Richard M. Lueptow

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Flow between concentric cylinders with the inner cylinder rotating and an axial pressure gradient imposed in the annulus reveals a rich variety of flow regimes depending on the flow conditions. The occurrence of these flow regimes was studied experimentally by both visually and optically detecting the transition from one flow regime to another over a wide(More)
The stability of supercritical Couette flow has been studied extensively, but few measurements of the velocity field of flow have been made. Particle image velocimetry (PIV) was used to measure the axial and radial velocities in a meridional plane for non-wavy and wavy Taylor–Couette flow in the annulus between a rotating inner cylinder and a fixed outer(More)
Granular flow in a rotating tumbler is of theoretical and industrial significance. However, in spite of its relative simplicity, little is known about the dynamics of the top flowing layer. Here we present an experimental study of the velocity field within the fluidized layer of monodisperse particles in a quasi-2D ͑two-dimensional͒ rotating tumbler in the(More)
We consider the impact of the effective gravitational acceleration g{eff} on gravity-driven granular shear flow utilizing a tumbler of radius R rotating at angular velocity omega when g{eff} is varied up to 25 times the gravitational level on Earth in a large centrifuge. The Froude number Fr=omega{2}R/g{eff} is shown to be the proper scaling to characterize(More)
Reverse osmosis (RO) is a compact process that has potential for the removal of ionic and organic pollutants for recycling space mission wastewater. Seven candidate RO membranes were compared using a batch stirred cell to determine the membrane flux and the solute rejection for synthetic space mission wastewaters. Even though the urea molecule is larger(More)
We investigate the effect of nanoscale variations in the surface roughness of individual particles on macroscale granular flow characteristics. Experiments were conducted in circular rotating tumblers with smooth and rough 2 and 3 mm steel particles. The smooth beads had a rms surface roughness of approximately 30 to 60 nm; rough beads had a surface(More)
Imposing axial flow in the annulus and/or radial flow through the cylindrical walls in a Taylor– Couette system alters the stability of the flow. Theoretical methods and numerical simulations were used to determine the impact of imposed axial and radial flows, homogeneous in the axial direction, on the first transition of Taylor–Couette flow in the(More)
The fluctuating wall shear stress, wall pressure, and streamwise velocity were measured simultaneously in a cylindrical boundary layer at a momentum thickness Reynolds number of Re ␪ ϭ2160 and a boundary layer thickness to cylinder radius ratio of ␦/aϭ5 using a hot wire wall shear stress probe mounted just upstream of a hearing aid microphone and a hot wire(More)
The flow in the gap between an inner rotating cylinder concentric with an outer stationary cylinder with an imposed pressure-driven axial flow was studied experimentally using particle image velocimetry ͑PIV͒ in a meridional plane of the annulus. The radius ratio was ␩ϭ0.83 and the aspect ratio was ⌫ϭ47. Velocity vector fields for nonwavy toroidal and(More)