Measurement of Turbulent Mass Mixing Caused by a Particle Wake

2003 ◽  
Author(s):  
Toru Koso ◽  
Eiji Koyama ◽  
Takayuki Mikamoto
Keyword(s):  
Reynolds Number ◽  
Diffusion Coefficient ◽  
Turbulent Mixing ◽  
Large Scale ◽  
Molecular Diffusion ◽  
Mixing Time ◽  
Measured Concentration ◽  
Turbulent Diffusion Coefficient ◽  
Number Range ◽  
Photochromic Dye

When a particle moves in a fluid, the fluid is disturbed by the particle and the fluid mass is mixed. This phenomenon is commonly observed in particle-laden flows and dispersed bubble flows. This mass mixing can be composed of two mechanisms. One is the mass transfer by convective flows that are induced by the reaction of the particle drag and the other is the turbulent mass mixing in the turbulent wake of the particle. The effect of the former one can be evaluated using the previous studies on the particle drag. However, the effect of the turbulent mixing is little understood. The turbulent mixing caused by a particle wake is investigated by visualization and noninvasive concentration measurement using a photochromic dye. A sphere brass particle of 5mm in diameter is dropped in kerosene filled in a vertical pipe and the mixing of dye is visualized. The photochromic dye, which is activated by an ultraviolet light, keeps its color in a few minutes after the activation. A part of the fluid is activated without disturbances and is subjected to the mixing by the particle wake. The visualized dye patterns indicate the dye is mixed isotropically by large-scale vortex motions when the particle sheds the vortices. Furthermore, the photochromic concentration measuring (PCM) technique is developed to obtain the concentration of the mixed dye. This PCM technique is based on the Lambert-Beer’s law for light adsorption and provides the average dye concentration along the light path. The measured concentration distribution shows rather isotropic mixing in longitudinal direction. The turbulent diffusion coefficient (TDC) is calculated from the temporal changes in the measured concentration distributions. The evaluated TDC shows strong time-dependency, which is attributed to the change in scale and strength of wake vortices. The TDC is about 104 times larger than the molecular diffusion coefficient at its maximum. The effect of particle Reynolds number on the turbulent mixing is also investigated for the Reynolds number range from 263 to 3290. The observed mixing patterns show a drastic change at the critical Reynolds number on the vortex shedding from the particle. The Reynolds number dependency on the non-dimensional TDC and mixing time are discussed.

Mixing of Matter by a Falling Spherical Particle in a Still Liquid

2015 ◽  
Author(s):  
Toru Koso
Keyword(s):  
Reynolds Number ◽  
Spherical Particle ◽  
Mixing Time ◽  
Reynolds Numbers ◽  
Fluid Viscosity ◽  
Liquid Viscosity ◽  
Turbulent Diffusion Coefficient ◽  
Number Range ◽  
Particle Reynolds Number ◽  
Photochromic Dye

The mixing of liquid mass caused by a spherical solid particle falling in a still liquid in a pipe was investigated by visualization and noninvasive concentration measurement using a photochromic dye. A spherical particle with diameter of 4.76 mm was dropped in a kerosene-paraffin mixture liquid with a photochromic dye. The photochromic dye was activated by an ultraviolet light and was subjected to the mixing by the particle wake. The falling velocity of particle was changed by using 8 different densities of particle. The effect of the particle Reynolds number on the mixing was investigated for the Reynolds number range from 10 to 2490. The effect of liquid viscosity on the mixing time was also investigated using two liquids having different viscosity. The visualized dye patterns indicated the mixing process depended strongly on the particle Reynolds number. For the Reynolds numbers higher than 300, the particle shed the vortices behind the particle and the dye was mixed isotropically by large-scale vortices. For the Reynolds numbers lower than 300, the dye was drawn straightly by a laminar wake of the particle. The concentration of the mixed dye was measured using the photochromic concentration measuring (PCM) technique to discuss the mass mixing quantitatively. The turbulent diffusion coefficient (TDC) was evaluated for the cases the dye was mixed by the vortices. It was found that the evaluated TDCs showed strong time-dependency, which was attributed to the change in scale and whirling velocity of wake vortices. The maximum TDC depended on the falling velocity regardless of the fluid viscosity. The mixing time depended strongly on the liquid viscosity. The mixing time of the TDC was suggested to be governed by the viscous decay time and expanding time of vortices in the pipe. The amount of dye drift was evaluated for the cases the particle wake was laminar. It was found that the dye drift increased sharply just after the particle passing and then saturated. The final dye drift increased gradually with increasing Reynolds number.

