Browsing by Subject "Surface roughness"
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Item Adhesion of particles on indoor flooring materials(2007-12) Lohaus, James Harold, 1968-; Siegel, Jeffrey A.This dissertation involved a theoretical and experimental investigation of the adhesive forces between spherical particles of four different diameters and two selected flooring materials under different air velocities. Previous theoretical work and experiments described in the literature tended to be conducted with idealized surfaces, and therefore have limited applicability to indoor environments. Controlled experiments were designed, constructed and executed to measure the air velocity required to overcome adhesion forces. The diameters of the particles investigated were 0.5, 3.0, 5.0 and 9.9 [mu]m, and the flooring materials were linoleum and wooden flooring. The critical velocity, the flow at which 50% of the particles detached, is presented as a function of particle diameter for each surface. The measured values were then compared to empirical and theoretical models as well as to a scaling analysis that considers component forces that act on a particle-surface system. The results suggest that critical velocity decreases with increasing particle diameter and that existing models have limited applicability to resuspension from flooring materials.Item An Investigation of Light Scattering by Irregular Ice Crystals via PSTD(2014-07-28) Zhang, JianingWe implement the Pseudo-Spectral Time Domain(PSTD) algorithm with Convolutional Perfect Matched Layer(CPML). Comparisons were conducted to test its performance with Mie's method. Results illustrate its good performance. More tests are still needed to determine the validity PSTD with CPML. We propose a random field model for surface irregularities of ice crystals with roughened surfaces. Results using this model show that reflection probability decreases exponentially as the roughness is increased linearly. We also apply a holographic Muller matrix imaging technique for roughened particle characterization within this model. Simulations indicate that even a small perturbation on the surface will result in quite different patterns using this holographic Muller matrix method. This imaging method may be useful for the cloud imaging and particle characterization. We also study the effects of volume irregularities, in the form of air bubbles, on the scattering properties of ice crystals. Results show that such volume inhomogeneity leads to phase functions smoothing and the reduction of backscattering in comparison with homogeneous cases. The distribution of air bubbles in ice crystals also has a significant influence on the phase function of inhomogeneous ice crystals.Item Analysis of surface roughness for end milling operations(Texas Tech University, 1983-05) Arias, Evelio RNot availableItem Determination of metal removal rate with surface finish restriction(Texas Tech University, 1981-08) Ray, Dilip KumarNot availableItem Development of a hybrid DSMC/CFD method for hypersonic boundary layer flow over discrete surface roughness(2012-05) Stephani, Kelly Ann; Varghese, Philip L.; Goldstein, David Benjamin, doctor of aeronautics.; Moser, Robert; Raja, Laxminarayan; Levin, DeborahThis work is focused on the development of a hybrid DSMC/CFD solver to examine hypersonic boundary layer flow over discrete surface roughness. The purpose of these investigations is to identify and quantify the non-equilibrium effects that influence the roughness-induced disturbance field and surface quantities of interest for engineering applications. To this end, a new hybrid framework is developed for high-fidelity hybrid solutions involving five-species air hypersonic boundary layer flow applications. A novel approach is developed for DSMC particle generation at a hybrid interface for gas mixtures with internal degrees of freedom. The appropriate velocity distribution function is formulated in the framework of Generalized Chapman-Enskog Theory, and includes contributions from species mass diffusion, shear stress and heat fluxes (both translational and internal) on the perturbation of the equilibrium distribution function. This formulation introduces new breakdown parameters for use in hybrid DSMC/CFD applications, and the new sampling algorithm allows for the generation of DSMC internal energies from the appropriate non-equilibrium distribution for the first time in the literature. The contribution of the internal heat fluxes to the overall perturbation is found to be of the same order as the stress tensor components, underscoring the importance of DSMC particle generation from the Generalized Chapman-Enskog distribution. A detailed comparison of the transport coefficients is made between the DSMC and CFD solvers, and a general best-fit approach is developed for the consistent treatment of diffusion, viscosity and thermal conductivity for a five-species air gas mixture. The DSMC VHS/VSS model parameters are calibrated through an iterative fitting approach using the Nelder-Mead Simplex Algorithm. The VSS model is found to provide the best fit (within 5% over the temperature range) to the transport models used in the CFD solver. The best-fit five-species air parameters are provided for general use by the DSMC community, either for hybrid applications or to provide improved consistency in general DSMC/CFD applications. This hybrid approach has been applied to examine hypersonic boundary layer flow over discrete surface roughness for a variety of roughness geometries and flow conditions. An (asymmetric) elongated hump