Mass Loading Effects on Turbulence Modulation by Particle Clustering in Dilute and Moderately Dilute Channel Flows

2015 ◽  
Vol 137 (11) ◽  
Author(s):  
Jesse Capecelatro ◽  
Olivier Desjardins
Keyword(s):  
Carrier Phase ◽  
Volume Fraction ◽  
Flow Direction ◽  
Channel Flows ◽  
Wall Region ◽  
Mass Loading ◽  
Mean Flow ◽  
Particle Clustering ◽  
Significant Volume ◽  
The Mean

Wall-bounded particle-laden flows exhibit a variety of interesting phenomena that can greatly impact the underlying carrier-phase turbulence in practical systems. This work aims at investigating the effects of particle clustering on the carrier-phase turbulence in both dilute and moderately dilute channel flows via highly resolved Euler–Lagrange simulations. It is shown that the fluid turbulence departs significantly from the initially fully developed turbulent flow at moderate concentrations. In particular, the gas velocity retains a viscous sublayer at higher values of mass loading, but displays a strongly reduced boundary layer thickness and a flatter velocity profile compared to the dilute case. Furthermore, the flow orientation with respect to gravity is found to significantly impact the multiphase dynamics. Particles showed a preference to be in the near-wall region with significant volume fraction fluctuations when gravity opposed the mean flow direction, while particles accumulated at the channel center with less significant volume fraction fluctuations for flows with gravity aligned with the mean flow direction.

Turbulence Modulation by Particle Clustering in Dilute and Moderately Dilute Channel Flows

2014 ◽  
Author(s):  
Jesse Capecelatro ◽  
Olivier Desjardins
Keyword(s):  
Carrier Phase ◽  
Flow Direction ◽  
Channel Flows ◽  
Channel Height ◽  
Spontaneous Generation ◽  
Mean Flow ◽  
Particle Clustering ◽  
Fluid Turbulence ◽  
Velocity Statistics ◽  
The Mean

Turbulent wall-bounded particle-laden flows exhibit a variety of interesting phenomena that can greatly impact the underlying carrier-phase turbulence. At sufficiently low particle concentrations and mass loadings, it is well established that inertial particles will accumulate in regions of high strain and avoid regions of high vorticity. At larger concentrations and mass loadings, intimate coupling between the phases may lead to flow instabilities, resulting in the spontaneous generation of dense clusters that can completely reorganize the structure of the underlying fluid turbulence. This work aims at investigating the effect of particle clustering on the carrier-phase turbulence in both dilute and moderately-dilute channel flows with a friction Reynolds number Reτ=630 using highly-resolved Euler-Lagrange simulations. To study the effect of gravity on cluster dynamics, simulations are conducted with gravity aligned in the mean flow direction, as well as gravity opposing the mean flow direction (i.e., a riser configuration). Particle segregation and velocity statistics are compared for each case. It is shown that the fluid turbulence departs significantly from the initially fully-developed turbulent flow when subject to a moderately dilute suspension of particles. In the denser channel flows, the gas velocity retains a viscous sublayer, but displays a strongly reduced boundary layer thickness and a flatter velocity profile compared to the unladen and dilute flows, leading to larger friction velocity. The particle concentration profile along the channel height is not found to be modified greatly by the increased particle loading, but is found to depend strongly on the orientation of gravity.

scholarly journals Generation of Reverse Meniscus Flow by Applying An Electromagnetic Brake

2021 ◽  
Author(s):  
Alexander Vakhrushev ◽  
Abdellah Kharicha ◽  
Ebrahim Karimi-Sibaki ◽  
Menghuai Wu ◽  
Andreas Ludwig ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Lorentz Force ◽  
Applied Magnetic Field ◽  
Numerical Study ◽  
Flow Direction ◽  
Experimental Studies ◽  
Submerged Entry Nozzle ◽  
Mean Flow ◽  
Slab Caster ◽  
The Mean

