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Lovell, D.

Publications and source records attributed to Lovell, D..

8 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Entropy and vorticity corrections for transonic flows

Different models for inviscid transonic flows are examined. The common assumptions that the flow is isentropic and irrotational are critically evaluated. Entropy and vorticity correction procedures for potential and stream function formulations are presented, together with the details of the treatment of shocks and wakes, and drag and lift calculations. The non-uniqueness problem of the potential formulation is studied using different artificial viscosity forms. Numerical results are compared with Euler solutions.

Hafez, M.↗
NASA NTRS1986

Two-dimensional transonic wind-tunnel wall interference corrections based on the Euler equations

A procedure for the evaluation of wall interference corrections for two-dimensional models is presented. The Mach number and angle-of-attack corrections require the numerical solution of the Euler equations. Pressure measurements are required near the wind tunnel walls. The correction procedure also requires knowledge of the free-stream Mach number, the model geometry, and the lift force experienced by the model. The residual interference not accounted for by the Mach number and angle-of-attack corrections is estimated.

Rizk, M. H.↗
NASA NTRS1983

Improved relaxation schemes for transonic potential calculations

A block relaxation scheme, grouped in a red-black ordering, is applied to transonic airfoil calculations using body fitted coordinates. The scheme is simple and is easily vectorizable. Detailed comparisons with Approximate Factorization Method (AF2) are presented and it is shown that the improved relaxation scheme is competitive in all cases considered. Transonic results, of engineering accuracy, on an 0-type grid of 149 x 30 points, are ususally obtained within two hundred iterations (approximately 40 seconds on Cyber 175).

Hafez, M.↗
NASA NTRS1983

Entropy and vorticity corrections for transonic flows

Different models for inviscid transonic flows are examined. The common assumptions that the flow is isentropic and irrotational are critically evaluated. Entropy and vorticity correction procedures for potential and stream function formlations are presented together with the details of the treatment of shocks and wakes, and drag and lift calculations. The nonuniqueness problem is studied using different artificial viscosity forms. Numerical results are compared to Euler solutions.

Hafez, M.↗
NASA NTRS1983

Transonic small disturbance calculations including entropy corrections

Murman's fully conservative mixed type finite-difference operators are first modified. A special sonic point operator with an iterative damping term is introduced which helps the convergence and does not affect the spatial conservative differences. Reliable calculations with second order supersonic schemes are obtained using two sonic operators, the regular sonic point operator followed by a first order supersonic scheme. Also, shock point operator is shown to be equivalent to fitting a locally normal shock terminating the supersonic region. The potential calculations are then modified to account for the non-isentropic jump conditions using a simple shock fitting procedure based on Prandtl relation. The entropy increase across the shock is calculated in terms of the Mach number upstream of the shock and the effect of the generated vorticity is estimated via Crocco relation. Different examples are calculated and extensions to the full potential equation are discussed.

Hafez, M.↗
NASA NTRS1982

Transonic wind tunnel wall interference corrections for three-dimensional models

A procedure for the evaluation of wall interference corrections for three-dimensional models is presented. The Mach number and angle-of-attack corrections require the numerical solution of the potential equation about a simplified representation of the experimental model. Pressure measurements are required near the wind tunnel walls. The correction procedure also requires knowledge of the free-stream Mach number, the model angle of attack, and the lift force experienced by the model. The procedure provides an estimate of the accuracy of the correction. For slender configurations at Mach numbers close to one, the Equivalence Rule formulation is adopted to calculate the wall interference effects. Preliminary results are presented for both general and slender-body configurations.

Rizk, M. H.↗
NASA NTRS1981

Numerical solution of transonic stream function equation

The stream function equation, in conservation form, looks similar to the full potential equation and existing methods (e.g. artificial compressibility) can be readily applied. Rotational flows can be calculated once the vorticity (due to shocks or nonuniformity) is evaluated. There are, however, two main difficulties: First, the density is not uniquely determined in terms of the flux (there are two solutions; the subsonic and the supersonic branch with a square root singularity at the sonic point). Methods to overcome this difficulty are studied and results are presented with some remarks on inviscid separation and closed stream lines. Second, the need of two stream functions for three dimensional calculations is briefly discussed.

Hafez, M.↗