scholarly journals An Experimental Method for Generating Shear-Free Turbulence Using Horizontal Oscillating Grids

Water ◽  
2020 ◽  
Vol 12 (2) ◽  
pp. 591 ◽  
Author(s):  
Wenjie Li ◽  
Peng Zhang ◽  
Shengfa Yang ◽  
Xuhui Fu ◽  
Yi Xiao
Keyword(s):  
Experimental Method ◽  
Turbulent Flows ◽  
Dissipation Rate ◽  
Suspended Particles ◽  
Natural Environments ◽  
Water Tank ◽  
Frequency Spectra ◽  
Experimental Apparatus ◽  
Oscillating Grids ◽  
Oscillating Mode

An experimental apparatus driven by horizontal oscillating grids in a water tank is proposed for generating shear-free turbulence, which is measured using Particle Image Velocimetry (PIV). The performances of the proposed apparatus are investigated through the instantaneous and root-mean-square (RMS) velocity, Reynolds stress, length and time scale, frequency spectra and dissipation rate. Results indicate that the turbulence at the core region of the water tank, probably 8 cm in length, is identified to be shear-free. The main advantage of the turbulence driven by horizontal oscillating mode is that the ratios of the longitudinal turbulent intensities to the vertical values are between 1.5 and 2.0, consistent with those ratios in open-channel flows. Additionally, the range of the length scale can span the typical sizes of suspended particles in natural environments, and the dissipation rate also agrees with those found in natural environments. For convenience of experimental use, a formula is suggested to calculate the RMS flow velocity, which is linearly proportional to the product of oscillating stroke and frequency. The proposed experimental method in this study appears to be more appropriate than the traditional vertical oscillating mode for studying the fundamental mechanisms of vertical migratory behavior of suspended particles and contaminants in turbulent flows.

Experimental assessment of fractal scale similarity in turbulent flows. Part 4. Effects of Reynolds and Schmidt numbers

1998 ◽  
Vol 377 ◽  
pp. 169-187 ◽  
Author(s):  
RICHARD D. FREDERIKSEN ◽  
WERNER J. A. DAHM ◽  
DAVID R. DOWLING
Keyword(s):  
Turbulent Flows ◽  
Dissipation Rate ◽  
Single Point ◽  
Energy Dissipation Rate ◽  
Scalar Dissipation ◽  
Turbulent Shear ◽  
Turbulent Shear Flow ◽  
Outer Scale ◽  
Scale Invariant ◽  
Scale Similarity

Experimental results are presented for the influence of Reynolds number on multifractal scale similarity in turbulent flows. These are obtained from single-point measurements of a dynamically passive Sc≈1 conserved scalar quantity ζ(t) in a turbulent shear flow at outer-scale Reynolds numbers of 14000[les ]Reδ[les ]110000. Statistical criteria based on the maximum allowable scale-to-scale variation L1(ε) in multiplier distributions P(Mε) from multifractal gauge sets allow accurate discrimination between multifractal and non-multifractal scaling. Results show that the surrogate scalar energy dissipation rate χs(t)≡(dζ/dt)2is found to display a scale-invariant similarity consistent with a random multiplicative cascade characterized by a bilinear multiplier distribution P(Mε) over a range of scales extending downward from the outer scaleTδ. For a range of scales extending upward from the inner (diffusive) scale TD, the dissipation rate displays a different scale-invariant similarity characterized by a uniform multiplier distribution. The former scale-invariance becomes evident in the present Sc≈1 data only when Reδ is sufficiently large. Comparisons with results from Sc 1 data indicate that this scale-invariant similarity applies when the outer-to-inner scale ratio Tδ/TD≈0.09 Re3/4δSc1/2 is greater than about 400. In contrast to the scalar dissipation rate field, the scalar field is found to lack any multifractal scale similarity.

