272 research outputs found
Point source dispersion in a direct numerical simulation of turbulent channel flow
No full textThe dispersion of a scalar quantity from point sources located in a Direct Numerical Simulation of turbulent channel flow is studied. An algorithm for tracking fluid particles or molecular (or thermal) markers is developed and tested. Accurate estimates of a number of Lagrangian characteristics of the flow, necessary for the description of the diffusion process, are reported for the case of a point source in the center of the channel. The consequences of molecular diffusivity on the effectiveness of the turbulence to disperse a foreign substance (or heat) are also explored. A new method is proposed for calculating the effect of Peclet number on the Lagrangian property autocorrelation in isotropic turbulence. Computed property autocorrelations, from a simulated experiment of point source diffusion in the center of the channel, are also reported. Finally, results for the diffusion from point sources located at the channel walls are presented and discussed.Made available in DSpace on 2011-05-07T11:54:29Z (GMT). No. of bitstreams: 2
license.txt: 4922 bytes, checksum: 910b249b4beec47e7ab768910c8f966f (MD5)
9210875.pdf: 7723563 bytes, checksum: 5ab88d8b2e26a0a4b9af3bb7a3600749 (MD5)
Previous issue date: 1991Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Howard Ding ([email protected]) on 2011-05-07T14:34:06Z
Item is restricted indefinitely.Restriction data tranferred 2014-07-01T11:12:52-05:00
Original Data
Group with Access UIUC Users [automated]
Release Date: none
Reason: ETDs are only available to UIUC Users without author permissionETDs are only available to UIUC Users without author permissionU of I Onl
An experimental study of solid particle motion in a turbulent liquid pipe flow
No full textAn experimental study of the motion of 100 micron diameter glass and stainless steel spheres in a fully developed turbulent liquid pipe flow was conducted. Furthermore, the liquid, water, was directed vertically downward through a 5.08 cm inside diameter plexiglas tube. One goal was to measure the turbulence properties of the particles in the r- plane with a previously developed axial viewing photographic technique. Another goal was to determine the effects of the inherent inhomogeneities of turbulent pipe flow on the results.Several particle turbulence properties were measured. Radial direction Lagrangian and Eulerian particle diffusion coefficients were obtained at Reynolds numbers (based on bulk velocity and pipe diameter) ranging from 15,700 to 141,000. Radial and azimuthal direction particle turbulence intensity profiles for both particles were obtained at Re = 16,000 and 72,000. The technique also permitted the radial and azimuthal direction particle acceleration to be measured.A new phenomenon was discovered which is the result of the inhomogeneities of turbulent pipe flow. It was found that under certain conditions, the particles that diffuse to the pipe wall may get temporarily or permanently trapped there. They get trapped in a patterned manner as well. Inhomogeneities were also found to affect the measured radial direction particle concentration and average velocity profiles, but only under certain conditions.Made available in DSpace on 2011-05-07T12:38:15Z (GMT). No. of bitstreams: 2
license.txt: 4922 bytes, checksum: 910b249b4beec47e7ab768910c8f966f (MD5)
8916324.pdf: 10576671 bytes, checksum: b210936672177b23cd16c305a6ee4fb8 (MD5)
Previous issue date: 1989Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Howard Ding ([email protected]) on 2011-05-07T14:43:40Z
Item is restricted indefinitely.Restriction data tranferred 2014-07-01T11:19:08-05:00
Original Data
Group with Access UIUC Users [automated]
Release Date: none
Reason: ETDs are only available to UIUC Users without author permissionETDs are only available to UIUC Users without author permissionU of I Onl
Mass transfer in turbulent pulsating flows
No full textItem marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Howard Ding ([email protected]) on 2011-05-07T14:58:36Z
Item is restricted indefinitely.Restriction data tranferred 2014-07-01T11:27:34-05:00
Original Data
Group with Access UIUC Users [automated]
Release Date: none
