Freestream

About: Freestream is a research topic. Over the lifetime, 3428 publications have been published within this topic receiving 56147 citations.

Influence of numerical dissipation in computing supersonic vortex-dominated flows

Abstract: Steady supersonic vortex-dominated flows are solved using the unsteady Euler equations for conical and three-dimensional flows around sharp- and round-edged delta wings. The computational method is a finite-volume scheme which uses a four-stage Runge-Kutta time stepping with explicit second- and fourth-order dissipation terms. The grid is generated by a modified Joukowski transformation. The steady flow solution is obtained through time-stepping with initial conditions corresponding to the freestream conditions, and the bow shock is captured as a part of the solution. The scheme is applied to flat-plate and elliptic-section wings with a leading edge sweep of 70 deg at an angle of attack of 10 deg and a freestream Mach number of 2.0. Three grid sizes of 29 x 39, 65 x 65 and 100 x 100 have been used. The results for sharp-edged wings show that they are consistent with all grid sizes and variation of the artificial viscosity coefficients. The results for round-edged wings show that separated and attached flow solutions can be obtained by varying the artificial viscosity coefficients. They also show that the solutions are independent of the way time stepping is done. Local time-stepping and global minimum time-steeping produce same solutions.

Design of viscoelastic coatings to reduce turbulent friction drag

Abstract: A method is provided to select appropriate material properties for turbulent friction drag reduction, given a specific body (1), configuration and freestream velocity (2). The method is based on a mathematical description of the balance of energy at the interface between the viscoelastic surface and the moving fluid, and permits determination of the interaction of turbulent boundary layer fluctuations with a viscoelastic layer by solving two subtasks -- i.e., a hydrodynamic problem and an elasticity problem, which are coupled by absorption and compliancy coefficients. Displacement, velocity, and energy transfer boundary conditions on a viscoelastic surface are determined, and a Reynolds stress type turbulence model is modified to account for redistribution of turbulent energy in the near-wall of the boundary layer. The invention permits drag reduction by a coating with specified density, thickness, and complex shear modulus to be predicted for a given body geometry and freestream velocity. For practical applications, viscoelastic coatings may be combined with additional structure, including underlying wedges to minimize edge effects for coatings of finite length, and surface riblets, for stabilization of longitudinal vortices.

Computation of the steady viscous flow over a tri-element 'augmentor wing' airfoil

Abstract: The augmentor wing consists of a main airfoil with a slotted trailing edge for blowing, and two smaller aft airfoils which shroud the jet. This configuration has been modeled for numerical simulation by a novel discretization procedure which generates four separate grids: three surface-oriented airfoil grids and one outer free-stream grid. Grid lines and slopes are continuous across boundaries, so grid overlap at common boundaries provides boundary information without interpolation. A two-dimensional unsteady thin-layer Navier-Stokes code is used to calculate the flow for the no-blowing case at freestream Mach number = 0.7, Re = 12,600.000, and angles-of-incidence = 1.05 deg. Qualitative agreement with experimental data indicates the utility of this procedure in the analysis of multi-element configurations.

Optimum tail shapes for bodies of revolution

Abstract: This paper has n dual purpose: to describe a method of designifig short tails for bodies 01 revolution that sutisfy Stratford's criterion for zero shear at the wall, and to show n few shapes that have been calculated. Stratford's original two-dimensional solution, extended to axisymmetric flow, has been used to implement the prucedure. The method involves simultrmneous solution of the extended Stcatford equation together with the necessary boundary conditions by means of an inverse potential flow program. Tails designed by this procedure are entirely at incipient separmtion (no skin friction); therefore the pressure recovery Is the most rapid possible, making the resultant tail the shortest possible, subject to no separation. The Final result Is a geometry uniquely determined for freestream conditions, the transition point, and of course the basic forebody. The computer program can operate in one of two modes: 1) the forebody geometry can be malntained (except for a small region near the tall juncture) with only the tail shape determined by the method or 2) the forebudy ve1ocity distribution can he malntalned up to the paint of pressure recovery. The forebody geometry wlll then be altered for some distance upstream of the tail juncture. A number of solutions are presented for both of the above modes. Nomenclature A = reference area CIIYOj =drag coefficient based on (vol~me)~ C,,* =drag coefficient based on frontal area C, =pressure coefficient, C, = I - u2 /u&C, = Stratford type pressure coefficient C, = 1 - u2 /ud, I = reference length L = length representative of the length of the body r =radius of body at any point t?, = Reynolds number, U,S/U s =distance along body surface, see Fig. I u =velocity along body outside the boundary layer u, =freestreamvelocity SIA bscripts