AbstractA numerical study is presented that deals with the flow in the mold of a continuous slab caster under the influence of a DC magnetic field (electromagnetic brakes (EMBrs)). The arrangement and geometry investigated here is based on a series of previous experimental studies carried out at the mini-LIMMCAST facility at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR). The magnetic field models a ruler-type EMBr and is installed in the region of the ports of the submerged entry nozzle (SEN). The current article considers magnet field strengths up to 441 mT, corresponding to a Hartmann number of about 600, and takes the electrical conductivity of the solidified shell into account. The numerical model of the turbulent flow under the applied magnetic field is implemented using the open-source CFD package OpenFOAM®. Our numerical results reveal that a growing magnitude of the applied magnetic field may cause a reversal of the flow direction at the meniscus surface, which is related the formation of a “multiroll” flow pattern in the mold. This phenomenon can be explained as a classical magnetohydrodynamics (MHD) effect: (1) the closure of the induced electric current results not primarily in a braking Lorentz force inside the jet but in an acceleration in regions of previously weak velocities, which initiates the formation of an opposite vortex (OV) close to the mean jet; (2) this vortex develops in size at the expense of the main vortex until it reaches the meniscus surface, where it becomes clearly visible. We also show that an acceleration of the meniscus flow must be expected when the applied magnetic field is smaller than a critical value. This acceleration is due to the transfer of kinetic energy from smaller turbulent structures into the mean flow. A further increase in the EMBr intensity leads to the expected damping of the mean flow and, consequently, to a reduction in the size of the upper roll. These investigations show that the Lorentz force cannot be reduced to a simple damping effect; depending on the field strength, its action is found to be topologically complex.

Effects of Pin Shape and Array Orientation on Heat Transfer and Pressure Loss in Pin Fin Arrays

1984 ◽  
Vol 106 (1) ◽  
pp. 252-257 ◽  
Author(s):  
D. E. Metzger ◽  
C. S. Fan ◽  
S. W. Haley
Keyword(s):  
Heat Transfer ◽  
Cross Section ◽  
Pressure Loss ◽  
Flow Direction ◽  
Circular Cross Section ◽  
Cycle Performance ◽  
Mean Flow ◽  
Pin Fin ◽  
The Mean ◽  
Cooling Air

Modern high-performance gas turbine engines operate at high turbine inlet temperatures and require internal convection cooling of many of the components exposed to the hot gas flow. Cooling air is supplied from the engine compressor at a cost to cycle performance and a design goal is to provide necessary cooling with the minimum required cooling air flow. In conjunction with this objective, two families of pin fin array geometries which have potential for improving airfoil internal cooling performance were studied experimentally. One family utilizes pins of a circular cross section with various orientations of the array with respect to the mean flow direction. The second family utilizes pins with an oblong cross section with various pin orientations with respect to the mean flow direction. Both heat transfer and pressure loss characteristics are presented. The results indicate that the use of circular pins with array orientation between staggered and inline can in some cases increase heat transfer while decreasing pressure loss. The use of elongated pins increases heat transfer, but at a high cost of increased pressure loss. In conjunction with the present measurements, previously published results were reexamined in order to estimate the magnitude of heat transfer coefficients on the pin surfaces relative to those of the endwall surfaces. The estimate indicates that the pin surface coefficients are approximately double the endwall values.

Measurement of the Mean Flow Field in a Smooth Rotating Channel With Coriolis and Buoyancy Effects

2017 ◽  
Author(s):  
Ruquan You ◽  
Haiwang Li ◽  
Zhi Tao ◽  
Kuan Wei
Keyword(s):  
Flow Field ◽  
Coriolis Force ◽  
Indium Tin Oxide ◽  
Buoyancy Force ◽  
Flow Direction ◽  
Density Ratio ◽  
Mean Flow ◽  
The Mean ◽  
Static Conditions ◽  
Rotating Channel

The mean flow field in a smooth rotating channel was measured by particle image velocimetry under the effect of buoyancy force. In the experiments, the Reynolds number, based on the channel hydraulic diameter (D) and the bulk mean velocity (Um), is 10000, and the rotation numbers are 0, 0.13, 0.26, 0.39, 0.52, respectively. The four channel walls are heated with Indium Tin Oxide (ITO) heater glass, making the density ratio (d.r.) about 0.1 and the maximum value of buoyancy number up to 0.27. The mean flow field was simulated on a 3D reconstruction at the position of 3.5<X/D<6.5, where X is along the mean flow direction. The effect of Coriolis force and buoyancy force on the mean flow was taken into consideration in the current work. The results show that the Coriolis force pushes the mean flow to the trailing side, making the asymmetry of the mean flow with that in the static conditions. On the leading surface, due to the effect of buoyancy force, the mean flow field changes considerably. Comparing with the case without buoyancy force, separated flow was captured by PIV on the leading side in the case with buoyancy force. More details of the flow field will be presented in this work.