A numerical study of the transition of jet diffusion flames

1990 ◽  
Vol 431 (1882) ◽  
pp. 301-314 ◽  
Keyword(s):  
Reynolds Number ◽  
Diffusion Coefficient ◽  
Large Scale ◽  
Numerical Study ◽  
Small Scale ◽  
Surface Model ◽  
Flame Surface ◽  
Transition Mechanism ◽  
Air Stream ◽  
Scale Fluctuation

A numerical study on the transition from laminar to turbulent of two-dimensional fuel jet flames developed in a co-flowing air stream was made by adopting the flame surface model of infinite chemical reaction rate and unit Lewis number. The time dependent compressible Navier–Stokes equation was solved numerically with the equation for coupling function by using a finite difference method. The temperature-dependence of viscosity and diffusion coefficient were taken into account so as to study effects of increases of these coefficients on the transition. The numerical calculation was done for the case when methane is injected into a co-flowing air stream with variable injection Reynolds number up to 2500. When the Reynolds number was smaller than 1000 the flame, as well as the flow, remained laminar in the calculated domain. As the Reynolds number was increased above this value, a transition point appeared along the flame, downstream of which the flame and flow began to fluctuate. Two kinds of fluctuations were observed, a small scale fluctuation near the jet axis and a large scale fluctuation outside the flame surface, both of the same origin, due to the Kelvin–Helmholtz instability. The radial distributions of density and transport coefficients were found to play dominant roles in this instability, and hence in the transition mechanism. The decreased density in the flame accelerated the instability, while the increase in viscosity had a stabilizing effect. However, the most important effect was the increase in diffusion coefficient. The increase shifted the flame surface, where the large density decrease occurs, outside the shear layer of the jet and produced a thick viscous layer surrounding the jet which effectively suppressed the instability.

Aeroacoustic properties of supersonic elliptic jets

1999 ◽  
Vol 395 ◽  
pp. 1-28 ◽  
Author(s):  
KEVIN W. KINZIE ◽  
DENNIS K. McLAUGHLIN
Keyword(s):  
Reynolds Number ◽  
Large Scale ◽  
Near Field ◽  
Operating Conditions ◽  
Acoustic Properties ◽  
Instability Wave ◽  
Hot Wire ◽  
Number Range ◽  
Circular Jets ◽  
Exit Mach Number

The aerodynamic and acoustic properties of supersonic elliptic and circular jets are experimentally investigated. The jets are perfectly expanded with an exit Mach number of approximately 1.5 and are operated in the Reynolds number range of 25 000 to 50 000. The reduced Reynolds number facilitates the use of conventional hot-wire anemometry and a glow discharge excitation technique which preferentially excites the varicose or flapping modes in the jets. In order to simulate the high-velocity and low-density effects of heated jets, helium is mixed with the air jets. This allows the large-scale structures in the jet shear layer to achieve a high enough convective velocity to radiate noise through the Mach wave emission process.Experiments in the present work focus on comparisons between the cold and simulated heated jet conditions and on the beneficial aeroacoustic properties of the elliptic jet. When helium is added to the jet, the instability wave phase velocity is found to approach or exceed the ambient sound speed. The radiated noise is also louder and directed at a higher angle from the jet axis. In addition, near-field hot-wire spectra are found to match the far-field acoustic spectra only for the helium/air mixture case. These results demonstrate that there are significant differences between unheated and heated asymmetric jets in the Mach 1.5 speed range, many of which have been found previously for circular jets. The elliptic jet was also found to radiate less noise than the round jet at comparable operating conditions.

A strategy for large-scale scalar advection in large eddy simulations that use the linear eddy sub-grid mixing model

2018 ◽  
Vol 28 (10) ◽  
pp. 2463-2479 ◽  
Author(s):  
Salman Arshad ◽  
Bo Kong ◽  
Alan Kerstein ◽  
Michael Oevermann
Keyword(s):  
Turbulent Mixing ◽  
Large Scale ◽  
Molecular Diffusion ◽  
Passive Scalar ◽  
Mixing Model ◽  
Large Eddy Simulations ◽  
High Flux ◽  
Scalar Mixing ◽  
Content Type ◽  
Large Eddy

