Mobility Deposition Effect of Aerosol Particles in the Boundary Layer

2013 ◽  
Vol 300-301 ◽  
pp. 924-927
Author(s):  
Ming Chi Chiou ◽  
Wen Zong Hsu
Keyword(s):  
Boundary Layer ◽  
Particle Deposition ◽  
Particle Concentration ◽  
Fluid Motion ◽  
Viscous Sublayer ◽  
Boundary Layer Flows ◽  
Random Surface ◽  
Surface Renewal ◽  
Developed Turbulence ◽  
Deposition Effect

The particle concentration and convection velocity profile has been obtained by the adaptation of the random surface renewal model to the particle continuity and momentum equations of the nonisothermal turbulence boundary-layer flows In general, the investigations of particle deposition mainly include incompressible fluid laden by spherical and dilute particles in the fully developed turbulence boundary layer flows. This means that the fluid motion is unaffected by the presence of the particles and that the collisions between particles can be neglected. the relative quiescent viscous sublayer, resulting in the increase in thermophoretic deposition with increased Prandtl number.

Investigation of Boundary Layer Flows Over a Flat Plate With Different-Size Transverse Square Grooves at s/w = 10

2007 ◽  
Author(s):  
Redha Wahidi ◽  
Walid Chakroun ◽  
Sami Al-Fahad
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
Skin Friction ◽  
Turbulence Intensity ◽  
Viscous Sublayer ◽  
Velocity Profiles ◽  
Boundary Layer Flows ◽  
Mean Velocity ◽  
Uncertainty Range ◽  
The Mean

Turbulent boundary layer flows over a flat plate with multiple transverse square grooves spaced 10 element widths apart were investigated. Mean velocity profiles, turbulence intensity profiles, and the distributions of the skin-friction coefficients (Cf) and the integral parameters are presented for two grooved walls. The two transverse square groove sizes investigated are 5mm and 2.5mm. Laser-Doppler Anemometer (LDA) was used for the mean velocity and turbulence intensity measurements. The skin-friction coefficient was determined from the gradient of the mean velocity profiles in the viscous sublayer. Distribution of Cf in the first grooved-wall case (5mm) shows that Cf overshoots downstream of the groove and then oscillates within the uncertainty range and never shows the expected undershoot in Cf. The same overshoot is seen in the second grooved-wall case (2.5mm), however, Cf continues to oscillate above the uncertainty range and never returns to the smooth-wall value. The mean velocity profiles clearly represent the behavior of Cf where a downward shift is seen in the Cf overshoot region and no upward shift is seen in these profiles. The results show that the smaller grooves exhibit larger effects on Cf, however, the boundary layer responses to these effects in a slower rate than to those of the larger grooves.

Low-Reynolds-Number Turbulent Boundary Layers

1981 ◽  
Vol 103 (4) ◽  
pp. 624-630 ◽  
Author(s):  
B. R. White
Keyword(s):  
Boundary Layer ◽  
Shape Factor ◽  
Reynolds Numbers ◽  
Viscous Sublayer ◽  
Factor H ◽  
Boundary Layer Flows ◽  
Viscous Effects ◽  
Boundary Layer Height ◽  
Wind Tunnel Data ◽  
Logarithmic Velocity Profile

This paper presents experimental wind-tunnel data that show the universal logarithmic velocity profile for zero-pressure-gradient turbulent boundary layer flows is valid for values of momentum-deficit Reynolds numbers Rθ as low as 600. However, for values of Rθ between 425 and 600, the von Ka´rma´n and additive constants vary and are shown to be functions of Rθ and shape factor H. Furthermore, the viscous sublayer in the range 425<Rθ<600 can no longer maintain its characteristically small size. It is forced to grow, due to viscous effects, into a super sublayer (6-9 percent of the boundary layer height) that greatly exceeds conventional predictions of sublayer heights.