geometry and (symmetric) diamond shaped roughness geometry are examined at high and low altitude conditions. Detailed comparisons among the hybrid solution and the CFD no-slip and slip wall solutions were made to examine the differences in surface heating, translational/vibrational non-equilibrium in the flow near the roughness, and the vortex structures in the wake through the Q-criterion. In all cases examined, the hybrid solution predicts a lower peak surface heating to the roughness compared to either CFD solution, and a higher peak surface heating in the wake due to vortex heating. The observed differences in vortex heating are a result of the predicted vortex structures which are highlighted using the Q-criterion. The disturbance field modeled by the hybrid solution organizes into a system of streamwise-oriented vortices which are slightly stronger and have a greater spanwise extent compared to the CFD solutions. As a general trend, it was observed that these differences in the predicted heating by the hybrid and CFD solutions increase with increasing Knudsen number. This trend is found for both peak heating values on the roughness and in the wake.Item Effects of surface mineralogy and roughness on CO2 wettability of the Mount Simon sandstone; implications for predicting CO2 storage capacity and pore scale transport(2016-05) Botto, Julien; Werth, Charles; Liljestrand, HowardWettability is a key reservoir characteristic influencing geological carbon sequestration (GCS) processes such as CO2 transport and storage capacity. Wettability is often determined on limited number of reservoir samples by measuring the contact angle at the CO2/brine/mineral interface, but the ability to predict this value has not been explored. In this work, minerals comprising a natural reservoir sample were identified, and the influence of their surface roughness, surface charge, and location in the sample on contact angle was quantified to evaluate controlling mechanisms and predictive models. A core sample was obtained from Mount Simon formation, a representative siliciclastic reservoir that is the site of Department of Energy CO2 injection project. Quartz, microcline, illite, hematite, illite + hematite were identified as dominant minerals in the core, and contact angle (θ) measurements were conducted over a wide range of pressure (290-3625 psi) at 40⁰C. At supercritical conditions, individual minerals and the Mount Simon sample were strongly water wet, with contact angles between 27⁰ and 45⁰ and contact angle generally increased with surface roughness, suggesting that brine is trapped in roughness pits between CO2 and the substrate. There was no relationship between contact angle and surface charge. A thin section of the Mount Simon sandstone was examined with a compound light microscope, and reddish precipitates coating quartz and feldspar grains were apparent. These were evaluated with environmental scanning electron microscopy (ESEM) and energy dispersive X-ray spectroscopy (EDS). ESEM images show precipitate morphology that is consistent with clay coatings. The EDS results identify regions of the precipitate with high iron content. Several predictive models for contact angle were evaluated, including the Wenzel, and Cassie-Baxter models, plus new modifications of these that account for alternative surface roughness geometries and/or the fraction of different minerals comprising the reservoir sample surface. Modeling results suggest the fraction of illite/hematite covering Mount Simon grain surfaces is the most important reservoir characteristics that control wettability. To our knowledge, this is the first study that provides mechanistic insights into the characteristics of individual minerals affecting the wettability of a natural reservoir sample.Item Near-field flow structures and transient growth due to subcritical surface roughness(2010-05) Doolittle, Charles Jae, 1985-; Goldstein, David Benjamin, doctor of aeronautics; Tinney, CharlesAn immersed boundary spectral method is used to simulate laminar boundary layer flow over a periodic array of cylindrical surface roughness elements. Direct comparisons are made with experiments by using a roughness-based Reynolds number Re[subscript k] of 216 and a diameter to spanwise spacing ratio d/[lamda] of 1/3. Near-field differences between three similar studies are presented and addressed. The shear layer developed over the roughness element produces the downstream velocity deficit region while splitting of the vortex sheet shed the trailing edge forms its lateral modes. Additional geometrical configurations are simulated for comparisons with experimental results and future analysis by linear stability theory. Total disturbance energy E[subscript rms] is fairly consistent with experimental results while spanwise energy components vary significantly. Physical relaxation of the disturbance wake is found to remain a prominent issue for this simulation technique.Item Process-based aerodynamic roughness model for evaporation predictions from free water surfaces(Texas Tech University, 1998-12) Darwish, MukaddesThe process of evaporation is a complex phenomenon, which includes physical processes in several areas of physics. Accurate estimation of evaporation is important for designing and planning projects in which a water balance is key factor as well as for conservation of water. Although considerable progress has been made in understanding and measuring evaporation, the methods used in the past have serious short-comings measuring evaporation and thus developing more accurate measurements and predictions is