Reason: ETDs are only available to UIUC Users without author permissionETDs are only available to UIUC Users without author permissionU of I OnlyThis thesis reports on the effects of imposed flow oscillations on the mass transfer coefficient and the mass transfer intensity in a turbulent flow.The equations for the turbulent fluctuations in the velocity and concentration fields and the equations for the mean and oscillating components of the phase averaged concentration field are derived and presented. From examining these equations, one can determine which terms would cause changes in the time averaged velocity and concentration fields and which terms would cause oscillations in the phase averaged velocity and concentration fields.Experiments were performed in a two inch diameter horizontal pipe. A reciprocating piston pump imposed the pulsations in the mean flow rate. Mass transfer coefficients were measured electrochemically. A platinum plated brass section served as a cathode to measure the average mass transfer coefficient and to insure a fully developed concentration boundary layer. Platinum electrodes, insulated from the cathode, were embedded in the cathode to measure the phase averaged mass transfer coefficient and the fluctuations in the phase averaged mass transfer coefficient. Numerical methods were developed to solve the phase averaged mass balance equation by modeling the phase averaged Reynolds transport with an eddy diffusivity model.The following results were obtained in this study: The imposed flow oscillations have no effect upon the time averaged mass transfer coefficient or the time averaged mass transfer intensity. The imposed oscillations in the velocity field cause oscillations in the phase averaged mass transfer coefficient and the phase averaged mass transfer intensity. The oscillations in the streamwise velocity fluctuations cause oscillations in the normal velocity fluctuations which cause oscillations in the phase averaged mass transfer coefficient and the phase averaged mass transfer intensity. The pseudo steady state and relaxation eddy diffusivity models provide good agreement with the experimental data at low frequencies of pulsation. However, at high frequencies of pulsation, there is an interaction between the imposed pulsations and the turbulence that is not included in these models. A modified eddy diffusivity model in which the eddy diffusivity is a function of \omega\sp{+2} provided good agreement with the experimental results at all frequencies that were studied.Made available in DSpace on 2011-05-07T13:44:31Z (GMT). No. of bitstreams: 2
license.txt: 4922 bytes, checksum: 910b249b4beec47e7ab768910c8f966f (MD5)
9010989.pdf: 4467409 bytes, checksum: 4f9745e912c4f1b862e34bf0ef773aac (MD5)
Previous issue date: 198
The study of gas absorption at a wavy air-water interface
No full textETDs are only available to UIUC Users without author permissionU of I OnlyTwo techniques were developed to relate gas absorption to waves formed at the interface of an air-water flow. The first measured the instantaneous concentration profile of oxygen in water very close to the interface. The second measured the instantaneous wave slope.The concentration measurement is new; it is the first to determine the concentration gradient within the mass transfer boundary layer of this system. The technique uses a tracer whose fluorescent intensity is inversely proportional to oxygen concentration. The fluorescence of the tracer was recorded using a CCD camera so that spatial resolution is preserved.Measurements were obtained in a horizontal channel with air and water flowing concurrently. Concentration profiles were measured at a smooth interface, gas velocity = 1.5 m/s, and at a wavy interface, gas velocity = 2 m/s. The mass transfer boundary layer at the smooth interface had a thickness of 700 microns which is a dimensionless thickness of y\sp+ = 6. It was found that at a smooth interface the gas absorption rate is constant with time.Measurements with waves showed a much larger mass transfer rate which varied with time. The mass transfer boundary layer varied from less than 100 microns (y\sp+ = 0.9) to 600 microns (y\sp+ = 5.4). The lower limit that could be detected was 100 microns. There was some evidence that the very large mass transfer rates (boundary layers less than 100 microns) are associated with large wave slopes.Wave slopes were obtained by measuring the optical displacement of a laser beam which vertically pierces the water surface and bends due to the curvature at the surface. Measurements were obtained at various gas and liquid Reynolds numbers.The data suggest that wave slope rather than wave height is the appropriate parameter to relate mass transfer to wavy motion. A consequence of this is that mass transfer is related to higher frequency velocity fluctuations than would be suggested from wave height spectra.Made available in DSpace on 2011-05-07T12:59:55Z (GMT). No. of bitstreams: 2
