On management and control of turbulent shear flows

Relative performance of several passive and active methods for controlling two-dimensional turbulent separated flow associated with a curved backward-facing ramp were investigated at low speeds. Surface static pressure measurement and oil flow visualization results indicate that submerged vortex generators, vortex generator jets, elongated arches at +-alpha, and large-eddy breakup devices at +-alpha placed near the baseline separation location reduce flow separation and increase pressure recovery. Spanwise cylinders reduce flow separation but decrease pressure recovery downstream. Arches with alpha = 0 deg, Helmholtz resonators, and Viets' fluidic flappers examined so far have no significant effect in reducing separation. Wall cooling computation indicates that separation delay on a partially cooled ramp is nearly the same as on a fully-cooled ramp while minimizing the frictional drag increase associated with the wall cooling process.

Investigation of several passive and active methods for turbulent flow separation control

Several passive separation control techniques for controlling moderate two-dimensional turbulent flow separation over a backward-facing ramp are studied. Small transverse and swept grooves, passive porous surfaces, large longitudinal grooves, and vortex generators were among the techniques used. It was found that, unlike the transverse and longitudinal grooves of an equivalent size, the 45-deg swept-groove configurations tested tended to enhance separation.

Turbulent flow separation control through passive techniques

Maneuver load alleviation, gust load alleviation, and natural laminar flow are integrated into aircraft conceptual design. The concurrent design of the aircraft and its active load alleviation systems can yield significant gains. The simultaneous application of maneuver load alleviation and gust load alleviation to a short-haul aircraft leads to an 11% reduction in fuel burn and 7% reduction in direct operating cost. These savings are diminished if maneuver load alleviation and gust load alleviation are applied independently. The synergy between active load control and natural laminar flow is also explored. It is possible to invest some of the weight savings from load alleviation to achieve extensive laminar flow. The combination of load alleviation and natural laminar flow increases the fuel and cost savings to upwards of 18 and 11%, respectively. It is concluded that load alleviation can shift the transonic transport optimum toward low-sweep, natural laminar flow wings. Sensitivity studies finally demon...

Aircraft Design with Active Load Alleviation and Natural Laminar Flow

The focus of the research was to investigate the fundamental aerodynamics of the base flow of a tractor trailer that would prove useful in fluid flow management. Initially, industry design needs and constraints were defined. This was followed by an evaluation of state-of-the-art Navier-Stokes based computational fluid dynamics tools. Analytical methods were then used in combination with computational tools in a design process. Several geometries were tested at 1:8 scale in a low speed wind tunnel. In addition to the baseline geometry, base add-on devices of the class of ogival boattails and slants were analyzed.

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Aerodynamics overview of the ground transportation systems (GTS) project for heavy vehicle drag reduction

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

R. S. Lee

Papers

Optimum tail shapes for bodies of revolution