A Theory for Fine Particle Deposition in Two-Dimensional Boundary Layer Flows and Application to Gas Turbines

1982 ◽  
Vol 104 (1) ◽  
pp. 69-76 ◽  
Author(s):  
M. Mengu¨turk ◽  
E. F. Sverdrup
Keyword(s):  
Boundary Layer ◽  
Gas Turbines ◽  
Particle Deposition ◽  
Fine Particles ◽  
Magnitude Estimate ◽  
Two Dimensional ◽  
Boundary Layer Flows ◽  
Order Of Magnitude ◽  
Dimensional Boundary ◽  
Layer Flow

A theory is presented to predict deposition rates of fine particles in two-dimensional compressible boundary layer flows. The mathematical model developed accounts for diffusion due to both molecular and turbulent fluctuations in the boundary layer flow. Particle inertia is taken into account in establishing the condition on particle flux near the surface. Gravitational settling and thermophoresis are not considered. The model assumes that the fraction of particles sticking upon arrival at the surface is known, and thus, treats it as a given parameter. The theory is compared with a number of pipe and cascade experiments, and a reasonable agreement is obtained. A detailed application of the model to a turbine is also presented. Various regimes of particle transport are identified, and the range of validity of the model is discussed. An order of magnitude estimate is obtained for the time the turbine stage can be operated without requiring cleaning.

scholarly journals Laboratory experiments on the dynamics of powder-snow avalanches in the run-out zone

1991 ◽  
Vol 37 (126) ◽  
pp. 281-295 ◽  
Author(s):  
Felix Hermann ◽  
Kolumban Hutter
Keyword(s):  
Boundary Layer ◽  
Laboratory Experiments ◽  
Particle Concentration ◽  
Dynamic Pressure ◽  
Considerable Reduction ◽  
Snow Avalanches ◽  
Boundary Layer Flows ◽  
Ensemble Averaging ◽  
Particle Sedimentation ◽  
Turbulence Effects

AbstractWe report on laboratory experiments on the motion of powder-snow avalanches along a bent chute. The avalanches are simulated as turbulent boundary-layer flows of polystyrene particles in still water along a chute consisting of a straight inclined part, a curved part and a second, possibly inclined, run-out zone. An ultrasonic measuring technique is used to determine mean particle speeds (via the Doppler shift of the reflected signal) and the particle concentration (via the attenuation of the echoes). By ensemble averaging, individual turbulence effects are eliminated. As measuring procedures,profileswere determined for particle velocity and density across the boundary layer; these were taken (i) for the avalanche tail along the entire track, i.e. in the steep part and the run-out zone, and (ii) for the avalanche head in the run-out zone below the kink in the terrain. Moreover,time sectionsof velocity and density (i.e. time series at fixed positions along a line through the boundary layer) were recorded and the particle mass deposited in the various zones of the track was measured.The analysis of the data reveals the following results: a concave change in the terrain topography acts as a very efficient mechanism for particle sedimentation, thus affecting particle concentration and velocity, and considerable reduction close to the ground, whereas the density is reduced throughout the depth, thus leading to a considerable reduction of dynamic pressure close to the ground and leaving it somewhat greater at higher altitudes. We conclude with practical considerations for the field glaciologist.

Particle Concentration Variation for Inflow Profiles in High Reynolds Number Turbulent Boundary Layer

2020 ◽  
Author(s):  
Mustafa M. Rahman ◽  
Ravi Samtaney
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Turbulent Flows ◽  
Particle Concentration ◽  
Solid Particles ◽  
Scale Model ◽  
Normal Velocity ◽  
Boundary Layer Flows ◽  
Ground Field ◽  
High Reynolds