needed. One approach to the prediction of evaporation from free water surfaces is through the use of the Borrelli-Sharif combination method which requires standard meteorological data. However, accuracy of the resulting estimation is dependent upon the interaction of wind profile and the determination of aerodynamic roughness, ZQ. It is evident that evaporation rate is influenced by the mean and turbulent flow properties near the surface of a given body of water. If the aerodynamic roughness can be estimated for the water surface, then the accuracy of predicting evaporation from that free-water surface will be greatly improved. In this study a formula is proposed for determining the aerodynamic surface roughness parameter for free water surfaces. The model is process based using the energy -transfer theory describing the reaction between wind and water surface. Wind is the main force, which causes the waves on water surfaces. Surface roughness of water is directly influenced by the velocity of the wind. The equation developed in this study predicts the wave height as a function of wind speed, and then surface roughness as a function of the wave height. This model expands the overall accuracy of evaporation prediction from free water surfacesItem Surface roughness of natural rock fractures : implications for prediction of fluid flow(2010-05) Slottke, Donald Timothy; Sharp, John Malcolm, Jr., 1944-; Ketcham, Richard A; Cardenas, M. Bayani; Laubach, Stephen E; Mace, Robert EWhere open, connected fractures are present, they dominate both fluid flow and transport of solutes, but the prediction of hydraulic and transport properties a priori has proven exceedingly difficult. A major challenge in predicting solute transport in fractured media is describing the physical characteristics of a representative surface that is appropriate to modeling. Fracture aperture, roughness, and channeling characteristics are important to predict flow and transport in hard rock terrains. In areas with little soil cover, fracture mapping can indicate areas or directions of greater permeability but not the magnitudes. Both cover and complex geology can limit mapping. Hand samples are generally available and upscaling from their properties would be highly beneficial. Assessing the impact of roughness on field-scale fluid flow through fractured media from samples of natural fractures on the order of 100cm² assumes a relationship between fracture morphology and discharge is either scale invariant or smoothly transformable. It has been suggested that the length scale that surface roughness significantly contributes to the discharge falls within the size of a typical hand sample, but few data exist to support extension of small-scale relationships to larger scales. I analyze the results of flow tests on a single fracture through a 60 x 30cm block of rhyolitic tuff. The results are compared with relationships of smaller samples in a similar tuffs and granites. The data are processed to yield regularly gridded surface elevations. Describing roughness as a ratio of surface area to footprint, variances of the roughnesses of surface covering equivalently sized square samples are plotted against sample size to determine if a representative surface exists. For specimens of fractures measuring up to 25 x 29cm, a 3.2 x 3.2cm sample of granite with an iron oxide/clay fracture skin yields a reasonable expression of the roughness of the entire surface. The number of data points included in a sample of this size transcends skin type, composition and grain/crystal size. The results suggest that the unmodified cubic law is valid for the range of gradients expected in the field using the geometric mean of areal aperture data to estimate hydraulic aperture. The data also indicate that fracture aperture is not well predicted by single aperture measurements or even by averaging along a particular scan line; three-dimensional laboratory analysis and/or field testing are required. There may be a suitable scale of data for upscaling fracture roughness on the order of 10cm². However, due to mismatch between top and bottom surfaces inherent in natural fractures, aperture samples are not consistent across the specimen and cannot be scaled. Upscaling of other factors, such as flow channeling, remain to be tested.Item The cumulative effects of roughness and Reynolds number on NACA 0015 airfoil section characteristics(Texas Tech University, 1984-05) Lewis, Kevin WayneIn this study, wind tunnel tests were made on a NACA 0015 airfoil section to examine the combination of scale and surface roughness effects. Reynolds numbers of 110,000 and 220,000 were used to determine scale effects. Roughness effects were obtained by applying roughness elements with heights of 0.111, 0.282, and 0.564 percent of the airfoil chord length. it was found that each combination of Reynolds number and roughness results in a unique set of lift and drag coefficients for a given angle of attack.Item The Effect of Blade Roughness on Wind Turbine Performance(Texas Tech University, 1982-12) Thompson, Douglas EIn this study, the effect of various degrees of blade roughness on the performance of horizontal axis wind turbines is investigated analytically. The roughness effects are analyzed in terms of the annual energy output and cost effectiveness. A computer model has been developed to quantify the effects of roughness. The model incorporates a correlation of experimental airfoil data for any degree of roughness and Reynold's number. Additionally, procedures for reducing surface roughness effects based on blade pitch variations