license.txt: 4922 bytes, checksum: 910b249b4beec47e7ab768910c8f966f (MD5)
9211038.pdf: 3848073 bytes, checksum: d67e45d7935bc4ccd2ca728926bc49e1 (MD5)
Previous issue date: 1991Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Howard Ding ([email protected]) on 2011-05-07T14:48:50Z
Item is restricted indefinitely.Restriction data tranferred 2014-07-01T11:22:09-05:00
Original Data
Group with Access UIUC Users [automated]
Release Date: none
Reason: ETDs are only available to UIUC Users without author permissio
Transport processes in a direct numerical simulation of turbulent channel flow
No full textA direct numerical simulation of fully-developed, time-dependent, three-dimensional turbulent flow in a channel is used to investigate turbulent transport processes. Detailed properties of the turbulent velocity field are presented. Three different transport processes are explored using this extensive data base. The first is the identification of the origin and fate of flow-oriented structures responsible for transporting momentum close to the wall. An important finding is that they regenerate themselves by a process that appears to be weakly dependent on the outer flow. This involves the enhancement of streamwise vorticity at the wall, of opposite sign, at a location where a stress-producing eddy lifts from the wall. Another area of exploration is the analysis of how small, dense particles move in a carrier fluid and deposit on a boundary. A Stokes drag force is used in the equation of motion for the aerosol and the particles are assumed to have no influence on the flow field. It is shown that these particles accumulate in the near wall region by turbophoresis and by free-flight. They deposit due to their own inertia. A new method for identifying free-flight particles is presented and a prediction of free-flight deposition is made using fluid velocity distributions. The third subject involves the effect of Prandtl number on the transport of heat in turbulent flow between a hot wall and a cold wall. The effects of Prandtl number on the turbulent diffusivity of heat and on the dissipation of temperature fluctuations are presented. A prediction of the Nusselt number based upon the Reynolds analogy, which relates the turbulent temperature field to the turbulent velocity field, is also presented.Made available in DSpace on 2011-05-07T14:15:25Z (GMT). No. of bitstreams: 2
license.txt: 4922 bytes, checksum: 910b249b4beec47e7ab768910c8f966f (MD5)
9416340.pdf: 6866378 bytes, checksum: bdb0049e9b8f76635cebb0547115268b (MD5)
Previous issue date: 1994Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Howard Ding ([email protected]) on 2011-05-07T15:04:42Z
Item is restricted indefinitely.Restriction data tranferred 2014-07-01T11:30:56-05:00
Original Data
Group with Access UIUC Users [automated]
Release Date: none
Reason: ETDs are only available to UIUC Users without author permissionETDs are only available to UIUC Users without author permissionU of I Onl
Effect of pipe diameter on horizontal annular two-phase flow
No full textRestriction data tranferred 2014-07-01T11:32:13-05:00
Original Data
Group with Access UIUC Users [automated]
Release Date: none
Reason: ETDs are only available to UIUC Users without author permissionETDs are only available to UIUC Users without author permissionThe effect of pipe diameter on horizontal annular flow is examined. Measurements of the local film height, the local droplet flux, the local velocity, and the entrained fraction for annular flow in a 9.53 cm horizontal pipe have been obtained. The measurements are compared with the results from previous investigators for horizontal annular flow in pipes with diameters of 2.54 cm and 5.08 cm.A new large scale two-phase flow facility has been designed and constructed. The facility has the ability to incline a 26.5 m pipe at angles between positive and minus 2.5 degrees from the horizontal.Local film height measurements show that the film distribution becomes increasingly asymmetric with increasing pipe diameter. The effect of pipe diameter on the asymmetries of the liquid film distribution is predicted