Secondary vortices in swirling flow

Twisted tapes are used to induce swirling flow and improve mixing. The flow induced by a 180 degree twisted tape with length (pitch) 60 mm and diameter 25.4 mm in a circular pipe was investigated using Laser Doppler Velocimetry (LDV) measurements. Tangential velocity profiles downstream of the twisted tape swirler were measured at multiple locations along the pipe axis, across the horizontal diameter of the pipe. The profiles showed an unexpected transition along the pipe axis from regular swirling flow to an apparent counter-rotation near the pipe axis, and then reverting back to regular swirling flow. Injecting fine air bubbles into the flow showed the existence of two co-rotating helical vortices superimposed over the main swirling flow. The close proximity of the two co-rotating vortices creates the local reversing flow at the pipe centerline. The secondary vortices are analyzed with high speed camera videos and numerical simulations.Comment: 2 videos include

Non-premixed Flame-Turbulence Interaction in Compressible Turbulent Flow

Nonpremixed turbulent reacting flows are intrinsically difficult to model due to the strong coupling between turbulent motions and reaction. The large amount of heat released by a typical hydrocarbon flame leads to significant modifications of the thermodynamic variables and the molecular transport coefficients and thus alters the fluid dynamics. Additionally, in nonpremixed combustion, the flame has a complex spatial structure. Localized expansions and contractions occur, enhancing the dilatational motions. Therefore, the compressibility of the flow and the heat release are intimately related. However, fundamental studies of the role of compressibility on the scalar mixing and reaction are scarce. In this paper we present results concerning the fundamental aspects of the interaction between non-premixed flame and compressible turbulence.Comment: 4 pages, 4 figures; to appear in Proceedings ETC9, Eds: I.P. Castro and P.E. Hancock, CIMNE, Barcelona, 200

A Note On The Lack Of Statistical Optimality In The Judgment Of Solomon

Solomon, in his most celebrated decision, threatened to cut a baby in half, calculated to elicit such testimony from a claimant that would allow him to identify the real mother and thus grant her custody. Comment from biblical scholars seems to run in the same direction, i.e. Solomon had insight into maternal love. When one of the females offered to withdraw her claim, to save the child, he identified her as the real mother, and this provided the foundation for his Judgment. While the evidentiary trap set by Solomon is genius, his use of the data produced by his trap lacked statistical optimality. The optimality of Solomon’s decision has never been challenged in the literature until now. This challenge is long overdue, considering the fact that this decision has been enshrined as the icon of “Superb decision making” in many cultures including our own. This paper points out that, in view of the testimony of the second woman, the optimal decision would have been to identify the second woman as an imposter. Custody should have been given to the first woman by default

Cellular Blood Flow

The fluid dynamics video that is presented here outlines recent advances in the simulation of multiphase cellular blood flow through the direct numerical simulations of deformable red blood cells (RBCs) demonstrated through several numerical experiments. Videos show particle deformation, shear stress on the particle surface, and the formation of particle clusters in both Hagen-Poiseuille and shear flow.Comment: 2 pages, one hyperlink to 2 video

Experimental Investigation of Steady Flows at a Breached Levee

Steady flow at a breached levee is studied in this dissertation through a generalized model and a case study. The generalized experimental set-up consists of a main channel with an opening in its side wall and an adjustable sluice gate at its downstream end. Water surface elevation and the three-dimensional velocity field are measured by a point gauge and an Acoustic Doppler Velocimeter (ADV), respectively. Time-averaged measured values of velocity field and free surface elevation are presented. In addition, Froude Number, turbulent kinetic energy (TKE) and bed shear stress are computed from the measured results. Results show that the flow is one-dimensional near the inlet and outlet of the main channel. However, it is three-dimensional near the breach. There is a zone of depression having dimensions less than the breach length near the breach in the surface profile. The Froude Number indicates the flow is critical near the breach. The bed shear stress shows that the breach area is prone to erosion. A generalized analytical model is developed to predict the approximate flow depth and velocity at the breach by knowing the flow depths at inlet and outlet, discharge at inlet, channel widths and breach length. The 17th Street Canal breach is employed as a case study. Detailed measurements of th