have been evaluated. Three turbines, with rated power outputs of 25, 400, and 2000 kW, are cited as case studies to illustrate surface effects.Item The effects of surface roughness on convection with external flow(Texas Tech University, 1982-12) Luttrell, Jeffrey PaulThe receiver external heat transfer geometry for a fixed-mirror, distributed-focus solar power station was simulated with a 3-inch diameter, 12-inch long coil of 0.375-inch diameter stainless steel tubing. The coil was heated electrically and the heat transfer equated to electrical power. Free convection tests were made with the coil axis varied in steps from horizontal to vertical. Forced convection tests were made at four orientations of the coil axis relative to the flow direction: perpendicular, 60, 45 and 30 degrees. Reynolds numbers ranged from 3,000 to 80,000 for the forced convection tests. Temperature differences ranged from 300 to 950 F. Free convection results showed a greater increase of convection with increasing-temperature difference than a smooth cylinder. Forced convection results were similar to those for a smooth cylinder in cross-flow correlations. Contrary to experience with smooth cylinders, convection was increased when the flow had a component along the coil axis and the Reynolds number was greater than 6000.Item Tribochemical investigation of microelectronic materials(2009-06-02) Kulkarni, Milind SudhakarTo achieve efficient planarization with reduced device dimensions in integrated circuits, a better understanding of the physics, chemistry, and the complex interplay involved in chemical mechanical planarization (CMP) is needed. The CMP process takes place at the interface of the pad and wafer in the presence of the fluid slurry medium. The hardness of Cu is significantly less than the slurry abrasive particles which are usually alumina or silica. It has been accepted that a surface layer can protect the Cu surface from scratching during CMP. Four competing mechanisms in materials removal have been reported: the chemical dissolution of Cu, the mechanical removal through slurry abrasives, the formation of thin layer of Cu oxide and the sweeping surface material by slurry flow. Despite the previous investigation of Cu removal, the electrochemical properties of Cu surface layer is yet to be understood. The motivation of this research was to understand the fundamental aspects of removal mechanisms in terms of electrochemical interactions, chemical dissolution, mechanical wear, and factors affecting planarization. Since one of the major requirements in CMP is to have a high surface finish, i.e., low surface roughness, optimization of the surface finish in reference to various parameters was emphasized. Three approaches were used in this research: in situ measurement of material removal, exploration of the electropotential activation and passivation at the copper surface and modeling of the synergistic electrochemical-mechanical interactions on the copper surface. In this research, copper polishing experiments were conducted using a table top tribometer. A potentiostat was coupled with this tribometer. This combination enabled the evaluation of important variables such as applied pressure, polishing speed, slurry chemistry, pH, materials, and applied DC potential. Experiments were designed to understand the combined and individual effect of electrochemical interactions as well as mechanical impact during polishing. Extensive surface characterization was performed with AFM, SEM, TEM and XPS. An innovative method for direct material removal measurement on the nanometer scale was developed and used. Experimental observations were compared with the theoretically calculated material removal rate values. The synergistic effect of all of the components of the process, which result in a better quality surface finish was quantitatively evaluated for the first time. Impressed potential during CMP proved to be a controlling parameter in the material removal mechanism. Using the experimental results, a model was developed, which provided a practical insight into the CMP process. The research is expected to help with electrochemical material removal in copper planarization with low-k dielectrics.Item Wind tunnel blockage corrections: a computational study(Texas Tech University, 2004-08) Sahini, DeepakWind tunnel blockage testing has been a wide spread traditional practice in the automobile industry for many years; but the tests conducted have been associated with the so called blockage effects, which arise due to the constrained flow nature inside the wind tunnel test section and over the blockages. These blockage effects need to be corrected in order to comprehend the test results similar to those of the actual road conditions. CFD has emerged as a tool to determine the blockage effects and provide corrections using computational techniques. In this present study, two such CFD packages, namely PHOENICS and AIRFL03D, are used for determining the wind tunnel blockage effects. The problems taken into consideration are both two dimensional and three dimensional flow cases. The test section domain height is varied so as to produce different blockage ratios, keeping the blockage dimensions constant. A two dimensional free stream case with blockage l/h ratio variation is tested and compared with experimental results. In the other cases, the two packages are compared with each other for pressure and velocity distributions and drag coefficients. A grid independent study was performed for one case. Finally, blockage correction equations are obtained for all the test cases.