approximately by a Froude number. At Froude numbers below 50, the liquid is stratified as a pool at the pipe bottom.A turbulent diffusion model developed by a co-researcher for the droplet concentration distribution is in good agreement with measurements at low gas velocities and low droplet concentrations. At higher droplet concentrations, velocity measurements suggest the existence of a secondary flow in the gas which inhibits droplet settling.Entrainment correlations developed from experiments in small diameter pipes, over predict the entrained fraction in large diameter pipes. A generalized entrainment correlation based on an equilibrium rate balance between the rate of atomization of droplets from the liquid film and the rate of deposition of droplets back to the liquid film is developed. The correlation is easily interpreted for two extremes of the liquid film distribution. When the film is distributed uniformly around the pipe wall, the entrainment relation reduces to a form developed by previous researchers. For conditions where the liquid film is stratified as a pool at the pipe bottom, a new entrainment relation is developed which is in good agreement with the results.Made available in DSpace on 2011-05-07T14:28:05Z (GMT). No. of bitstreams: 2
license.txt: 4922 bytes, checksum: 910b249b4beec47e7ab768910c8f966f (MD5)
9026352.pdf: 7290986 bytes, checksum: 1c1a69925f1b169064b0cd5336fadd42 (MD5)
Previous issue date: 1990Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Howard Ding ([email protected]) on 2011-05-07T15:07:01Z
Item is restricted indefinitely.U of I Onl
A direct numerical simulation of fully developed turbulent channel flow with passive heat transfer
No full textA direct numerical simulation of a fully developed turbulent channel flow with passive heat transfer is performed. The time-dependent three-dimensional Navier-Stokes equations and advection-diffusion equation are solved numerically using a pseudospectral technique with 1,064,960 grid points in physical space (128 x 65 x 128 in x, y, z). No subgrid scale model is employed since all essential turbulence scales are resolved. The Reynolds number is 2262, based on the half channel height and bulk velocity, and the Prandtl number is 1. The Nusselt number is predicted to be 25.36. A large number of one-point turbulence statistics are computed and compared with existing experimental data taken at similar Reynolds and Nusselt numbers. Agreement with the existing experimental data is excellent except for some discrepancies in the near wall region, y\sp+ 10. A number of two-point statistical correlations with spanwise, streamwise, and/or normal separation are also computed and reported. Mean and turbulent kinetic energy, Reynolds stress, and mean and turbulent temperature variance budgets are presented. Instantaneous and conditionally averaged flow structures are also presented. The momentum and heat transport in the viscous wall region, 0 y\sp+ 30-40, is found to be controlled by wall eddies with a spanwise scale of 50\sp+ tilted 30-50 degrees from the wall and rotating in the y-z plane. These eddies are periodic in the spanwise direction with an average periodicity length of 100\sp+. The wall eddies are elongated in the streamwise direction with streamwise extent 200-400\sp+.Made available in DSpace on 2011-05-07T13:33:22Z (GMT). No. of bitstreams: 2
license.txt: 4922 bytes, checksum: 910b249b4beec47e7ab768910c8f966f (MD5)
8924888.pdf: 9344798 bytes, checksum: 0f53353b9683acfe420b05d80d22d2a5 (MD5)
Previous issue date: 1989Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Howard Ding ([email protected]) on 2011-05-07T14:56:14Z
Item is restricted indefinitely.Restriction data tranferred 2014-07-01T11:26:16-05:00
Original Data
Group with Access UIUC Users [automated]
Release Date: none
Reason: ETDs are only available to UIUC Users without author permissionETDs are only available to UIUC Users without author permissionU of I Onl
Turbulent flow through a rectangular channel