Turbulent Wall-Pressure Fluctuations: A New Model for Off-Axis Cross-Spectral Density

1997 ◽  
Vol 119 (2) ◽  
pp. 277-280 ◽  
Author(s):  
B. A. Singer
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Spectral Density ◽  
Flow Direction ◽  
Wall Pressure ◽  
Mean Flow ◽  
New Approach ◽  
Cross Spectral Density ◽  
The Mean ◽  
The Cross

Models for the distribution of the wall-pressure under a turbulent boundary layer often estimate the coherence of the cross-spectral density in terms of a product of two coherence functions. One such function describes the coherence as a function of separation distance in the mean-flow direction, the other function describes the coherence in the cross-stream direction. Analysis of data from a large-eddy simulation of a turbulent boundary layer reveals that this approximation dramatically underpredicts the coherence for separation directions that are neither aligned with nor perpendicular to the mean-flow direction. These models fail even when the coherence functions in the directions parallel and perpendicular to the mean flow are known exactly. A new approach for combining the parallel and perpendicular coherence functions is presented. The new approach results in vastly improved approximations for the coherence.

Experimental Investigation of a Tandem Cylinder System With a Yawed Upstream Cylinder

2011 ◽  
Author(s):  
Stephen J. Wilkins ◽  
Joseph W. Hall
Keyword(s):  
Experimental Investigation ◽  
Flow Field ◽  
Unsteady Flow ◽  
Surface Pressure ◽  
Vortex Shedding ◽  
Flow Direction ◽  
Pressure Fluctuations ◽  
Mean Flow ◽  
The Mean ◽  
Velocity Spectra

The unsteady flow field produced by a tandem cylinder system with the upstream cylinder yawed to the mean flow direction is investigated for upstream cylinder yaw angles from α = 60° to α = 90°. Multi-point fluctuating surface pressure and hotwire measurements were conducted at various spanwise positions on both the upstream and downstream cylinders. The results indicate that yawing the front cylinder to the mean flow direction causes the pressure and velocity spectra on the upstream and downstream cylinders to become more broadband than for a regular tandem cylinder system, and reduces the magnitude of the peak associated with the vortex-shedding. However, span-wise correlation and coherence measurements indicate that the vortex-shedding is still present and was being obscured by the enhanced three-dimensionality that the upstream yawed cylinder caused and was still present and correlated from front to back, at least for the larger yaw angles investigated. When the cylinder was yawed to α = 60°, the pressure fluctuations became extremely broadband and exhibited shorter spanwise correlation.

Effect of Number of Roughing Passes on the Dynamic Transformation of Austenite during Simulated Plate Rolling

2018 ◽  
Vol 941 ◽  
pp. 717-722
Author(s):  
Samuel F. Rodrigues ◽  
Fulvio Siciliano ◽  
Clodualdo Aranas Jr. ◽  
Gedeon S. Reis ◽  
Brian J. Allen ◽  
...  
Keyword(s):  
Grain Size ◽  
Volume Fraction ◽  
Austenite Phase ◽  
Mean Flow ◽  
Grain Sizes ◽  
Dynamic Transformation ◽  
Plate Rolling ◽  
Forward Transformation ◽  
The Mean ◽  
Rough Rolling

When austenite is deformed within the austenite phase field, it partially transforms dynamically into ferrite. Here, plate rolling simulations were carried out on an X70 steel using rough rolling passes of 0.4 strain each. The influence of the number of roughing passes on the grain size and volume fraction of induced ferrite was determined. Up to three roughing passes applied at 1100 °C followed by 5 finishing passes at 900 °C were employed. The sample microstructures were analysed by means of metallographic techniques. Both the critical strain to the onset of dynamic transformation as well as the grain size decreased with pass number during the roughing simulations. For the finishing passes, the mean flow stresses (MFS`s) applicable to each schedule decreased when a higher number of roughing passes was applied. The volume fraction of dynamically formed ferrite retained after simulated rolling increased with the roughing pass number. This is ascribed to the increased amount of ferrite retransformed into austenite and the finer grain sizes produced during roughing. The forward transformation is considered to occur displacively while the retransformation into austenite during holding takes place by a diffusional mechanism. This indicates that both dynamic transformation (DT) and dynamic recrystallization were taking place during straining.

