scholarly journals Streamwise vorticity generation and mixing enhancement in free jets by 'delta-tabs'

1993 ◽  
Author(s):  
K. ZAMAN
Keyword(s):  
Mixing Enhancement ◽  
Streamwise Vorticity ◽  
Free Jets ◽  
Vorticity Generation

The flow characteristics of a confined square jet with mixing tabs

1998 ◽  
Vol 212 (2) ◽  
pp. 63-76 ◽  
Author(s):  
S C M Yu ◽  
Y X Hou ◽  
S C Low
Keyword(s):  
Flow Characteristics ◽  
Side Wall ◽  
Laser Doppler Anemometer ◽  
Mixing Enhancement ◽  
Streamwise Vortices ◽  
Streamwise Vorticity ◽  
Mean Velocity ◽  
Downstream Distance ◽  
Two Component ◽  
Breadth Ratio

The flow characteristics of a confined square jet with mixing tabs have been determined by measurements obtained using a two-component laser Doppler anemometer at a Reynolds number of 1.026 × 105 (based on the exit hydraulic diameter, DH = 60 mm, and bulk mean velocity, Ur, of the stream at 1.71 m/s). Both tabs of rectangular and triangular shapes are considered with the same height-breadth ratio ( h/b = 1.35) and with their apex leaning downstream. Altogether four tabs have been used, with one tab each located at the centre of each side wall at the exit plane. Each tab is found to produce a dominant pair of counter-rotating streamwise vortices. The combined effects of the four tabs bifurcate the jet into four ‘fingers’, resulting in a significant increase in entrainment at the downstream locations. The strength of the streamwise vorticity generated by the rectangular tabs is some 30 per cent higher than the triangular ones and decays faster with downstream distance. This appears due to a larger tab surface area which creates a larger pressure differential across the rectangular tab than the triangular tab. The region of high turbulent kinetic energy is found firstly at the locations where the streamwise vortices stretch the normal vortices and subsequently at locations where the streamwise vortices break down, resulting in significant mixing enhancement. Finally, the effects of the so-called secondary tabs have also been examined and are found to enhance the mixing further. The orientation of the secondary tabs is, however, crucial for the mixing enhancement to occur.

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.

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.

scholarly journals Mixing enhancement using chevron nozzle: studies on free jets and confined jets

Sadhana ◽  
2018 ◽  
Vol 43 (7) ◽  
Author(s):  
G Harish Subramanian ◽  
CH V S Nagarjun ◽  
K V Satish Kumar ◽  
B Ashish Kumar ◽  
Vishal Srikanth ◽  
...  
Keyword(s):  
Mixing Enhancement ◽  
Confined Jets ◽  
Free Jets ◽  
Chevron Nozzle

Mixing enhancement in compressible base flows via generation of streamwise vorticity

AIAA Journal ◽  
2001 ◽  
Vol 39 ◽  
pp. 1633-1635
Author(s):  
J. C. Ditton ◽  
C. J. Bourdon
Keyword(s):  
Mixing Enhancement ◽  
Streamwise Vorticity ◽  
Base Flows

Enhancement of Mixing Effectiveness in Skewed Streams

2004 ◽  
Author(s):  
B. Deinert ◽  
J. Hourmouziadis
Keyword(s):  
Wake Flow ◽  
Test Facility ◽  
Experimental Investigations ◽  
Mixing Enhancement ◽  
Streamwise Vortices ◽  
Streamwise Vorticity ◽  
Plane Shear ◽  
Jet Mixing ◽  
Mixing Noise ◽  
Rotational Direction

Forced mixers are used to improve the performance (thrust and SFC) and to reduce jet-mixing noise of turbofan engines. Therefore every effort has been made to enhance the mixing from forced exhaust mixers. A lobed type of forced mixer induces rapid mixing by enhancing the streamwise vorticity and increasing the interfacial area. Lobed mixer effectiveness can be further enhanced through the introduction of smaller scale mixing devices. For the design of these mixing devices it is important to keep in mind, that the devices have to produce smaller scale vorticity, but with an acceptable pressure loss. Several investigations have been reported on mixing enhancement in a plane shear layer and in wake flows using tabs. One important result was that each tab produces a dominant pair of counter-rotating streamwise vortices with a rotational direction opposite to that of the vortices generated by the induced upstream stagnation field (horseshoe vortex). Due to the high relevance for many engineering applications such as for the mixing processes behind lobed exhaust mixers in turbojet engines, the present investigation also considers skewed streams with delta tabs. In an attempt to explain the basic flow behaviour downstream of a mixing device in a constant skewed stream, qualitative and quantitative measurements have been carried out. The experiments are carried out in a low-speed test facility, which generates a two-stream skewed flow at different angles. This investigation considers the evolution of coherent structures and the characteristic flow field of parallel and skewed streams generated by mixing devices in the form of delta tabs (triangular-shaped tabs with their apex leaning downstream). Later on the results of this study are to be applied to the design of mixing devices introduced on a lobed mixer. One significant result of these experimental investigations in skewed streams is that each tab generates a pair of counter-rotating streamwise vortices with the same rotational direction as in the unskewed stream, but both vortices are not equally strong. This is caused by the fact that the pressure field ceases to be symmetric upstream of the tab. Farther downstream, the wake flow appears to be wrapped around the stronger vortex.

Mixing Enhancement in Compressible Base Flows via Generation of Streamwise Vorticity

AIAA Journal ◽  
2001 ◽  
Vol 39 (8) ◽  
pp. 1633-1635 ◽  
Author(s):  
C. J. Bourdon ◽  
J. C. Dutton
Keyword(s):  
Mixing Enhancement ◽  
Streamwise Vorticity ◽  
Base Flows

Measured and Predicted Secondary Flows in a Centrifugal Impeller

1971 ◽  
Vol 93 (1) ◽  
pp. 126-131 ◽  
Author(s):  
J. H. G. Howard ◽  
E. Lennemann
Keyword(s):  
Secondary Flows ◽  
Centrifugal Impeller ◽  
Streamwise Vorticity ◽  
Complex Flow ◽  
Primary Flow ◽  
Slip Rings ◽  
Rotating Impeller ◽  
Vorticity Generation ◽  
Hot Film ◽  
Simple Combination

The complete velocity distribution, including both primary and secondary velocities, has been measured in passages of centrifugal impellers of simple shape. Comparison is made with theoretically predicted secondary vorticities based on a simple combination of an inviscid primary flow and a streamwise vorticity generation analysis. The measured velocities were obtained in a water-flow impeller rig using a miniature, cylindrical, hot-film probe positioned on the rotating impeller and traversed and controlled remotely through slip rings. The understanding of the complex flow patterns was assisted by a photographic study employing a hydrogen bubble, flow visualization technique.

Mixing Enhancement in Free Jets from Supersonic ESTS Lobed Nozzles

2017 ◽  
pp. 95-99
Author(s):  
Albin Varghese ◽  
S. K. Karthick ◽  
Srisha M. V. Rao ◽  
Gopalan Jagadeesh
Keyword(s):  
Mixing Enhancement ◽  
Free Jets
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