Vorticity estimation utilizing the rotation of finite line segments

Paper presented at the 5th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 1-4 July, 2007.In a fluid flow field where velocities are measured or numerically calculated, the vorticity value at a point in the field is usually estimated by approximating partial derivatives of velocity with ratios of velocity differences and spatial differences. Based on the fundamental definition of rotation, this paper presents an alternate approach to estimate vorticity, by using the instantaneous relative angular velocity of finite line segments radiating from the point to adjacent points in the fluid. The number, length and placement of line segments are varied to find their effects on predicted vorticity values in four laminar flow fields with known vorticity. Equations are also derived for a configuration consisting of four independent finite line segments which has application to a square numerical velocity mesh and to instrumentation such as hot wire vorticity probes and vane vorticity meters. The results presented are relevant to both experimental and computational fluid mechanics.cs201

Measurement of the Charged Multiplicities in b, c and Light Quark Events from Z0 Decays

Average charged multiplicities have been measured separately in $b$, $c$ and light quark ($u,d,s$) events from $Z^0$ decays measured in the SLD experiment. Impact parameters of charged tracks were used to select enriched samples of $b$ and light quark events, and reconstructed charmed mesons were used to select $c$ quark events. We measured the charged multiplicities: $\bar{n}_{uds} = 20.21 \pm 0.10 (\rm{stat.})\pm 0.22(\rm{syst.})$, $\bar{n}_{c} = 21.28 \pm 0.46(\rm{stat.}) ^{+0.41}_{-0.36}(\rm{syst.})$ $\bar{n}_{b} = 23.14 \pm 0.10(\rm{stat.}) ^{+0.38}_{-0.37}(\rm{syst.})$, from which we derived the differences between the total average charged multiplicities of $c$ or $b$ quark events and light quark events: $\Delta \bar{n}_c = 1.07 \pm 0.47(\rm{stat.})^{+0.36}_{-0.30}(\rm{syst.})$ and $\Delta \bar{n}_b = 2.93 \pm 0.14(\rm{stat.})^{+0.30}_{-0.29}(\rm{syst.})$. We compared these measurements with those at lower center-of-mass energies and with perturbative QCD predictions. These combined results are in agreement with the QCD expectations and disfavor the hypothesis of flavor-independent fragmentation.Comment: 19 pages LaTex, 4 EPS figures, to appear in Physics Letters

Purge and Mainstream Flow Interaction Control by Means of Platform Circumferential Contouring

This study presents an attempt to reduce the losses produced by the purge flow in a turbine stage by incorporating circumferential platform contouring. Two contours are proposed and compared against a baseline at different levels of swirl. The computational simulations were performed using a RANS three-dimensional Computational Fluid Dynamics code with the Shear Stress Transport turbulence model. The results of steady simulations demonstrate that for the first contour, when the flow is swirled to 50% of the rim speed, the purge flow exits the cavity with less cross flow. This in turn reduces the strength of the passage vortex. However, at swirl extremes of 0% and 100% the baseline has the best perfomance. The results show that a carefully desgined platform could reduce losses when the operating condition is in the proximity of 50% swirl. © 2011 by Siemens Energy, Inc