scholarly journals Study of Radial Wall Jets from Ceiling Diffusers at Variable Air Volume

Energies ◽  
2021 ◽  
Vol 14 (1) ◽  
pp. 240
Author(s):  
Maria Hurnik ◽  
Jan Kaczmarczyk ◽  
Zbigniew Popiolek
Keyword(s):  
Velocity Distribution ◽  
The Self ◽  
Air Velocity ◽  
Self Similarity ◽  
Wall Jets ◽  
Radial Wall ◽  
Variable Air Volume ◽  
Air Volume ◽  
Terminal Zone ◽  
The Mean

The knowledge of the air velocity distribution in the supply jets is essential when designing ventilation and air conditioning systems. In this study, we tested and analyzed the velocity distributions in the radial wall jets—these jets are commonly used in ventilated rooms. Tests included jets from two ceiling diffusers of different constructions, at three airflow rates. The mean air speed distributions were measured with a 16-channel hot-sphere anemometer both in the self-similarity zone and in the terminal zone. A specially developed method of converting the mean speed to mean velocity was used. The measurement results show that the spread coefficients of the jets from both diffusers were the same, but the positions of the virtual origin were different. Due to the friction of the jet with the ceiling and the transfer of momentum to the recirculating flows, the momentum flux in the self-similarity zone decreased by up to 50%. An improved method for calculating velocity distributions in radial wall jets was developed and validated. This method takes into account the decrease of momentum, non-zero position of the jet origin, and faster velocity decrease in the terminal zone. A reliable method of predicting air velocity distribution in radial wall jets (RWJs) from ceiling diffusers may allow to properly select the diffuser size, its location, and the range of flow rate changes. The design process for variable air volume systems can be facilitated.

Self-Similarity Analysis of Turbulent Wake Flows

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
Tie Wei
Keyword(s):  
Transverse Velocity ◽  
Maximum Velocity ◽  
Turbulent Wake ◽  
The Self ◽  
Similarity Analysis ◽  
Stream Velocity ◽  
Self Similarity ◽  
Layer Width ◽  
Wake Flows ◽  
The Mean

This paper investigates the self-similarity properties in the far downstream of high Reynolds number turbulent wake flows. The growth rate of the wake layer width, dδ/dx; the decaying rate of the maximum velocity defect, dUs/dx; and the scaling for the maximum mean transverse (across the stream) velocity, Vmax, are derived directly from the self-similarity of the continuity equation and the mean momentum equation. The analytical predictions are validated with the experimental data. Using an approximation function for the mean axial flow, the self-similarity analysis yields approximate solutions for the mean transverse velocity, V, and the Reynolds shear stress, T=−〈uv〉. Close relations among the shapes of U, V, and T are revealed.

scholarly journals Simultaneous skin friction and velocity measurements in high Reynolds number pipe and boundary layer flows

2019 ◽  
Vol 871 ◽  
pp. 377-400 ◽  
Author(s):  
R. Baidya ◽  
W. J. Baars ◽  
S. Zimmerman ◽  
M. Samie ◽  
R. J. Hearst ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Skin Friction ◽  
Large Scale ◽  
Streamwise Velocity ◽  
Momentum Equation ◽  
The Self ◽  
Self Similarity ◽  
Self Similar ◽  
The Mean ◽  
High Reynolds

Streamwise velocity and wall-shear stress are acquired simultaneously with a hot-wire and an array of azimuthal/spanwise-spaced skin friction sensors in large-scale pipe and boundary layer flow facilities at high Reynolds numbers. These allow for a correlation analysis on a per-scale basis between the velocity and reference skin friction signals to reveal which velocity-based turbulent motions are stochastically coherent with turbulent skin friction. In the logarithmic region, the wall-attached structures in both the pipe and boundary layers show evidence of self-similarity, and the range of scales over which the self-similarity is observed decreases with an increasing azimuthal/spanwise offset between the velocity and the reference skin friction signals. The present empirical observations support the existence of a self-similar range of wall-attached turbulence, which in turn are used to extend the model of Baarset al.(J. Fluid Mech., vol. 823, p. R2) to include the azimuthal/spanwise trends. Furthermore, the region where the self-similarity is observed correspond with the wall height where the mean momentum equation formally admits a self-similar invariant form, and simultaneously where the mean and variance profiles of the streamwise velocity exhibit logarithmic dependence. The experimental observations suggest that the self-similar wall-attached structures follow an aspect ratio of$7:1:1$in the streamwise, spanwise and wall-normal directions, respectively.

scholarly journals Investigation of the regularities of vortical flows in a cyclone-bed chamber

2018 ◽  
Vol 63 (3) ◽  
pp. 307-317
Author(s):  
E. A. Pitsukha ◽  
E. K. Buchilko ◽  
Yu. S. Teplitskii
Keyword(s):  
Froude Number ◽  
Fluidized Bed ◽  
Similarity Theory ◽  
Longitudinal Velocity ◽  
Blast Temperature ◽  
Air Velocity ◽  
Self Similarity ◽  
Vortex Zone ◽  
Pressure Distributions ◽  
Air Volume

