Vortex cavities

Figure 11-7 (a) and (b) ventilated gas cavity forms [ a) vortex cavities (b) large cavity] on turbine blades and (c) relative power demand for a gassed Rushton turbine (D/T = 0.4). (Data from Warmoeskerken et al, 1982.)... 

Regimes (1) below minimum dispersion speed (2) vortex cavities, no recirculation (3) vortex cavities with recirculation, (4) flooded, (5) loaded with large cavities (6) large cavities with recirculation. 

Jana, S. C., Metcalfe, G., and Ottino, J. M., Experimental and computational studies of mixing in complex Stokes flow—the vortex mixing flow and the multicellular cavity flow. J. Fluid Mech. 269, 199-246 (1994). 

Figure 11.10 Velocity field in the cavity with the RFM prediction of the vortex center location for a Reynolds number of 100.

Convective mass transport from small cavities is relevant to through-mask electrodeposition and to localized corrosion and has hence received much attention. In localized corrosion, mass transport is important for determination of the local environment inside an active pit. For through-mask deposition, an understanding of mass transport may be important for design of mixing methods or for analysis of measured deposit profiles. The electrodeposition in circular or rectangular cavities formed by a photoresist has been studied by Kondo etal. it was found that the shapes of deposited bumps can be explained by calculations of vortex evolution and penetration flow. 

Vortex and large cavities on upper impellers (multiple impeller systems) develop when FlgFr X 0.2 (Figure 9.30(c))... 

Vortex and large cavities will begin to develop when Fl > 0.03... 

Current numerical efforts are focused on LES benchmarking. Nonreacting jets and jet flames from the Sandia database library will be stndied. Combustion models will initially be based on flamelet concepts, but models which address finite-rate chemistry will also be considered [13, 14]. Flame, emissions, and noise predictions will be compared to experimental data. Predictions of swirl combustor flowfields with comparison to data from the literature and the authors own experiments are also underway. Ear-field sound predictions of diffuser flow are currently underway. Coupled diffuser-combustor studies addressing unsteady inlet flow effects and trapped-vortex combustor studies focusing on cavity acoustic resonance effects are planned. 

Fig. 3 Starting synthetic jet. The first two ingestion/ expulsion cycles are visualized. In the first cycle a laminar vortex ring emanates from the orifice in a stationary domain. The following vortex ring is turbulent due to chaotic motion inside the cavity after the ingestion period, (a) Original LIT visualization, (b) After postprocessing calculation to identify sharp gradient lines...

The effect of polymer solutions, ejected at very small flow rates at the tip of a finite span hydrofoil, on the inception and extent of tip vortex cavitation is investigated. The results show that the dessinent cavitation numbers are significantly reduced by polymer additives as compared with those in pure water. Moreover, for operating conditions well below critical, the presence of polymer in the vortex core results in the nearly complete elimination of the vapour cavity. These effects can be interpreted on the basis of a modification of the velocity field due to the viscoelastic properties of the polymer solutions. L.D.A. measurements indicate a large decrease of the tangential velocity component in the transition region between the inner solid body rotation co.e and the outer potential vortex flow. Also, a change of the slope of the velocity within the core is observed. 

Vortex shedding and acoustic resonance can have a "tuning effect, forcing their frequencies into coincidence as they near each other. "Detuning baffles are sometimes required in tube bundles. These baffles are designed and located so as to modify the characteristic cavity dimension without significantly affecting the shellside flow pattern. 

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