Edge turbulence velocity preceding the L-H transition in NSTX

2021 ◽  
Vol 28 (3) ◽  
pp. 032304
Author(s):  
S. J. Zweben ◽  
A. Diallo ◽  
M. Lampert ◽  
T. Stoltzfus-Dueck ◽  
S. Banerjee
Keyword(s):  
Author(s):  
D Guerrato ◽  
J M Nouri ◽  
N Stosic ◽  
C Arcoumanis ◽  
I K Smith

The angle-resolved mean velocity and turbulence characteristics of axial air flow within the rotors and discharge chambers of a screw compressor have been measured, using a laser Doppler velocimeter with high spatial and temporal resolution. The measurements were made through special transparent windows fixed in the compressor casing and in the pipe immediately above the discharge port. Results were obtained at a speed of 1000 r/min, a discharge pressure 1 bar, and a temperature of 57 °C. The flow interaction between the rotors and the discharge chamber was established as well as the spatial variation of the axial mean velocity and turbulence velocity fluctuation. It was shown that the discharge flow was complex, strongly time-dependent, and controlled by several mechanisms. In general, the axial velocity, on entering the working chamber downstream of the discharge port exit was higher than that immediately upstream with large variation in mean and root mean square velocities immediately after the opening of the discharge port, then flow becomes more uniform. The high velocity values and large fluctuation are mainly controlled by the pressure gradient across the port at the very beginning of the discharge process, after that, as the port opens wider, uniform flow is influenced mainly by the rotor action. These measurements will be used as input data for more reliable optimization of compressor design and to validate a computational fluid dynamics model of fluid flow within twin screw compressors, already developed in-house.


2008 ◽  
Vol 20 (3) ◽  
pp. 035108 ◽  
Author(s):  
Hideaki Mouri ◽  
Akihiro Hori ◽  
Masanori Takaoka

1975 ◽  
Vol 70 (1) ◽  
pp. 37-57 ◽  
Author(s):  
Ronald M. C. So

Assuming the turbulence length scale to be unaffected by streamline curvature, a turbulence velocity scale for curved shear flows is derived from the Reynolds-stress equations. Closure of the equations is obtained by using the scheme of Mellor & Herring (1973), and the Reynolds-stress equations are simplified by invoking the two-dimensional boundary-layer approximations and assuming that production of turbulent energy balances viscous dissipation. The resulting formula for the velocity scale has one free parameter, but this can be determined from data for non-rotating unstratified plane flows. Consequently there is no free constant in the derived expression. A single value of the constant is found to give good agreement between calculated and measured values of the velocity scale for a wide variety of curved shear flows.The result is also applied to test the validity and extent of the analogy between the effects of buoyancy and streamline curvature. This is done by comparing the present result with that obtained by Mellor (1973). Excellent agreement is obtained for the range −0·21 [les ]Rif[les ] 0·21. Therefore the present result provides direct evidence in support of the use of a Monin–Oboukhov (1954) formula for curved shear flows as proposed by Bradshaw (1969).


1996 ◽  
Vol 49 (5) ◽  
pp. 299-315 ◽  
Author(s):  
Carl H. Gibson

Flows in natural bodies of fluid often become turbulent, with eddy-like motions dominated by inertial-vortex forces. Buoyancy, Coriolis, viscous, self-gravitational, electromagnetic, and other force constraints produce a complex phase space of wave-like hydrodynamic states that interact with turbulence eddies, masquerade as turbulence, and preserve information about previous hydrodynamic states as fossil turbulence. Evidence from the ocean, atmosphere, galaxy and universe are compared with universal similarity hypotheses of Kolmogorov (1941, 1962) for turbulence velocity u, and extensions to scalar fields θ like temperature mixed by turbulence. Universal u and θ spectra of natural flows can be inferred from laboratory and computer simulations with satisfactory accuracy, but higher order spectra and the intermittency constant u of the third Kolmogorov hypothesis (1962) require measurements at the much larger Reynolds numbers found only in nature. Information about previous hydrodynamic states is preserved by Schwarz viscous and turbulence lengths and masses of self-gravitating condensates (rarely by the classical Jeans length and mass), as it is by Ozmidov, Hopfinger and Fernando scales in hydrophysical fields of the ocean and atmosphere. Viscous-gravitational formation occurred 104-105 y after the Big Bang for supercluster, cluster, and then galaxy masses of the plasma, producing the first turbulence. Condensation after plasma neutralization of the H-4He gas was to a primordial fog of sub-solar particles that persists today in galactic halos as dark matter. These gradually formed all stars, star clusters, etc (humans!) within.


2020 ◽  
Vol 5 (2) ◽  
pp. 519-541 ◽  
Author(s):  
Felix Kelberlau ◽  
Jakob Mann

Abstract. Turbulence velocity spectra are of high importance for the estimation of loads on wind turbines and other built structures, as well as for fitting measured turbulence values to turbulence models. Spectra generated from reconstructed wind vectors of Doppler beam swinging (DBS) wind lidars differ from spectra based on one-point measurements. Profiling wind lidars have several characteristics that cause these deviations, namely cross-contamination between the three velocity components, averaging along the lines of sight and the limited sampling frequency. This study focuses on analyzing the cross-contamination effect. We sample wind data in a computer-generated turbulence box to predict lidar-derived turbulence spectra for three wind directions and four measurement heights. The data are then processed with the conventional method and with the method of squeezing that reduces the longitudinal separation distances between the measurement locations of the different lidar beams by introducing a time lag into the data processing. The results are analyzed and compared to turbulence velocity spectra from field measurements with a Windcube V2 wind lidar and ultrasonic anemometers as reference. We successfully predict lidar-derived spectra for all test cases and found that their shape is dependent on the angle between the wind direction and the lidar beams. With conventional processing, cross-contamination affects all spectra of the horizontal wind velocity components. The method of squeezing improves the spectra to an acceptable level only for the case of the longitudinal wind velocity component and when the wind blows parallel to one of the lines of sight. The analysis of the simulated spectra described here improves our understanding of the limitations of turbulence measurements with DBS profiling wind lidar.


2012 ◽  
Vol 54 (11) ◽  
pp. 112001 ◽  
Author(s):  
B Cao ◽  
S J Zweben ◽  
D P Stotler ◽  
M Bell ◽  
A Diallo ◽  
...  

2007 ◽  
Vol 19 (5) ◽  
pp. 055101 ◽  
Author(s):  
Hideaki Mouri ◽  
Akihiro Hori ◽  
Yoshihide Kawashima

2018 ◽  
Vol 45 (21) ◽  
pp. 11,817-11,826 ◽  
Author(s):  
Tomas Chor ◽  
Di Yang ◽  
Charles Meneveau ◽  
Marcelo Chamecki

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