PurposeThe purpose of this numerical work is to present and test a new approach for large-scale scalar advection (splicing) in large eddy simulations (LES) that use the linear eddy sub-grid mixing model (LEM) called the LES-LEM.Design/methodology/approachThe new splicing strategy is based on an ordered flux of spliced LEM segments. The principle is that low-flux segments have less momentum than high-flux segments and, therefore, are displaced less than high-flux segments. This strategy affects the order of both inflowing and outflowing LEM segments of an LES cell. The new splicing approach is implemented in a pressure-based fluid solver and tested by simulation of passive scalar transport in a co-flowing turbulent rectangular jet, instead of combustion simulation, to perform an isolated investigation of splicing. Comparison of the new splicing with a previous splicing approach is also done.FindingsThe simulation results show that the velocity statistics and passive scalar mixing are correctly predicted using the new splicing approach for the LES-LEM. It is argued that modeling of large-scale advection in the LES-LEM via splicing is reasonable, and the new splicing approach potentially captures the physics better than the old approach. The standard LES sub-grid mixing models do not represent turbulent mixing in a proper way because they do not adequately represent molecular diffusion processes and counter gradient effects. Scalar mixing in turbulent flow consists of two different processes, i.e. turbulent mixing that increases the interface between unmixed species and molecular diffusion. It is crucial to model these two processes individually at their respective time scales. The LEM explicitly includes both of these processes and has been used successfully as a sub-grid scalar mixing model (McMurtry et al., 1992; Sone and Menon, 2003). Here, the turbulent mixing capabilities of the LES-LEM with a modified splicing treatment are examined.Originality/valueThe splicing strategy proposed for the LES-LEM is original and has not been investigated before. Also, it is the first LES-LEM implementation using unstructured grids.

scholarly journals Coefficient of heterogeneity in turbulent mixing zone

2000 ◽  
Vol 18 (2) ◽  
pp. 207-212 ◽  
Author(s):  
A.S. KOZLOVSKIH ◽  
D.V. NEUVAZHAYEV
Keyword(s):  
Turbulent Mixing ◽  
Molecular Diffusion ◽  
Reynolds Numbers ◽  
Mixing Zone ◽  
Turbulent Diffusion Coefficient ◽  
Dissipative Term ◽  
Developed Turbulence ◽  
Self Similar Solution ◽  
Self Similar ◽  
Good Agreement

The paper considers the equation for heterogeneity coefficient within the turbulent mixing area in the approximation of big Reynolds numbers and small Mach numbers. A mechanism is studied of the heterogeneity coefficient dissipation due to molecular diffusion. The Kolmogorov's hypothesis on developed turbulence is used to calculate a dissipative term. The model presented allows us to take into account the heterogeneity degree in LV- and KE-models of turbulent mixing. A system of equations allowing us to calculate directly the heterogeneity degree is derived for the case of the LV-model with the turbulent diffusion coefficient which is constant over the turbulent mixing area. A self-similar solution is derived for the heterogeneity coefficient which is in good agreement with the results of experiments and direct numerical simulations. The heterogeneity coefficient averaged over the mixing area is shown to depend weakly on the density drop between the mixing materials. Thus, it is kH = 0.25 at the drop n = 1–3, and at the drop n = 20 − kH = 0.23.

scholarly journals Some peculiarities of turbulent mixing growth and perturbations at hydrodynamic instabilities

2013 ◽  
Vol 371 (2003) ◽  
pp. 20120291 ◽  
Author(s):  
N. V. Nevmerzhitskiy
Keyword(s):  
Shock Wave ◽  
Reynolds Number ◽  
Mach Number ◽  
Turbulent Mixing ◽  
Large Scale ◽  
Hydrodynamic Instabilities ◽  
Mixing Zone ◽  
Gaseous Media ◽  
Experimental Works ◽  
Atwood Number

The author presents a review of some experimental works devoted to the research of evolution of large-scale perturbations and turbulent mixing (TM) in liquid and gaseous media during the growth of hydrodynamic instabilities. In particular, it is shown that growth of perturbations and TM in gases is sensitive to the Mach number of shock wave; character of gas front penetration into liquid is not changed as the Reynolds number of flow increases from 5×10 5 to 10 7 ; and change of the Atwood number sign from positive to negative causes stopping of gas front penetration into liquid, but mixing zone width is expanded under inertia.

scholarly journals Effect of Reynolds number on a normal shock wave-transitional boundary-layer interaction over a curved surface

2019 ◽  
Vol 60 (12) ◽  
Author(s):  
A. Coschignano ◽  
N. Atkins ◽  
H. Babinsky ◽  
J. Serna
Keyword(s):  
Boundary Layer ◽  
Shock Wave ◽  
Reynolds Number ◽  
Large Scale ◽  
Curved Surface ◽  
Normal Shock ◽  
Pressure Gradients ◽  
Number Range ◽  
Normal Shock Wave ◽  
Transition Mechanism

Abstract The interaction between a normal shock wave and a boundary layer is investigated over a curved surface for a Reynolds number range, based on boundary-layer growing length x, of $$0.44\times 10^6\le \text {Re}_x\le 1.09\times 10^6$$0.44×106≤Rex≤1.09×106. The upstream boundary layer develops around the leading edge of the model before encountering a $$M$$M$$\sim $$∼1.4 normal shock. This is followed by adverse pressure gradients. The shock position and strength are kept constant as $$\text {Re}$$Re is progressively varied. Infra-red thermography is used to determine the nature of the upstream boundary layer. Across the $$\text {Re}$$Re range, this is observed to vary from fully laminar to fully turbulent across the entire span. Regardless of the boundary-layer state, the interaction remains benign in nature, without large scale shock-induced separation or unsteadiness. Schlieren images show a pronounced oblique wave developing upstream of the main shock for the laminar cases, this is believed to correspond to the separation and subsequent transition of the laminar shear layer. Downstream of the shock, in the presence of adverse pressure gradients, the boundary-layer growth rate is inversely proportional to $$\text {Re}$$Re. Nonetheless, across the entire range of inflow conditions the boundary layer recovers quickly to a healthy turbulent boundary layer. This suggests the upstream boundary-layer state, and its transition mechanism, to have little effect on the outcome of its interaction with a normal shock wave. Graphic abstract