Abstract Large-eddy simulations (LES) of incompressible turbulent boundary-layer flows can simulate a fundamental unsteady turbulent flow, including time-variant streamwise and wall-normal velocity as well as the near-wall locations of significant turbulence intensities. A typical illustration of turbulent flows with such high Reynolds numbers can be roughly approximated to atmospheric boundary-layer flows. To bypass the demanding mesh criteria of near-ground field and direct numerical simulations, we adopt a virtual-wall model with a stretched-vortex subgrid-scale model. We simulate the dynamics of solid particles in this wall-modeled LES approach toward incompressible flow. The particles considered are both charged and uncharged, and have a fixed concentration profile with no fluctuations at the inflow. An extended streamwise simulation domain is implemented as an alternative to rerunning the simulation with a turbulent inflow profile from the simulation of the previous downstream profile. By extending the streamwise domain, the fluctuation dynamics of the particles reach a steady state far downstream from the inflow. The streamwise and altitude variation of the particle parameters are compared for various particle-concentration inflow profiles. Furthermore, an estimate of the streamwise variation of parameters is also observed. This study is the first step towards enhancing our understanding of the particle dynamics in turbulent flows.

scholarly journals Laboratory experiments on the dynamics of powder-snow avalanches in the run-out zone

1991 ◽  
Vol 37 (126) ◽  
pp. 281-295 ◽  
Author(s):  
Felix Hermann ◽  
Kolumban Hutter
Keyword(s):  
Boundary Layer ◽  
Laboratory Experiments ◽  
Particle Concentration ◽  
Dynamic Pressure ◽  
Considerable Reduction ◽  
Snow Avalanches ◽  
Boundary Layer Flows ◽  
Ensemble Averaging ◽  
Particle Sedimentation ◽  
Turbulence Effects

AbstractWe report on laboratory experiments on the motion of powder-snow avalanches along a bent chute. The avalanches are simulated as turbulent boundary-layer flows of polystyrene particles in still water along a chute consisting of a straight inclined part, a curved part and a second, possibly inclined, run-out zone. An ultrasonic measuring technique is used to determine mean particle speeds (via the Doppler shift of the reflected signal) and the particle concentration (via the attenuation of the echoes). By ensemble averaging, individual turbulence effects are eliminated. As measuring procedures, profiles were determined for particle velocity and density across the boundary layer; these were taken (i) for the avalanche tail along the entire track, i.e. in the steep part and the run-out zone, and (ii) for the avalanche head in the run-out zone below the kink in the terrain. Moreover, time sections of velocity and density (i.e. time series at fixed positions along a line through the boundary layer) were recorded and the particle mass deposited in the various zones of the track was measured.The analysis of the data reveals the following results: a concave change in the terrain topography acts as a very efficient mechanism for particle sedimentation, thus affecting particle concentration and velocity, and considerable reduction close to the ground, whereas the density is reduced throughout the depth, thus leading to a considerable reduction of dynamic pressure close to the ground and leaving it somewhat greater at higher altitudes. We conclude with practical considerations for the field glaciologist.

A Theory for Fine Particle Deposition in 2-D Boundary Layer Flows and Application to Gas Turbines

1981 ◽  
Author(s):  
M. Agengiiturk ◽  
E. F. Sverdrup
Keyword(s):  
Boundary Layer ◽  
Gas Turbines ◽  
Particle Deposition ◽  
Magnitude Estimate ◽  
Boundary Layer Flows ◽  
Order Of Magnitude ◽  
Layer Flow ◽  
The Mathematical Model ◽  
Detailed Application ◽  
Flow Particle

A theory is presented to predict deposition rates offineparticles in two-dimensional compressible boundary layer flows. The mathematical model developed accounts for diffusion due to both molecular and turbulent fluctuations in the boundary layer flow. Particle inertia is taken into account in establishing the condition on particle flux near the surface. Gravitational settling and therm are not considered. The model assumes that the fraction of particles sticking upon arrival at the surface is known, and thus, treats it as a given parameter. The theory is compared with a number of pipe and cascade experiments, and a reasonable agreement is obtained. A detailed application of the model to a turbine is also presented. Various regimes of particle transport are identified, and the range of validity of the model is discussed. An order of magnitude estimate is obtained for the time the turbine stage can be operated without requiring cleaning.

Sign in / Sign up

Export Citation Format

Share Document