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Nixon, D.

Publications and source records attributed to Nixon, D..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Prediction of unsteady transonic flow around missile configurations

This paper describes the preliminary development of a method for predicting the unsteady transonic flow around missiles at transonic and supersonic speeds, with the final goal of developing a computer code for use in aeroelastic calculations or during maneuvers. The basic equations derived for this method are an extension of those derived by Klopfer and Nixon (1989) for steady flow and are a subset of the Euler equations. In this approach, the five Euler equations are reduced to an equation similar to the three-dimensional unsteady potential equation, and a two-dimensional Poisson equation. In addition, one of the equations in this method is almost identical to the potential equation for which there are well tested computer codes, allowing the development of a prediction method based in part on proved technology.

Nixon, D.↗
NASA NTRS1982

Unsteady Transonic Small Disturbance theory with strong shock waves

Transonic Small Disturbance (TSD) theory is modified to yield steady and unsteady solutions in the case of strong shock waves (where the local Mach number ahead of the shock exceeds 1.3). The modification consists of an additional adjustable nonlinear term which allows the exact Rankine-Hugoniot shock jump relation to be satisfied at all times. The modified TSD theory is applied to steady and unsteady oscillatory transonic flows, and yields results which are in good agreement with solutions of the unsteady Euler equations, and which compare favorably with solutions of the full potential equation when shock waves are weak.

Kerlick, G. D.↗
NASA NTRS1982

Transonic aerodynamics; Transonic Perspective Symposium, Moffett Field, CA, February 18-20, 1981, Technical Papers

After an historical account of the development of transonic aerodynamics before 1940 and in the period 1945-1975, attention is given to the design for cruise performance efficiency of commercial transport aircraft, with emphasis on transonic wing design, the practical aerodynamic problems of military aircraft, with emphasis on store carriage and separation, experimental testing in transonic wind tunnels capable of Reynolds number simulation and aerodynamic flow visualization, and such mathematical techniques as potential equation methods for flow prediction and Reynolds-averaged Navier-Stokes computations of transonic flows. Also considered are transonic design using computational aerodynamics, the application of computation methods to transonic wing design, computational experience with advanced tactical aircraft, the evaluation of full potential flow methods, and the application of a shock-turbulent boundary layer interaction theory to transonic flowfield analysis.

Nixon, D.↗
NASA NTRS1980

Unsteady transonic small disturbance theory with strong shock waves

A theory to correct the transonic small disturbance (TSD) equation to treat strong shock waves in unsteady flow is developed. The technique involves the addition of higher order terms, which are formally of negligible magnitude, to the low frequency TSD equation. These terms are then chosen such that any shock waves in the flow have strengths approximately equal to the appropriate Rankine-Hugoniot shock strength. Two correcting approaches are investigated. The first is to derive a correction for the mean steady flow and then simply use this corrected form for oscillatory flows. The second is to derive a correction for both steady and oscillatory parts of the flow. This second development is the most satisfactory and comparisons of the present results with Euler equation results are generally favorable, particularly regarding shock location, although there are some discrepancies in the pressure distribution in the leading edge region.

Kerlick, G. D.↗
NASA NTRS1979

A prototype DSN X-S band feed: DSS 13 application

A prototype X-S band horn feed for future use at various DSN sites, dealing with the testing of the final fabricated feed at DSS 13 are discussed. Measured feedhorn patterns are presented, and efficiencies calculated. Preliminary results of system noise temperature and 26-m antenna system gain measurements are presented. Some measurements leading to an improved second generation feed are described. The results of the field measurements indicate that this horn will perform as originally specified and required. The tests for the second generation feed have indicated the potential cause of minor X-band moding.

Williams, W.↗
NASA NTRS1979

Design of transonic airfoil sections using a similarity theory

In the present paper, it is shown that numerical optimization is a powerful tool for designing transonic wings and airfoils. Nixon's (1978) similarity theory is extended to cover design optimization problems. Some ground rules for designing shock-free airfoils are proposed and their application is demonstrated by examples. Advantages which accrue from integrating similarity theory into the numerical optimization procedure are noted.

