Browsing by Subject "Fluids"
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Item A New Facility for Studying Shock Wave Passage over Dust Layers(2013-05-30) Marks, BrandonTo ensure safety regarding dust explosion hazards, it is important to study the dust lifting process experimentally and identify important parameters that will be valuable for development and validation of numerical predictions of this phenomenon. A new shock tube test section was developed and integrated into an existing shock tube facility. The test section allows for shadowgraph or laser scattering techniques to track dust layer particle motion. The test section is designed to handle an initial pressure of 1 atm with an incident shock wave velocity up to Mach 2 to mimic real world conditions. The test section features an easily removable dust pan and inserts to allow for adjustment of dust layer thickness. The design allows for the changing of experimental variables including initial pressure, Mach number, dust layer thickness and characteristics of the dust itself. A separate vacuum manifold was designed to protect existing equipment from negative side effects of the dust. A study was performed to demonstrate the capabilities of the new facility and to compare results with experimental trends formerly established in the literature. Forty-micron limestone dust with a layer thickness of 3.2 mm was subjected to Mach 1.22 and 1.38 shock waves, and a high-speed shadowgraph was used for flow visualization. Dust layer rise height was graphed with respect to shock wave propagation. Dust particles subjected to a Mach 1.38 shock wave rose more rapidly and to a greater height with respect to shock wave propagation than particles subjected to a Mach 1.22 shock wave. These results are in agreement with trends found in the literature, and a new area of investigation was identified.Item Constant force and constant velocity experiments in concentrated suspensions(Texas Tech University, 2003-08) Reardon, Patrick THomogeneous materials are characterized by intrinsic properties such as density, thermal conductivity, and viscosity that are independent of sample size and of the state of stress of the material. For example, experiments with a test sphere traversing in a homogeneous Newtonian fluid would determine the same viscosity by measuring the force on the test sphere traveling at a constant velocity or by measuring the velocity of the test sphere under a constant force. Recent theoretical calculations have shown that a test sphere settling in suspensions of neutrally buoyant spheres will experience a larger resistance to motion traveling at a constant velocity through a region in the cylinder free of end effects than moving under a constant force when the spheres are of similar size or the test sphere is much smaller than the suspending spheres. Hence, constant force and constant velocity experiments would measure different apparent viscosities even in a suspension at infinite dilution. The objective of this paper is to examine this surprising prediction using concentrated suspensions of neutrally buoyant particles in viscous Newtonian liquids under conditions such that only hydrodynamic forces exert an appreciable effect. Experiments have been performed to explore the difference between the apparent viscosity of a suspension as determined by a constant gravitational force applied to a test sphere (falling-ball rheometry) and the apparent viscosity of the same suspension measured with a non-rotating test sphere towed (pulling-ball rheometry) with uniform velocity through the suspension and extrapolated to zero string length. The relative viscosity is the apparent viscosity of the suspension relative to that of the pure suspending fluid, çr, The model suspensions used in these experiments were made from large, monomodal, neutrally buoyant particles in viscous Newtonian fluids. These experiments were conducted using cylinders of sufficient length that end effects were unimportant in the center section of the column. When tested against Newtonian test fluids both pulling ball and falling ball experiments produce accurate measurements of the relative viscosities. For the same size balls and suspensions, çr measured in the pulling-ball experiments was larger than those measured in the falling-ball experiments. The ratio of the two viscosities increases linearly as the volume fraction of solids in the suspension, ö, increases from 0.1 to 0.5. The ratio of the two relative viscosities is not a strong function of the ratio of the size of the suspended balls to the test sphere.Item Continuum limits in concentrated suspensions(Texas Tech University, 2003-08) Chawla, VibhaThe viscosity of a Newtonian fluid is independent of the sample size used to determine this property. Literature reports (Mondy et al. (1988)) and preliminary experimental results from our working group using falling-ball rheometry suggested that in suspensions the viscosity was a fiinction of the number of suspended particle diameters across the containing cylinder or conduit. The model suspensions were made from large, monomodal, neutrally buoyant particles in viscous Newtonian fluids. These results indicated that the viscosity of the suspension relative to that of the pure suspending fluid, r|r, went through a minimum when the rafio of the radius of the containing cylinder, Rcyi, to the radius of the suspended particles, as, was 12 then increased monotonically as Rcyi/as increased to approximately 127. The objective of this investigation was to test these claims and to uncover the underlying physics that govern this phenomenon. The use of falling balls to measure the viscosity of Newtonian fluids is well developed. Velocity data obtained in the middle section of the containing cylinder at least one diameter from the top and bottom surfaces leads to accurate measurements of the viscosity. These same assumptions were being used in falling-ball measurements in suspensions. In the initial portion of this investigation, we found that these assumptions were valid for dilute and moderately concentrated suspensions (solids fraction, ^<0.2). However in more concentrated suspensions ((t)=0.5), our experiments showed that these assumptions are in error for suspensions of particles with small Rcyi/as and that end effects in these systems can extend over an order of magnitude fiirther than in pure Newtonian fluids. As Rcyi/as increases, the end effects decrease until they are indistinguishable from those observed in Newtonian fluids. Subsequent experiments were conducted using cylinders of sufficient length that end effects could be neglected in the center section of the column. These same suspensions with a narrow particle size distribution showed no dependence on Rcyi/as. Hence, the original reports of the r|r dependence on Rcyi/as resulted from studies conducted in cylinders of insufficient length for the falling balls to achieve a steady-state velocity. Further experiments for suspensions with very large Rcyi/as and very broad particle distributions show much larger viscosities and shear thinning behavior. It was found that the onset of this non-Newtonian behavior was very sensitive to the breadth of the particle size distribution.Item Local feedback regularization of three-dimensional Navier-Stokes equations on bounded domains(Texas Tech University, 1997-05) Balogh, AndrasThe specific problem we consider here is inspired by recent advances in the control of nonlinear distributed parameter systems and its possible applications to hydrodynamics. The main objective is to investigate the extent to which the 3-dimensional Navier-Stokes system can be regularized using a particular, physically motivated, feedback control law. The specific choice of feedback mechanism is motivated by a work of O.A. Ladyzhenskaya [7] in which she introduces a modification of the Navier-Stokes equation on a three dimensional bounded domain and shows that the resulting perturbed system possesses global dynamics and, furthermore, this dynamics is stable. It is in this sense that we understand the system to be regularized.Item On the linear stability problem for Jeffery-Hamel flows(2015-05) Carlson, William Zechariah; Vishik, Mikhail; Chen, Thomas; Pavlovic, Natasa; Vasseur, Alexis; Bogard, DavidWe study the linear stability of a family of Jeffery-Hamel solutions which satisfy a zero flux condition. With a suitable regularization of these velocity profiles we show that the linearized perturbation equation is well-posed on a weighted L² space with a certain class of radial weights, in the example of a half plane or in the whole plane. We prove that the perturbed Stokes operator of this system is the generator of a strongly continuous analytic semigroup. We also describe some formal asymptotics under which the linear stability problem could be reduced to a one dimensional problem for which we state a formal perturbation theory.