Flows of liquid4He due to oscillating grids

2017 ◽  
Vol 832 ◽  
pp. 578-599 ◽  
Author(s):  
P. Švančara ◽  
M. La Mantia
Keyword(s):  
Turbulent Flows ◽  
Particle Tracking Velocimetry ◽  
Reynolds Numbers ◽  
Quantized Vortices ◽  
Viscous Fluids ◽  
Statistical Distributions ◽  
Small Particles ◽  
Oscillating Grids ◽  
The Mean ◽  
Cryogenic Flows

We investigate cryogenic flows of liquid4He between two grids oscillating in phase, at temperatures ranging from approximately 1.3 to 2.5 K, resulting in suitably defined Reynolds numbers up to$10^{5}$. We specifically study the flow-induced motions of small particles suspended in the fluid by using the particle tracking velocimetry technique. We focus on turbulent flows of superfluid4He that occur below approximately 2.2 K and are known to display, in certain conditions, features different from those observed in flows of classical viscous fluids, such as water. We find that, at large enough length scales, larger than the mean distance between quantized vortices, representing the quantum length scale of the flow, the shapes of the velocity and velocity increment statistical distributions are very similar to those obtained in turbulent flows of viscous fluids. The experimental outcome strongly supports the view that, in the range of investigated parameters, particles probing flows of superfluid4He behave as if they were tracking classical flows.

Vertical Mixed Jet Behavior of Orifice Nozzle

2014 ◽  
Vol 1070-1072 ◽  
pp. 1978-1981
Author(s):  
Lu Peng ◽  
Dong Jun Kim ◽  
Hei Cheon Yang
Keyword(s):  
Flow Rate ◽  
High Speed ◽  
Water Tank ◽  
Entrainment Ratio ◽  
Penetration Length ◽  
Air Compressor ◽  
Primary Fluid ◽  
Experimental Apparatus ◽  
Jet Behavior ◽  
Transfer Behavior

The objective of this study is to experimentally investigate the mixed jet and oxygen transfer behavior of a vertical orifice nozzle. The experimental apparatus consisted of an electric motor-pump, an orifice nozzle, a circulation water tank, an air compressor, a high speed camera unit and controlling or measuring accessories. The entrainment ratio was calculated using the measured primary fluid flow rate and suction air flow rate with primary flow pressure. The visualization image of vertically injected air and mixed jet issuing from the orifice nozzle was analyzed qualitatively. As the air compressor pressure increases, the penetration length of mixed jet decreases and the mass ratio and dissolved oxygen concentration increase.

scholarly journals Dissipation rate of turbulent kinetic energy in stably stratified sheared flows

2018 ◽  
Author(s):  
Sergej Zilitinkevich ◽  
Oleg Druzhinin ◽  
Andrey Glazunov ◽  
Evgeny Kadantsev ◽  
Evgeny Mortikov ◽  
...  
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Turbulent Flows ◽  
Atmospheric Chemistry ◽  
Dissipation Rate ◽  
Stable Stratification ◽  
Turbulence Closure ◽  
Atmospheric Measurements ◽  
Precise Knowledge ◽  
Budget Equation

Abstract. Over the years, the problem of dissipation rate of turbulent kinetic energy (TKE) in stable stratification remained unclear because of the practical impossibility to directly measure the process of dissipation that takes place at the smallest scales of turbulent motions. Poor representation of dissipation causes intolerable uncertainties in turbulence-closure theory and, thus, in modelling stably stratified turbulent flows. We obtain theoretical solution to this problem for the whole range of stratifications from neutral to limiting stable; and validate it via (i) direct numerical simulation (DNS) immediately detecting the dissipation rate and (ii) indirect estimates of dissipation rate retrieved via the TKE-budget equation from atmospheric measurements of other components of the TKE-budget. The proposed formulation of dissipation rate will be of use in any turbulence-closure models employing the TKE budget equation and in problems requiring precise knowledge of the high-frequency part of turbulence spectra in atmospheric chemistry, aerosol science and microphysics of clouds.