Aerodynamics of a Covered Trailing Edge Vane: Effects of Blowing Rate, Reynolds Number, and External Turbulence

2009 ◽  
Author(s):  
I. Jaswal ◽  
E. Erickson ◽  
F. E. Ames
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Loss ◽  
Total Pressure ◽  
Large Scale ◽  
Total Pressure Loss ◽  
Internal Cooling ◽  
Trailing Edge ◽  
Number Range ◽  
Exit Survey

A covered trailing edge vane was developed by opening a fully loaded incompressible vane to accept an internal flow passage. The internal passage was filled with a high solidity internal cooling scheme. Exit survey measurements were acquired downstream from a large scale low speed linear cascade test section using a 5-hole cone probe at 1/4 axial chord downstream from the vane trailing edge. Exit survey measurements detailed total pressure loss, turning angle and secondary velocities. Exit survey measurements were conducted across a range of blowing rates (25% to 150% design), Reynolds numbers (500,000, 1,000,000 and 2,000,000) and turbulence levels [low (0.7%), grid (8.5%) and aero-combustor (13.5%)]. Losses for a thickened baseline vane (no blowing, same profile) were also acquired across the Reynolds number range and turbulence conditions. Vane midspan pressure and heat transfer distributions were acquired to help document the state of the boundary layers developing on the vane surface. Measurements are presented in terms of total pressure loss contours with secondary velocities and spanwise distributions of circumferentially averaged losses and turning angles. Overall loss values have been compared with measurements taken using the original base vane and a conventional gill slot vane. Comparisons between the base vane and the covered base vane show an incremental increase in total pressure losses of about 0.95% due the thicker trailing edge. Comparisons between the gill slot (pressure side cutback) and the covered trailing edge vane at comparable flow conditions show a much smaller loss penalty. Loss data for the gill slot vane suggest that both separation off the gill slot lip and the discharge of low momentum fluid are responsible for significant incremental losses above the base vane. The covered trailing edge vane has no additional surface with separation losses which penalizes the aerodynamics. Heat transfer rates for the internal cooling scheme are documented in a separate paper [1].

scholarly journals The Development of a New Experimental Facility for the Simulation of Civil Aircraft Engine Air-Intakes at High Reynolds Number

1999 ◽  
Author(s):  
Jeremy D. Murgatroyd
Keyword(s):  
Reynolds Number ◽  
Wind Tunnel ◽  
Large Scale ◽  
Reynolds Numbers ◽  
Full Scale ◽  
Boundary Layer Transition ◽  
Layer Transition ◽  
Number Range ◽  
Civil Aircraft ◽  
High Reynolds

A unique wind tunnel based method for simulating the engine air intakes of civil aircraft at high Reynolds numbers is described. The method combines a newly developed test rig with the 8ft × 8ft subsonic / supersonic wind tunnel at DERA Bedford. Commissioning tests of the rig took place in November 1997. Previous studies have shown that Reynolds number can have a significant effect on intake flow characteristics in certain flight regimes. One such regime is high incidence manoeuvre, such as the emergency pull-up, where engine performance may be seriously degraded by distorted airflow from the intake cowl. Common methods for artificially simulating increased Reynolds number, such as boundary layer transition fixing, are not practical for intake model tests due to the widely varying position of the attachment line on the cowl. Hence, for intake tests, there can be significant gains from testing at the highest available Reynolds number, preferably approaching the full-scale value. The new DERA facility offers accurate and cost effective performance assessment of large-scale intake models at near full-scale Reynolds numbers, across a Mach number range of 0.37 to 0.7. Throat choked mass flows can be achieved at Reynolds numbers up to approximately 11 million based on a model highlight diameter of 0.4 m. Model incidence can be varied between −10° and +30° (with and without sideslip). It is believed that this range of test conditions cannot be matched elsewhere in the world, without the additional risk and expense imposed by full-scale flight testing. This paper details the conceptual design of the rig and the principles behind its operation. Special mention is made of the innovative use of theoretically based methods to calibrate the rig in the absence of experimental equipment with sufficient flow capacity. These theoretical methods significantly reduced the development time and cost of the rig.

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