No full textStreamwise and normal turbulent velocity measurements were taken at 80 normal locations across a two-inch high rectangular water channel. A two polarization, three beam He-Ne Laser-Doppler Velocimetry system was used. The water channel was specifically designed and constructed to facilitate these optical measurements. It had negligible vibration and flow oscillation. Its length was 200 channel heights, sufficient to produce fully developed turbulent flow. The optical system had a specially designed optical table and traverse; optical glass windows were used as viewing ports.Measurements were made of the first four moments of the velocity fluctuation and the first three moments of Reynolds stress. The turbulence production and the correlation coefficient were calculated. Velocity spectra were measured for both the normal and streamwise velocity fluctuations at four to nine normal locations. Measurements were taken as close as y\sp+ = 0.6 viscous units away from the wall. The experiments were conducted at Reynolds numbers of 2457, 2777, and 18,339. The experimental results were compared to the computer simulation channel flow by Kim, Moin, and Moser. Very good agreement was found.Measurements were also made of the differential surface pressure over two sinusoidal waves. Wave amplitudes of 0.0123 and 0.03125 inches were used. Both waves had two inch wavelengths. Viscous fluid was used to extend the range of the measurements over a much larger range of Reynolds numbers than had been previously reported. Non-linearities were found at low Reynolds numbers in the differential pressure distribution over the 0.03125 inch amplitude wave, indicating a quasi-separated or separated flow. The differential pressure distribution over the 0.0123 inch amplitude wave demonstrated a linear, sinusoidal response. The experimental data were compared to computer models developed in this laboratory and were found to demonstrate only fair agreement. This is not unexpected, since the computer models predict a linear response over all experimental Reynolds numbers examined.Made available in DSpace on 2011-05-07T13:14:43Z (GMT). No. of bitstreams: 2
license.txt: 4922 bytes, checksum: 910b249b4beec47e7ab768910c8f966f (MD5)
8924913.pdf: 13922524 bytes, checksum: c9fd61fa173274736012e63e753d223a (MD5)
Previous issue date: 1989Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Howard Ding ([email protected]) on 2011-05-07T14:52:13Z
Item is restricted indefinitely.Restriction data tranferred 2014-07-01T11:24:01-05:00
Original Data
Group with Access UIUC Users [automated]
Release Date: none
Reason: ETDs are only available to UIUC Users without author permissionETDs are only available to UIUC Users without author permissionU of I Onl
The effect of drop concentration on deposition in vertical annular two-phase flow
No full textDeposition in annular two phase flow has been found to deviate from a linear rate law. At high liquid flows the rate constant is found to vary inversely with drop concentration (i.e. the rate of deposition is independent of concentration). This deviation causes concern when predicting dryout in two phase applications. To better understand this process, information on its drop size and on the behavior of drops in the turbulent gas flow are needed. Experiments were conducted in a 4.2 cm vertical pipe at an upward superficial gas velocity of 36 m/s and at liquid mass flow rates from 30 to 170 g/s. Photographic drop size measurements were obtained. Measurements of entrainment, gas velocity, slip ratio, and drop concentration were also obtained. An increase in mean drop diameters with increasing drop concentration was found.Several explanations for the non-linearity of deposition are considered. These include gas phase turbulence dampening, the decrease in turbulence velocities with increasing drop size, and particle-particle interactions.The theory of Reeks (1977) for the behavior of single particles in homogeneous isotropic turbulence and the data of Lee et al. (1989) were used to predict deposition rates based on the premise that increasing drop size decreases the turbulence of the particles. The results show that deposition is overpredicted at the higher concentrations and that a much larger increase in drop sizes, than observed, is needed for the measured rates to be predicted correctly.By assuming a small velocity difference between particles of different sizes (terminal velocities due to gravity), calculations reveal that droplet-droplet interactions are important. Drop size measurements upstream indicate that only about ten percent of these interactions need to result in coalescence in order to predict the observed change in drop distribution. A theory is proposed that suggests that interactions between larger drops halt their radial velocities so that the time for the fluid turbulence to bring them back to speed is greater than the time between interactions. The theory correctly predicts the inverse proportionality of the deposition rate constant on drop concentration at large concentrations.Made available in DSpace on 2011-05-07T12:42:35Z (GMT). No. of bitstreams: 2
