NASA Scientific and Technical Aerospace Reports
NASA Scientific and Technical Aerospace Reports
NASA Scientific and Technical Aerospace Reports
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Direct numerical simulation was used to study the formation <strong>and</strong> growth of a hairpin vortex in a flat-plate boundary layer<br />
<strong>and</strong> its later development into a young turbulent spot. Fluid injection through a slit in the wall triggered the initial vortex. The<br />
legs of the vortex were stretched into a hairpin shape as it traveled downstream. Multiple hairpin vortex heads developed<br />
between the stretched legs. New vortices formed beneath the streamwise-elongated vortex legs. The continued development<br />
of additional vortices resulted in the formation of a traveling region of highly disturbed ow with an arrowhead shape similar<br />
to that of a turbulent spot.<br />
Author<br />
Direct Numerical Simulation; Horseshoe Vortices; Turbulence; Mathematical Models<br />
20040112024 <strong>NASA</strong> Glenn Research Center, Clevel<strong>and</strong>, OH, USA<br />
Unsteady Jets in Crossflow<br />
Zaman, K. B. M. Q.; [2004]; 10 pp.; In English; ASME Fluids Engineering Summer Meeting, 11-15 Jul. 2004, Charlotte, NC,<br />
USA<br />
Contract(s)/Grant(s): 781-30-47<br />
Report No.(s): HT-FED2004-56822; No Copyright; Avail: CASI; A02, Hardcopy<br />
The effect of periodic perturbation on jet in cross-flow (JICF) is reviewed. In the first part of the paper, flow visualization<br />
result from several past works are discussed. Beginning with description of the characteristic vortex systems of a JICF it is<br />
shown that specific perturbation techniques work by organizing <strong>and</strong> intensifying specific vortex systems. Oscillatory blowing<br />
works primarily through an organization of the shear layer vortices. In the second part of the paper, results of an ongoing<br />
experiment involving another mechanical perturbation technique are discussed. It involves two tabs at the orifice exit whose<br />
asymmetry in placement is reversed periodically. It directly modulates the counter-rotating vortex pair (CVP). Effects of the<br />
perturbation for an array of three adjacent orifices are exploded. The flowfield data show an improvement in mixing compared<br />
to the unperturbed case.<br />
Author<br />
Unsteady Flow; Flow Visualization; Vortices; Orifices; Flow Distribution<br />
20040112026 <strong>NASA</strong> Langley Research Center, Hampton, VA, USA<br />
Direct Simulation of Evolution <strong>and</strong> Control of Three-Dimensional Instabilities in Attachment-Line Boundary Layers<br />
Joslin, Ronald D.; [1995]; 46 pp.; In English; Copyright; Avail: CASI; A03, Hardcopy<br />
The spatial evolution of three-dimensional disturbances in an attachment-line boundary layer is computed by direct<br />
numerical simulation of the unsteady, incompressible Navier-Stokes equations. Disturbances are introduced into the boundary<br />
layer by harmonic sources that involve unsteady suction <strong>and</strong> blowing through the wall. Various harmonic- source generators<br />
are implemented on or near the attachment line, <strong>and</strong> the disturbance evolutions are compared. Previous two-dimensional<br />
simulation results <strong>and</strong> nonparallel theory are compared with the present results. The three-dimensional simulation results for<br />
disturbances with quasi-two-dimensional features indicate growth rates of only a few percent larger than pure two-dimensional<br />
results; however, the results are close enough to enable the use of the more computationally efficient, two-dimensional<br />
approach. However, true three-dimensional disturbances are more likely in practice <strong>and</strong> are more stable than two-dimensional<br />
disturbances. Disturbances generated off (but near) the attachment line spread both away from <strong>and</strong> toward the attachment line<br />
as they evolve. The evolution pattern is comparable to wave packets in at-plate boundary-layer flows. Suction stabilizes the<br />
quasi-two-dimensional attachment-line instabilities, <strong>and</strong> blowing destabilizes these instabilities; these results qualitatively<br />
agree with the theory. Furthermore, suction stabilizes the disturbances that develop off the attachment line. Clearly,<br />
disturbances that are generated near the attachment line can supply energy to attachment-line instabilities, but suction can be<br />
used to stabilize these instabilities.<br />
Author<br />
Boundary Layer Stability; Direct Numerical Simulation; Three Dimensional Flow; Leading Edges<br />
20040112027 <strong>NASA</strong> Langley Research Center, Hampton, VA, USA<br />
Simulation of Synthetic Jets in Quiescent Air Using Unsteady Reynolds Averaged Navier-Stokes Equations<br />
Vatsa, Veer N.; Turkel, Eli L.; [2004]; 13 pp.; In English; 22nd AIAA Applied Aerodynamics Conference <strong>and</strong> Exhibit, 16-19<br />
Aug. 2004, Providence, RI, USA<br />
Contract(s)/Grant(s): 762-45-MC<br />
Report No.(s): AIAA Paper 2004-4967; No Copyright; Avail: CASI; A03, Hardcopy<br />
We report research experience in applying an Unsteady Reynolds-Averaged Navier-Stokes (URANS) solver for the<br />
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