Nixon, D.↗
NASA NTRS1978

Design of transonic airfoil sections using a similarity theory

A study of the available methods for transonic airfoil and wing design indicates that the most powerful technique is the numerical optimization procedure. However, the computer time for this method is relatively large because of the amount of computation required in the searches during optimization. The optimization method requires that base and calibration solutions be computed to determine a minimum drag direction. The design space is then computationally searched in this direction; it is these searches that dominate the computation time. A recent similarity theory allows certain transonic flows to be calculated rapidly from the base and calibration solutions. In this paper the application of the similarity theory to design problems is examined with the object of at least partially eliminating the costly searches of the design optimization method. An example of an airfoil design is presented.

Nixon, D.↗
NASA NTRS1978

Direct numerical solution of the transonic perturbation integral equation for lifting and nonlifting airfoils

The linear transonic perturbation integral equation previously derived for nonlifting airfoils is formulated for lifting cases. In order to treat shock wave motions, a strained coordinate system is used in which the shock location is invariant. The tangency boundary conditions are either formulated using the thin airfoil approximation or by using the analytic continuation concept. A direct numerical solution to this equation is derived in contrast to the iterative scheme initially used, and results of both lifting and nonlifting examples indicate that the method is satisfactory.

Nixon, D.↗
NASA NTRS1978

Perturbations in two- and three-dimensional transonic flows

The difficulty of treating the perturbation of transonic flow, during which shock waves change position, can be overcome by using a distorted coordinate system in which the locations of all shock waves do not change; the distortion is found as part of the solution. This device leads to a relation that allows a range of flows, with differing shock locations, to be related algebraically to two known 'calibration' flows. Results for flows around finite wings, including those with multiple, intersecting shock waves, are presented. A typical computing time for such examples is 0.3 sec on a CDC 7600 computer.

Nixon, D.↗
NASA NTRS1978

Notes on the transonic indicial method

The indicial method for calculating flutter derivatives for two-dimensional airfoils at transonic speeds is discussed, with particular attention given to the effect of a moving shock on the flow variables in the indicial method. An expression for the pressure coefficient is developed on the basis of an explicit treatment of the shock motion; the pressure distribution may then be calculated for general oscillations through use of the indicial method. Explicit inclusion of the shock motion is not necessary if only the lift and pitching moment coefficients are desired.

Nixon, D.↗
NASA NTRS1978

Calculation of unsteady transonic flows using the integral equation method

The basic integral equations for a harmonically oscillating airfoil in a transonic flow with shock waves are derived; the reduced frequency is assumed to be small. The problems associated with shock wave motion are treated using a strained coordinate system. The integral equation is linear and consists of both line integrals and surface integrals over the flow field which are evaluated by quadrature. This leads to a set of linear algebraic equations that can be solved directly. The shock motion is obtained explicitly by enforcing the condition that the flow is continuous except at a shock wave. Results obtained for both lifting and nonlifting oscillatory flows agree satisfactorily with other accurate results.

Nixon, D.↗
NASA NTRS1977

Perturbation of a discontinuous transonic flow

The main difficulty in perturbing a discontinuous transonic flow is in the representation of the shift in the location of the discontinuity (shock wave). Herein presented is a method of overcoming this difficulty by using a distorted airfoil as the initial case rather than the real physical airfoil; the distortion is chosen such that the shock location is unchanged by the perturbation. The distorted airfoil is obtained by the use of a strained coordinate system. A direct consequence of the theory is the derivation of an algebraic similarity relation between related airfoils with shock waves at differing locations. Results for simple examples are shown.

Nixon, D.↗
NASA NTRS1976

Calculation of transonic flows using an extended integral equation method

An extended integral equation method for transonic flows is developed. In the extended integral equation method velocities in the flow field are calculated in addition to values on the aerofoil surface, in contrast with the less accurate 'standard' integral equation method in which only surface velocities are calculated. The results obtained for aerofoils in subcritical flow and in supercritical flow when shock waves are present compare satisfactorily with the results of recent finite difference methods.

Nixon, D.↗
NASA NTRS1974

A computer simulation of Skylab dynamics and attitude control for performance verification and operational support

A simulation of the Skylab attitude and pointing control system (APCS) is outlined and discussed. Implementation is via a large hybrid computer and includes those factors affecting system momentum management, propellant consumption, and overall vehicle performance. The important features of the flight system are discussed; the mathematical models necessary for this treatment are outlined; and the decisions involved in implementation are discussed. A brief summary of the goals and capabilities of this tool is also included.

Buchanan, H.↗