Measurements with a pulsed-wire and a hot-wire anemometer in the highly turbulent wake of a normal flat plate

1976 ◽  
Vol 77 (3) ◽  
pp. 473-497 ◽  
Author(s):  
L. J. S. Bradbury
Keyword(s):  
Turbulent Flow ◽  
Flat Plate ◽  
Flow Direction ◽  
Operating Conditions ◽  
Turbulent Intensity ◽  
Hot Wire ◽  
Mean Flow ◽  
Mean Velocity ◽  
The Mean ◽  
Better Than

This paper describes an investigation into the response of both the pulsed-wire anemometer and the hot-wire anemometer in a highly turbulent flow. The first part of the paper is concerned with a theoretical study of some aspects of the response of these instruments in a highly turbulent flow. It is shown that, under normal operating conditions, the pulsed-wire anemometer should give mean velocity and longitudinal turbulent intensity estimates to an accuracy of better than 10% without any restriction on turbulence level. However, to attain this accuracy in measurements of turbulent intensities normal to the mean flow direction, there is a lower limit on the turbulent intensity of about 50%. An analysis is then carried out of the behaviour of the hot-wire anemometer in a highly turbulent flow. It is found that the large errors that are known to develop are very sensitive to the precise structure of the turbulence, so that even qualitative use of hot-wire data in such flows is not feasible. Some brief comments on the possibility of improving the accuracy of the hot-wire anemometer are then given.The second half of the paper describes some comparative measurements in the highly turbulent flow immediately downstream of a normal flat plate. It is shown that, although it is not possible to interpret the hot-wire results on their own, it is possible to calculate the hot-wire response with a surprising degree of accuracy using the results from the pulsed-wire anemometer. This provides a rather indirect but none the less welcome check on the accuracy of the pulsed-wire results, which, in this very highly turbulent flow, have a certain interest in their own right.

Fully coupled resonant-triad interactions in a free shear layer

1994 ◽  
Vol 278 ◽  
pp. 101-121 ◽  
Author(s):  
R. Mallier ◽  
S. A. Maslowe
Keyword(s):  
Flow Direction ◽  
Mixing Layer ◽  
Adverse Pressure Gradient ◽  
Critical Layer ◽  
Free Shear Layer ◽  
Mean Flow ◽  
Weakly Nonlinear ◽  
Initial Interaction ◽  
The Mean ◽  
Fully Coupled

We report the results of an investigation of the weakly nonlinear evolution of a triad of waves, each slightly amplified on a linear basis, that are superimposed on a tanh y mixing layer. The triad consists of a plane wave and a pair of oblique modes that act as a subharmonic of order 1/2. The oblique modes are inclined at approximately ±60°. to the mean flow direction and because the resonance conditions are satisfied exactly the analysis is entirely self-consistent as an asymptotic theory. The nonlinearity first occurs within the critical layer and the initial interaction is of the parametric resonance type. This produces faster than exponential growth of the oblique waves, behaviour observed recently in the experiments of Corke & Kusek (1993). The critical-layer dynamics lead subsequently to coupled integro-differential equations governing the amplitude evolution and, as first shown in related work by Goldstein & Lee (1992) on boundary layers in an adverse pressure gradient, these equations develop singularities in a finite time.

Further space-time correlations of velocity in a turbulent boundary layer

1958 ◽  
Vol 3 (4) ◽  
pp. 344-356 ◽  
Author(s):  
A. J. Favre ◽  
J. J. Gaviglio ◽  
R. J. Dumas
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Large Scale ◽  
Flow Direction ◽  
Space Time ◽  
Mean Flow ◽  
Taylor’S Hypothesis ◽  
Time Correlations ◽  
The Mean ◽  
Hot Wires

This paper describes the results of further experimental investigation of the turbulent boundary layer with zero pressure gradient. Measurements of autocorrelation and of space-time double correlation have been made respectively with single hot-wires and with two hot-wires with the separation vector in any direction. Space-time correlations reach a maximum for some optimum delay. In the case of two points set on a line orthogonal to the plate, the optimum delay Ti is not zero. In the general case it is equal to the corresponding delay Ti, increased by compensating delay for translation with the mean flow. Taylor's hypothesis may be applied to the boundary layer at distances from the wall greater than 3% of the layer thickness. Space-time isocorrelation surfaces obtained with optimum delay have a large aspect ratio in the mean flow direction, even if they are relative to a point close to the wall (0·03δ); the correlations along the mean flow then retain high values on account of the large scale of the turbulence.

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