Browsing by Subject "Surface roughness"

Now showing 1 - 8 of 8

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.
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, Deborah
This 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.
Effect of laser polishing on fatigue behavior of additively manufactured IN718
(2022) Lee, Seungjong; Bureš, Martin; Shao, Shuai; Wells, Douglas N.; Zetek, Miroslav; Kepka, Miloslav; Shamsaei, Nima
This study investigates the effect of laser-polishing on the fatigue behavior of Inconel 718 fabricated using laser powder bed fusion process. Three different conditions including as-built and laser-polished using two different process parameters are considered. Uniaxial tension- compression fatigue tests are conducted in strain-controlled mode to examine the fatigue behavior for each condition. In addition, surface roughness measurements and fractography using optical microscopy and porosity measurements using the X-ray computed tomography are also performed for all conditions. The results indicate that laser-polishing alone does not improve fatigue performance, even though it can significantly reduce surface roughness. The beneficial effects of the smoother surfaces may have been countered by the volumetric defects close to the surface induced by laser-polishing. The fracture surfaces also reveal that fatigue cracks are initiated from the defects close to the surface, and therefore, fatigue behavior is not improved.
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, Howard
Wettability 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.
Investigating surface topography effects on directional emissivity of metallic additively manufactured parts
(2019-09-20) Taylor, Samantha Sparr; Beaman, Joseph J.; Seepersad, Carolyn C; Taleff, Eric M; Heltzel, Alexander J; Forrest, Eric C
Researchers are focusing on qualification methods and simulations to gain a better understanding of metal powder bed additive manufacturing (AM) processes. Because of the direct relationship between thermal history and mechanical behavior, in-situ thermal monitoring is key in gauging the quality of both the process and produced parts. To accurately monitor the temperatures of an AM process, key environment and object parameters need to be known, most importantly, object emissivity. The emissivity of an object is dependent on several variables, including: wavelength of light, material composition, temperature, and surface topography. Most have been concerned with the thermal emissivity dependence on temperature since large temperature ranges are seen in metal powder bed processes, but there is also an extensive range of surfaces produced by AM. This work will focus on discovering what surface characteristics control directional thermal emissivity. In addition to defining the surface characteristics, in build conditions will be simulated while conducting thermal measurements of AM parts to quantify errors that result from incorrect emissivity assumptions. Lastly, a method for determining the surface topography in-situ to allow for layerwise correction of emissivity will be implemented in an additive machine
Investigation of surface roughness of natural rock fractures using high-resolution X-ray computed tomography and laboratory flow test measurements
(2005-12) Thompson, Clark; Sharp, John Malcolm, Jr., 1944-
Fluid flow through natural rock fractures is an important - and often dominant - factor in many aquifer and reservoir systems. Rock fractures are rough-walled, and this surface roughness introduces complexities. The analytically-derivable 'cubic law' describes laminar flow behavior through smooth, parallel plates. Adjustment to the cubic law for surface roughness has been sought since the 1950s but remains elusive. This study evaluates the feasibility of using X-ray computed tomography (CT) to measure surface roughness of natural rock fractures. Classical roughness parameters are summarized. CT and its application to imaging fracture apertures are reviewed. The CT imaging of two natural fractures is described. The resulting 3-D surface data are analyzed using conventional statistics. Power spectral density analysis using the power law method of Brown (1995) is described and performed. The issue of spatial stationarity of the surfaces is examined. The relevant concepts from fluid mechanics are summarized. The pioneering work of Lomize (1951) and Louis (1969) is reviewed. A flow test apparatus is designed and used to test a natural rock fracture. The results of 301 flow tests are summarized and analyzed. These results are compared to the roughness correction factors of Lomize (1951) and Louis (1969).
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, Charles
An 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.
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 E
Where 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.