Experimental investigation of the radial distributions of tangential and longitudinal velocities, total and static pressures in the vortex zone of a cyclone-bed chamber of diameter 0.21 m has been carried out. The experiments were carried out at various regime parameters (fraction of bottom blast, total air volume flow) and geometric parameters (diameter and shape of the outlet) of the chamber, and also in the presence of a fixed or fluidized bed of granular material. The influence of nonisotherm of bottom and tangential blast on the distribution pattern of velocity and pressure in the vortex zone of the cyclone-bed chamber is investigated. There was determined the influence of bottom blast temperature on the longitudinal velocity of air in the central part of the vortex zone chamber.  It is shown that the diameter of the outlet has a significant effect on the pressure in the chamber. The longitudinal velocity in the central part of the chamber is practically independent of the shape of the outlet. The presence of the fluidized bed has an effect on the hydrodynamics of the cyclone-bed chamber vortex zone. In the presence of the fluidized bed there has been a violation of the self-similarity of hydrodynamic dimensionless parameters distribution in the vortex zone. The obtained experimental data were summarized within the framework of the similarity theory with the use of a dimensionless quantity characterizing the hydrodynamics of an inhomogeneous fluidized bed – the Froude number (Fr). The use of the Froude number makes it possible to take into account the effect of the fluidized bed hydrodynamics on the features of air velocity and pressure distributions in the vortex zone, and also takes into account the influence of such an important factor as the fraction of bottom blast.

A Comparison of Physiological Demand between Self-Propelled and Motorized Treadmill Exercise

2018 ◽  
Vol 7 (4) ◽  
pp. 13-21
Author(s):  
Todd Backes ◽  
Charlene Takacs
Keyword(s):  
Respiratory Exchange Ratio ◽  
Treadmill Exercise ◽  
Cardiopulmonary Exercise Testing ◽  
Mean Value ◽  
The Self ◽  
Mixing Chamber ◽  
Wide Range ◽  
The Subject ◽  
The Mean ◽  
Computer Controlled

There are a wide range of options for individuals to choose from in order to engage in aerobic exercise; from outdoor running to computer controlled and self-propelled treadmills. Recently, self-propelled treadmills have increased in popularity and provide an alternative to a motorized treadmill. Twenty subjects (10 men, 10 women) ranging in age from 19-23 with a mean of 20.4 ± 0.8 SD were participants in this study. The subjects visited the laboratory on three occasions. The purpose of the first visit was to familiarize the subject with the self-propelled treadmill (Woodway Curve 3.0). The second visit, subjects were instructed to run on the self-propelled treadmill for 3km at a self-determined pace. Speed data were collected directly from the self-propelled treadmill. The third visit used speed data collected during the self-propelled treadmill run to create an identically paced 3km run for the subjects to perform on a motorized treadmill (COSMED T150). During both the second and third visit, oxygen consumption (VO2) and respiratory exchange ratio (R) data were collected with COSMED’s Quark cardiopulmonary exercise testing (CPET) metabolic mixing chamber system. The VO2 mean value for the self-propelled treadmill (44.90 ± 1.65 SE ml/kg/min) was significantly greater than the motorized treadmill (34.38 ± 1.39 SE ml/kg/min). The mean R value for the self-propelled treadmill (0.91 ± 0.01 SE) was significantly greater than the motorized treadmill (0.86 ± 0.01 SE). Our study demonstrated that a 3km run on a self-propelled treadmill does elicit a greater physiological response than a 3km run at on a standard motorized treadmill. Self-propelled treadmills provide a mode of exercise that offers increased training loads and should be considered as an alternative to motorized treadmills.

scholarly journals CAN AGN FEEDBACK BREAK THE SELF-SIMILARITY OF GALAXIES, GROUPS, AND CLUSTERS?

2014 ◽  
Vol 783 (1) ◽  
pp. L10 ◽  
Author(s):  
M. Gaspari ◽  
F. Brighenti ◽  
P. Temi ◽  
S. Ettori
Keyword(s):  
The Self ◽  
Self Similarity

COLONY OF THE FUNGUS Aspergillus oryzae AND SELF-AFFINE FRACTAL GEOMETRY OF GROWTH FRONTS

Fractals ◽  
1993 ◽  
Vol 01 (01) ◽  
pp. 11-19 ◽  
Author(s):  
SHU MATSUURA ◽  
SASUKE MIYAZIMA
Keyword(s):  
Aspergillus Oryzae ◽  
Environmental Conditions ◽  
Fractal Geometry ◽  
Nutrient Concentration ◽  
Incubation Temperature ◽  
Characteristic Exponent ◽  
Growth Front ◽  
Favorable Condition ◽  
The Self ◽  
The Mean

A variety of colony shapes of the fungus Aspergillus oryzae under varying environmental conditions such as the nutrient concentration, medium stiffness and incubation temperature are obtained, ranging from a homogeneous Eden-like to a ramified DLA-like pattern. The roughness σ(l, h) of the growth front of the band-shaped colony, where h is the mean front height within l of the horizontal range, satisfies the self-affine fractal relation under favorable environmental conditions. In the most favorable condition of our experiments, its characteristic exponent is found to be a little larger than that of the 2-dimensional Eden model.

scholarly journals On the self-similarity of diffracting gaseous detonations and the critical channel width problem

2021 ◽  
Vol 33 (6) ◽  
pp. 066106
Author(s):  
M. I. Radulescu ◽  
R. Mével ◽  
Q. Xiao ◽  
S. Gallier
Keyword(s):  
The Self ◽  
Channel Width ◽  
Self Similarity ◽  
Gaseous Detonations
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