable on the current generation of supercomputers.

Chang, I-Chung↗
NASA NTRS1991

Drag calculations of wings using Euler methods

Several techniques for the calculation of drag using Euler-equation formulations are discussed and compared. Surface-pressure integration (a nearfield technique) as well as two different farfield calculation techniques are described and applied to three-dimensional flow-field solutions for an aspect-ratio-7 wing with attached flow. The present calculations are limited to steady, low-Mach-number flows around three-dimensional configurations in the absence of active systems such as surface blowing/suction and propulsion. Although the main focus of the paper is the calculation of aerodynamic drag, the calculation of aerodynamic lift is also briefly discussed. Three Euler methods are used to obtain the flowfield solutions. The farfield technique based on the evaluation of a wake-integral appears to provide the most consistent and accurate drag predictions.

Van Dam, C. P.↗
NASA NTRS1990

Subsonic and transonic low-Reynolds-number airfoils with reduced pitching moments

A subsonic and a transonic airfoil are presented for application in a high-altitude long-endurance aircraft and a very-high-altitude aircraft, respectively. The subsonic airfoil is designed for a lift coefficient c(l) = 1.4 at a chord Reynolds number Re = 700,000 and a very low Mach number. The transonic airfoil is designed for c(l) = 1.0 at Re = 500,000 and a transonic Mach number M = 0.7. Both airfoils are developed to perform as well or better than previously designed airfoils. However, the present airfoils are developed for a constrained pitching moment to reduce aircraft trim drag and to relieve, to some extent, the torsional loads in the typically high-aspect-ratio wings. The beneficial effects of a cruise flap and of boundary-layer transition control on the off-design performance characteristics are illustrated.

Van Dam, C. P.↗
NASA NTRS1990

Parametric analysis of swept-wing geometry with sheared wing tips

A computational parameter study is presented of potential reductions in induced drag and increases in lateral-directional stability due to sheared wing tips attached to an untwisted wing of moderate sweep and aspect ratio. Sheared tips are swept and tapered wing-tip devices mounted in the plane of the wing. The induced-drag results are obtained using an inviscid, incompressible surface-panel method that models the nonlinear effects due to the deflected and rolled-up wake behind the lifting surface. The induced-drag results with planar sheared tips are compared to straight-tapered tip extensions and nonplanar winglet geometries. The lateral-directional static-stability characteristics of the wing with sheared tips are estimated using a quasi-vortex-lattice method. For certain combinations of sheared-tip sweep and taper, both the induced efficiency of the wing and the relevant static-stability derivatives are predicted to increase compared to the wing with a straight-tapered tip modification.

Fremaux, C. M.↗
NASA NTRS1990

Wind-tunnel investigation on the effect of a crescent planform on drag

Lift and drag forces were compared for elliptic and crescent wing models at cruise and climb conditions in the NASA/Langley 14 x 22-ft subsonic tunnel. The force measurements were obtained for an angle-of-attack range from -3 to 10 deg at a Reynolds number of about 1.7 million. The results indicate that for attached flow conditions, the crescent wing with its highly swept tips generates less lift-dependent drag than the elliptic wing for given lift force, wing span, and freestream conditions. The drag reduction is thought to be the result of the favorable influence of trailing wake deformations on the pressure distribution of the highly swept outboard region of the crescent wing.

Van Dam, C. P.↗
NASA NTRS1989

Wind-tunnel investigations of wings with serrated sharp trailing edges

Exploratory wind-tunnel force measurements are presented for two wing geometries with small-scale planar and nonplanar serrated trailing-edge devices (chord-Reynolds numbers ranged from 1.0 to 3.7 million). The planar serrated trailing-edge extensions reduced the drag at conditions when trailing-edge separation occurred at low angles of attack. The introduction of serrations reduced or eliminated the drag penalty, due to the small (1-2 percent of the chord length) nonplanar trailing-edge flaps, while maintaining the effects of increase in camber. The presence of streamwise vortices immediately downstream of the serrated trailing edges is believed to have favorably affected the boundary-layer flow approaching the trailing edge and the near-wake development, resulting in reduced pressure (form) drag.

Vijgen, P. M. H. W.↗
NASA NTRS1989

Sheared wing-tip aerodynamics - Wind-tunnel and computational investigation

Computational and experimental performance benefits are presented for a high-aspect-ratio unswept wing configuration with sheared tips. The sheared tip is a highly swept and highly tapered surface located in the same plane as the inboard wing panel to which it is attached. The compuational results were obtained with an inviscid surface panel method that models the nonlinear influence of the trailing wake. Both wind-tunnel and calculated results were obtained for a 12-ft span wing model with various wing-tip configurations. The computational and experimental data are in fair agreement and demonstrate that sheared wing tips can reduce induced drag at cruise and climb lift coefficients. The drag reduction is the result of wake deformation effects and changes in spanwise load distribution. Wind-tunnel measured longitudinal and lateral directional stability characteristics are also presented for the various wing-tip layouts.

Vijgen, P. M. H. W.↗