Analysis and mitigation of numerical dissipation in inviscid and viscid computation of vortex-dominated flows

The conservative unsteady Euler equations for the flow relative motion in the moving frame of reference are used to solve for the steady and unsteady flows around sharp-edged delta wings. The resulting equations are solved by using an implicit approximately-factored finite volume scheme. Implicit second-order and explicit second- and fourth-order dissipations are added to the scheme. The boundary conditions are explicitly satisfied. The grid is generated by locally using a modified Joukowski transformation in cross flow planes at the grid chord stations. The computational applications cover a steady flow around a delta wing whose results serve as the initial conditions for the unsteady flow around a pitching delta wing about a large angle of attack. The steady results are compared with the experimental data and the periodic solution is achieved within the third cycle of oscillation

Prediction and Control of Asymmetric Vortical Flows Around Slender Bodies Using Navier-Stokes Equations

Steady and unsteady vortex-dominated flows around slender bodies at high angles of attack are solved using the unsteady, compressible Navier-Stokes equations. An implicit upwind, finite-volume scheme is used for the numerical computations. For supersonic flows past pointed bodies, the locally-conical flow assumption has been used. Asymmetric flows past five-degree semiapex cones using the thin-layer Navier-Stokes equations at different angles of attack, freestream Mach numbers, Reynolds numbers, grid fineness, computational domain size, sources of disturbances and cross-section shapes have been studied. The onset of flow asymmetry occurs when the relative incidence of pointed forebodies exceeds certain critical values. At these critical values of relative incidence, asymmetric flow develops irrespective of the sources of disturbances. The results of unsteady asymmetric flows show that periodic vortex shedding exists at larger angles of attack and it is independent of the numerical schemes used. Passive control of steady and unsteady asymmetric vortical flows around cones using vertical fins and side-strakes have also been studied. Side-strikes control of flow asymmetry over a wide range of angles of attack requires shorter strake heights than those of the vertical-fin control and produces higher lift for the same cone. Three-dimensional, incompressible flows past a prolate spheroid and a tangent-ogive cylinder are solved and compared with experimental data for validation of the numerical scheme. Three-dimensional supersonic asymmetric flows around a five degree semiapex angle circular cone at different angles of attack and Reynolds numbers are presented. Flow asymmetry has been obtained using short-duration disturbances. The flow asymmetry becomes stronger as the Reynolds number and angle of attack are increased. The asymmetric solutions show spatial vortex shedding which is qualitatively similar to the temporal vortex shedding of the unsteady locally-conical flow

Aeronautical engineering: A continuing bibliography with indexes (supplement 239)

This bibliography lists 454 reports, articles, and other documents introduced into the NASA scientific and technical information system in April, 1989. Subject coverage includes: design, construction and testing of aircraft and aircraft engines; aircraft components, equipment and systems; ground support systems; and theoretical and applied aspects of aerodynamics and general fluid dynamics

Aeronautical engineering: A cumulative index to a continuing bibliography (supplement 248)

This publication is a cumulative index to the abstracts contained in Supplements 236 through 247 of Aeronautical Engineering: A Continuing Bibliography. The bibliographic series is compiled through the cooperative efforts of the American Institute of Aeronautics and Astronautics (AIAA) and the National Aeronautics and Space Administration (NASA). Seven indexes are included -- subject, personal author, corporate source, foreign technology, contract number, report number and accession number