scholarly journals Roles of Streamwise and Transverse Partial-Vorticity Components in Steady Inviscid Isentropic Supercell-Like Flows

2017 ◽  
Vol 74 (9) ◽  
pp. 3021-3041 ◽  
Author(s):  
Robert Davies-Jones
Keyword(s):  
Temperature Gradients ◽  
Streamwise Vorticity ◽  
Flow Vorticity ◽  
Unstable Environment ◽  
Vorticity Component ◽  
Analytical Formulas ◽  
Transverse Temperature ◽  
Vorticity Generation ◽  
Strong Vortex ◽  
River Bend

Abstract Investigations of tornadogenesis in supercells attempt to find the origin of the tornado’s large vorticity by determining vorticity generation and amplification along trajectories that enter the tornado from a horizontally uniform unstable environment. Insights into tornadogenesis are provided by finding analytical formulas for vorticity variations along streamlines in idealized, steady, inviscid, isentropic inflows of dry air imported from the environment. The streamlines and vortex lines lie in the stationary isentropic surfaces so the vorticity is 2D. The transverse vorticity component (positive leftward of the streamlines) arises from imported transverse vorticity and from baroclinic vorticity accumulated in streamwise temperature gradients. The streamwise component stems from imported streamwise vorticity, from baroclinic vorticity accrued in transverse temperature gradients, and from positive transverse vorticity that is turned streamwise in cyclonically curved flow by a “river-bend process.” It is amplified in subsiding air as it approaches the ground. Streamwise stretching propagates a parcel’s streamwise vorticity forward in time. In steady flow, vorticity decomposes into baroclinic vorticity and two barotropic parts ωBTIS and ωBTIC arising from imported storm-relative streamwise vorticity (directional shear) and storm-relative crosswise vorticity (speed shear), respectively. The Beltrami vorticity ωBTIS is purely streamwise. It explains why abundant environmental storm-relative streamwise vorticity close to ground favors tornadic supercells. It flows directly into the updraft base unmodified apart from streamwise stretching, establishing mesocyclonic rotation and strong vortex suction at low altitudes. Increase (decrease) in storm-relative environmental wind speed with height near the ground accelerates (delays) tornadogenesis as positive (negative) ωBTIC is turned into streamwise (antistreamwise) vorticity within cyclonically curved flow around the mesocyclone.

Distortion of Three-Dimensional Vorticity Waves by a Cascade of Airfoils

1989 ◽  
Author(s):  
J. Fang ◽  
P. R. McHugh ◽  
H. M. Atassi
Keyword(s):  
Unsteady Flow ◽  
Long Range ◽  
Subsonic Flow ◽  
Rotational Velocity ◽  
Three Dimensional ◽  
Blade Surface ◽  
Streamwise Vorticity ◽  
Vorticity Component ◽  
Analytical Expressions

The evolution of three-dimensional vorticity waves impinging on a cascade of loaded blades in subsonic flow is studied. Analytical expressions are derived for the streamwise, normal and spanwise components of the vorticity and the associated rotational velocity. These unsteady flow quantities are calculated, and their variations analyzed and plotted for a typical loaded cascade. The results show that at large distances from the blades a slow but long range distortion of the incoming vorticity waves takes place. Near the blade surface, the stretching and turning of the vorticity produce large values for the streamwise vorticity component.

Improving the Accuracy of Multihole Probe Measurements in Velocity Gradients

2008 ◽  
Author(s):  
Valery Chernoray ◽  
Johan Hja¨rne
Keyword(s):  
Size Effects ◽  
Three Dimensional ◽  
Finite Size ◽  
Correction Method ◽  
Single Step ◽  
Streamwise Vorticity ◽  
Finite Size Effects ◽  
Good Efficiency ◽  
Vorticity Component ◽  
Crossflow Velocity