Numerical and Experimental Investigation on Flow Capacity and Erosion Wear of Blooey Line in Gas Drilling

2017 ◽  
Vol 140 (5) ◽  
Author(s):  
Zhang Ying ◽  
Lian Zhanghua ◽  
Gasser F. Abdelal ◽  
Lin Tiejun
Keyword(s):  
Experimental Method ◽  
Gas Flow ◽  
Impact Force ◽  
Fire Hazard ◽  
Gas Drilling ◽  
Drilling Rig ◽  
Flow Capacity ◽  
Experimental Apparatus ◽  
Cfd Method ◽  
The Impact

Blooey line is a discharge pipe, used to conduct gas to keep drilling rock dust and cuttings away from the drilling rig, reducing the fire hazard and transporting the cuttings to a suitable distance from the well. In this paper, the blooey line's flow capacity and erosion mechanism have been investigated by numerical and experimental method. The model of blooey line, which is commonly used in Sichuan district, China, is established by using a computational fluid dynamics (CFD) method. And, the distribution of pressure field and velocity field in the blooey line are investigated by the CFD model. And, the effect of gas flow rate on impact force and erosion is also discussed. Compared with the simulation results, an experimental apparatus of the blooey line has been conducted under the mechanical similarity principle. The impact force and pressure on the elbows are measured under different gas flow rates. The numerical simulation and experimental method proposed in this paper can provide a reference for layout optimization and flow capacity calculation of blooey line in gas drilling.

Frequency spectra of reactant fluctuations in turbulent flows

1993 ◽  
Vol 246 ◽  
pp. 489-502 ◽  
Author(s):  
George Kosály
Keyword(s):  
Turbulent Flows ◽  
Cross Correlation ◽  
Mixture Fraction ◽  
Spectral Characteristics ◽  
Mixing Layer ◽  
Correlation Coefficients ◽  
Frequency Spectra ◽  
Fast Chemistry ◽  
Limiting Values ◽  
Intermediate Rate

Bilger, Saetran & Krishnamoorthy (1991) give measured values of the variance, cross-correlation coefficient, autospectra, coherence and phase shift of the reactant concentration fluctuations for an irreversible second-order reaction in an incompressible turbulent scalar mixing layer. The present paper approaches the interpretation of the measured data by evaluating the above quantities in the frozen (slow) and equilibrium (fast) chemistry limits. We assume that the limiting values bracket the corresponding intermediate rate data.The analysis leads to values that correspond with the measured variances and correlation coefficients. The paper offers simple procedures for experimenters to evaluate the fast chemistry limit of the spectral characteristics from the measured mixture fraction fluctuations. The investigation of the limiting spectra suggests that, in the frequency region considered in the Bilger et al. measurements, the shape of the autospectrum is quite insensitive to the chemistry rate. The cross-spectrum is much more sensitive to the chemistry than the autospectrum. The analysis predicts correctly that the coherence decreases with increasing frequency while the phase stays equal to π until the decrease of the coherence leads to indeterminate phase results.

Development and Application of a Two-Scale Non-Linear Reynolds Stress Turbulence Model

2007 ◽  
Author(s):  
S. Y. Jaw ◽  
R. R. Hwang
Keyword(s):  
Turbulent Flows ◽  
Reynolds Stress ◽  
Turbulence Model ◽  
Dissipation Rate ◽  
Reynolds Stress Model ◽  
Stress Model ◽  
Turbulence Scale ◽  
Non Linear ◽  
Algebraic Reynolds Stress Model ◽  
Near Wall