license.txt: 4922 bytes, checksum: 910b249b4beec47e7ab768910c8f966f (MD5)
9512390.pdf: 4701470 bytes, checksum: a8a8f061ea4f5f90e09889ab0795f201 (MD5)
Previous issue date: 1994Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Howard Ding ([email protected]) on 2011-05-07T14:44:40Z
Item is restricted indefinitely.Restriction data tranferred 2014-07-01T11:19:41-05:00
Original Data
Group with Access UIUC Users [automated]
Release Date: none
Reason: ETDs are only available to UIUC Users without author permissionETDs are only available to UIUC Users without author permissionU of I Onl
Air-water transfer at wavy interfaces
No full textGas-water exchange is usually controlled by a thin surface layer in the liquid just beneath the interface. The structure and dynamics of the interface profoundly influence the rate of mass transfer. Of particular importance to environmental and climatical cycles is the large (3 to 5 fold) enhancement of the rate of physical absorption of lightly soluble gases that accompanies wind-generated waves. This thesis relates oxygen absorption rates in stratified flow to the interfacial structure and to the near-interface hydrodynamics of the liquid.Time-averaged mass transfer rates, two-dimensional liquid-side concentration fields, and interfacial windrow formations were measured during oxygen absorption in stratified wavy flow in a horizontal channel. The complication in making direct measurements is that the surface concentration layer is very thin (0.02 to 0.3 mm thick) and it is beneath a moving interface. A laser-induced fluorescence imaging method is described for capturing oxygen concentration variation and interfacial position for a two-dimensional field. A floating tea tracer method is described for visualizing interfacial streaks (or windrows) that form in convergence zones caused by large circulation flows.Results are presented for flows that had depths of about 5 mm and interfacial friction velocities, u\sp{\*}, of 1.01 to 1.59 cm/s. The water surfaces had flat interfaces, two-dimensional ripple waves, broadcrested waves, and chaotic pebble waves.The concentration fields show that increases in wave motions caused by increases in u\sp{\*} are accompanied by a thinning of the average layer thickness, an increase in variations of the concentration layer within an image (along the dominant wave), and a decrease in the measured concentration at the interface. Layers were observed with thicknesses that varied from 0.11 to 0.53 mm. No layers extended beyond 0.6 mm, indicating that the bulk flow was well mixed, and, therefore, turbulent. A striking feature of the concentration fields for wavy flows is what appears to be layers of higher concentration that have detached from the surface and moved into the bulk flow.Windrows were observed on the interface with spacings of 3 cm for broadcrested and 2 cm for chaotic pebble waves.Results suggest that at least two mechanisms are operative. Langmuir-type circulations, with axes in the direction of mean wind-flow, are present. They exhibit themselves in the concentration fields as variations in the mean depth of the surface concentration-layer from image to image. This behavior is interpreted as streaks which meander in and out of the image sheet. A general thinning of the layer is observed when waves are present. This thinning is characteristic of what would be expected for an increase in turbulence diffusivity. It is not possible at this point to say which of these two distinct enhancements in transport accounts for the 300 to 500% enhancement with waves.Made available in DSpace on 2011-05-07T12:35:04Z (GMT). No. of bitstreams: 2
license.txt: 4922 bytes, checksum: 910b249b4beec47e7ab768910c8f966f (MD5)
9712262.pdf: 5459288 bytes, checksum: bb8aeceb60d78b2d2fcdbeb878f52a22 (MD5)
Previous issue date: 1996Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Howard Ding ([email protected]) on 2011-05-07T14:42:55Z
Item is restricted indefinitely.Restriction data tranferred 2014-07-01T11:18:43-05:00
Original Data
Group with Access UIUC Users [automated]
Release Date: none
Reason: ETDs are only available to UIUC Users without author permissionETDs are only available to UIUC Users without author permissionU of I Onl
- …