This study describes an implementation and verification of an effective and reliable correction for the finite-size effects of pressure probes. A modified version of correction by Ligrani et al. (Exp. Fluids, vol. 7, 1989, p. 424) was used. It is shown that the correction procedure can be implemented in two steps as in Ligrani et al. or in a single step, either for probe pressures, or for velocity components. The latter correction method is found to have the best performance and studied in very detail. The effect of the correction in application to the highly three-dimensional flow downstream of the outlet guide vanes is scrutinized through detailed side-by-side comparison with corresponding cross hot-wire data. The influence of the correction on all three velocity components, flow streamlines and streamwise vorticity fields is thoroughly examined. Two flow cases with different incoming turbulence intensities are considered. The study demonstrates a very good efficiency and reliability of the correction, which lead to a significant improvement of the corrected velocity data. The improvement in crossflow velocity components has allowed correct description of the flow streamlines, and as a result, the secondary flow field structures were resolved more accurately. The considered correction does not affect the streamwise vorticity component, which is clarified as well. A very important fact is that the correction is not found to over-correct and distort the data, thus can be used safely. A very good performance of the correction for the finite-size effects of pressure probes presented in this study allows us to recommend it as a mandatory step in postprocessing procedures for multihole pressure probes.

Role of transverse temperature gradients in the generation of lamellar eutectic solidification patterns

2010 ◽  
Vol 58 (5) ◽  
pp. 1761-1769 ◽  
Author(s):  
Mikaël Perrut ◽  
Andrea Parisi ◽  
Silvère Akamatsu ◽  
Sabine Bottin-Rousseau ◽  
Gabriel Faivre ◽  
...  
Keyword(s):  
Temperature Gradients ◽  
Eutectic Solidification ◽  
Lamellar Eutectic ◽  
Transverse Temperature

Simultaneous Dual-Doppler and Mobile Mesonet Observations of Streamwise Vorticity Currents in Three Supercells

2020 ◽  
Vol 148 (12) ◽  
pp. 4859-4874
Author(s):  
Shawn S. Murdzek ◽  
Paul M. Markowski ◽  
Yvette P. Richardson
Keyword(s):  
High Resolution ◽  
Laminar Flow ◽  
Turbulent Flow ◽  
Numerical Simulations ◽  
Cross Sections ◽  
The Other ◽  
Streamwise Vorticity ◽  
Vorticity Generation ◽  
Southern Fringe

AbstractRecent high-resolution numerical simulations of supercells have identified a feature referred to as the streamwise vorticity current (SVC). Some have presumed the SVC to play a role in tornadogenesis and maintenance, though observations of such a feature have been limited. To this end, 125-m dual-Doppler wind syntheses and mobile mesonet observations are used to examine three observed supercells for evidence of an SVC. Two of the three supercells are found to contain a feature similar to an SVC, while the other supercell contains an antistreamwise vorticity ribbon on the southern fringe of the forward flank. A closer examination of the two supercells with SVCs reveals that the SVCs are located on the cool side of boundaries within the forward flank that separate colder, more turbulent flow from warmer, more laminar flow, similar to numerical simulations. Furthermore, the observed SVCs are similar to those in simulations in that they appear to be associated with baroclinic vorticity generation and have similar appearances in vertical cross sections. Aside from some apparent differences in the location of the maximum streamwise vorticity between simulated and observed SVCs, the SVCs seen in numerical simulations are indeed similar to reality. The SVC, however, may not be essential for tornadogenesis, at least for weak tornadoes, because the supercell that did not have a well-defined SVC produced at least one brief, weak tornado during the analysis period.

Characteristics of vorticity fluctuations in a turbulent wake

1988 ◽  
Vol 189 ◽  
pp. 349-365 ◽  
Author(s):  
R. A. Antonia ◽  
L. W. B. Browne ◽  
D. A. Shah
Keyword(s):  
Circular Cylinder ◽  
Turbulent Wake ◽  
Probability Density Functions ◽  
The Self ◽  
Density Functions ◽  
Streamwise Vorticity ◽  
Local Isotropy ◽  
Vorticity Component ◽  
Vorticity Fluctuation ◽  
Made In

Measurements of the lateral components of the vorticity fluctuation have been made in the self-preserving turbulent wake of a circular cylinder. Each component was obtained separately using two X-wires separated in the appropriate lateral directions. The two velocity derivatives which make up the streamwise vorticity component were also determined but not simultaneously. An approximation to the streamwise vorticity was made from these measurements. Moments, probability density functions and spectra of the three vorticity components across the wake are presented and discussed. The high-wavenumber behaviour of the spectra is compared with calculations, based on local isotropy. Satisfactory agreement with the calculations is obtained for the lateral vorticity components over a significant high-wavenumber range. The approximated streamwise vorticity spectrum tends towards the isotropic calculation at very large wavenumbers.