To improve the prediction of turbulent flows, a two-scale, non-linear Reynolds stress turbulence model is proposed in this study. It is known that for the near-wall low-Reynolds number turbulent flows, the Kolmogorov turbulence scale, based on the fluid kinematic viscosity and dissipation rate of turbulent kinetic energy (ν,ε), is the dominant turbulence scale, hence it is adopted to address the viscous effects and the rapid increase of dissipation rate in the near wall region. As a wall is approached, the turbulence scale transits smoothly from turbulent kinetic energy based (k, ε) scale to (ν,ε) scale. The damping functions of the low-Reynolds number models can thus be simplified and the near-wall turbulence characteristics, such as the ε distribution, are correctly reproduced. Furthermore, to improve the prediction of the anisotropic Reynolds stresses for complex flows, a nonlinear algebraic Reynolds stress model is incorporated. The same turbulence scales are adopted in the nonlinear algebraic Reynolds stress model. The developed two-scale non-linear Reynolds stress model is first calibrated with the DNS budgets of two-dimensional channel flows, and then applied to predict the separation flow behind a backward facing step. It is found that the proposed two-scale nonlinear Reynolds stress turbulence model is capable of providing satisfactory results without increasing much computation efforts or causing numerical stability problems.

scholarly journals Dissipation rate of turbulent kinetic energy in stably stratified sheared flows

2019 ◽  
Vol 19 (4) ◽  
pp. 2489-2496 ◽  
Author(s):  
Sergej Zilitinkevich ◽  
Oleg Druzhinin ◽  
Andrey Glazunov ◽  
Evgeny Kadantsev ◽  
Evgeny Mortikov ◽  
...  
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Turbulent Flows ◽  
Atmospheric Chemistry ◽  
Dissipation Rate ◽  
Stable Stratification ◽  
Turbulence Closure ◽  
Atmospheric Measurements ◽  
Precise Knowledge ◽  
Budget Equation

Abstract. Over the years, the problem of dissipation rate of turbulent kinetic energy (TKE) in stable stratification remained unclear because of the practical impossibility to directly measure the process of dissipation that takes place at the smallest scales of turbulent motion. Poor representation of dissipation causes intolerable uncertainties in turbulence-closure theory and thus in modelling stably stratified turbulent flows. We obtain a theoretical solution to this problem for the whole range of stratifications from neutral to limiting stable; and validate it via (i) direct numerical simulation (DNS) immediately detecting the dissipation rate and (ii) indirect estimates of dissipation rate retrieved via the TKE budget equation from atmospheric measurements of other components of the TKE budget. The proposed formulation of dissipation rate will be of use in any turbulence-closure models employing the TKE budget equation and in problems requiring precise knowledge of the high-frequency part of turbulence spectra in atmospheric chemistry, aerosol science, and microphysics of clouds.

Design and Development of an Experimental Apparatus for Hardware-In-The-Loop Testing of Solar Assisted Heat Pump Systems

2021 ◽  
Author(s):  
George Benzion van Arnold ◽  
Weimin Wang
Keyword(s):  
Heat Pump ◽  
Hot Water ◽  
Water Withdrawal ◽  
Water Tank ◽  
Flow Paths ◽  
Domestic Hot Water ◽  
Labview Software ◽  
Experimental Apparatus ◽  
Hardware In Loop ◽  
Operational Modes

Abstract This paper presents an experimental apparatus designed and built to facilitate the study of solar-assisted heat pump (SAHP) systems using the hardware-in-loop methodology. The apparatus includes an 11.6kW capacity water-to-water heat pump, a 409L thermal storage tank, a 288L domestic hot water tank, two variable speed circulation pumps, and emulation hardware representing solar collectors and conditioned building space. A complex network of piping and electronic diverting valves is used to create various energy flow paths to support fifteen different operational modes for space heating, space cooling, domestic hot water generation, and energy storage charging. The apparatus is heavily instrumented for temperature and flow measurement. Controls and data acquisition are predominantly managed using National Instruments hardware and LabVIEW software. The experimental apparatus has been installed, commissioned, and tested. The basic functionality of control and operation has been verified through testing four different operational modes and domestic hot water withdrawal emulation. The experimental apparatus can be used not only as a platform for research on a multifunctional indirect expansion SAHP system, but also allow for similar testing of less-complex related SAHP configurations.

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