Effects of Variable Thermal Properties on Moving-Band-Source Temperatures

1975 ◽  
Vol 97 (3) ◽  
pp. 1074-1078 ◽  
Author(s):  
J. Isenberg ◽  
S. Malkin
Keyword(s):  
Thermal Properties ◽  
Thermal Stresses ◽  
Temperature Gradients ◽  
Heat Sources ◽  
Moving Heat Source ◽  
Constant Property ◽  
Surface Temperatures ◽  
Transverse Temperature ◽  
Property Model ◽  
Moving Band

Temperatures calculated by moving-heat-source theory for machining and sliding processes are often sufficiently large that the assumption of temperature-independent thermal properties is invalid. In the present paper results of a numerical analysis are presented that consider the effects of variable thermal properties on the temperatures due to a moving-band source. Compared with the constant-property model, the maximum surface temperatures are found to be significantly higher with small Peclet numbers and strong heat sources, but the average surface temperatures within the band are much less affected by the variations of thermal properties with temperature. The variable-property model also indicates significantly larger transverse temperature gradients, a phenomenon that should cause greater thermal stresses.

scholarly journals Hysteretic and chaotic dynamics of viscous drops in creeping flows with rotation

2008 ◽  
Vol 607 ◽  
pp. 209-234 ◽  
Author(s):  
Y.-N. YOUNG ◽  
J. BŁAWZDZIEWICZ ◽  
V. CRISTINI ◽  
R. H. GOODMAN
Keyword(s):  
Length Distribution ◽  
Period Doubling ◽  
Small Deformation ◽  
High Viscosity ◽  
Boundary Integral ◽  
Drop Shape ◽  
Viscous Drops ◽  
Flow Vorticity ◽  
Creeping Flows ◽  
Vorticity Component

We have shown that high-viscosity drops in two-dimensional linear creeping flows with a non-zero vorticity component may have two stable stationary states. One state corresponds to a nearly spherical, compact drop stabilized primarily by rotation, and the other to an elongated drop stabilized primarily by capillary forces. Here we explore consequences of the drop bistability for the dynamics of highly viscous drops. Using both boundary-integral simulations and small-deformation theory we show that a quasi-static change of the flow vorticity gives rise to a hysteretic response of the drop shape, with rapid changes between the compact and elongated solutions at critical values of the vorticity. In flows with sinusoidal temporal variation of the vorticity we find chaotic drop dynamics in response to the periodic forcing. A cascade of period-doubling bifurcations is found to be directly responsible for the transition to chaos. In random flows we obtain a bimodal drop-length distribution. Some analogies with the dynamics of macromolecules and vesicles are pointed out.

A numerical investigation of the effects of a transverse temperature gradient on the formation of regular and irregular acoustic streaming in an enclosure

2010 ◽  
Vol 225 (1) ◽  
pp. 132-144 ◽  
Author(s):  
M K Aktas ◽  
T Ozgumus
Keyword(s):  
Temperature Gradient ◽  
Stokes Equations ◽  
Acoustic Streaming ◽  
Fluid Motion ◽  
Sound Field ◽  
Flow Patterns ◽  
Temperature Gradients ◽  
Left Wall ◽  
Steady Streaming ◽  
Transverse Temperature

The effects of a transverse temperature gradient on the formation of regular and irregular acoustic streaming structures in air-filled, two-dimensional, rectangular, shallow enclosures carrying a longitudinal sound field are investigated numerically. The fluid motion is induced by the harmonic vibration of the enclosure left wall. The fully compressible form of the Navier—Stokes equations is considered to predict the primary oscillatory and secondary pseudo-steady streaming flow fields. An explicit time-marching flux-corrected transport algorithm is used to simulate the acoustic wave formation, propagation, and the resulting flow patterns in the enclosure. The vertical walls of the enclosure are adiabatic whereas the horizontal walls are heated differentially or symmetrically. The transverse temperature gradients are found to strongly affect the acoustic streaming structures and the velocities. The steady streaming velocities significantly increase when the enclosure horizontal walls are asymmetrically heated for both regular and irregular streaming flows. For irregular streaming, the transverse temperature gradients completely change the flow patterns. The irregular streaming velocities are greatly reduced in case of the symmetric temperature increase of the horizontal walls.

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