Irreversibility Equivalence Ratio of Micropatterned Surface Roughness for Wall Slip Flow Control

2007 ◽  
Author(s):  
Greg Naterer
Keyword(s):  
Surface Roughness ◽  
Flow Control ◽  
Equivalence Ratio ◽  
Slip Flow ◽  
Wall Slip

Steady Vortex-Generator Jet Flow Control on a Highly Loaded Transonic Low-Pressure Turbine Cascade: Effects of Compressibility and Roughness

2014 ◽  
Vol 136 (11) ◽  
Author(s):  
Chiara Bernardini ◽  
Stuart I. Benton ◽  
John D. Lee ◽  
Jeffrey P. Bons ◽  
Jen-Ping Chen ◽  
...  
Keyword(s):  
Surface Roughness ◽  
Mach Number ◽  
Flow Control ◽  
High Speed ◽  
Vortex Generator ◽  
Control Performance ◽  
Low Pressure Turbine ◽  
Blowing Ratio ◽  
Turbulent Separation ◽  
Mach Number Distribution

A new high-speed linear cascade has been developed for low-pressure turbine (LPT) studies at The Ohio State University. A compressible LPT profile is tested in the facility and its baseline performance at different operating conditions is assessed by means of isentropic Mach number distribution and wake total pressure losses. Active flow control is implemented through a spanwise row of vortex-generator jets (VGJs) located at 60% chord on the suction surface. The purpose of the study is to document the effectiveness of VGJ flow control in high-speed compressible flow. The effect on shock-induced separation is assessed by Mach number distribution, wake loss surveys and shadowgraph. Pressure sensitive paint (PSP) is applied to understand the three dimensional flow and shock pattern developing from the interaction of the skewed jets and the main flow. Data show that with increasing blowing ratio, the losses are first decreased due to separation reduction, but losses connected to compressibility effects become stronger due to increased passage shock strength and jet orifice choking; therefore, the optimum blowing ratio is a tradeoff between these counteracting effects. The effect of added surface roughness on the uncontrolled flow and on flow control behavior is also investigated. At lower Mach number, turbulent separation develops on the rough surface and a different flow control performance is observed. Steady VGJs appear to have control authority even on a turbulent separation but higher blowing ratios are required compared to incompressible flow experiments reported elsewhere. Overall, the results show a high sensitivity of steady VGJs control performance and optimum blowing ratio to compressibility and surface roughness.

Unsteady Flow of Power Law Fluids With Wall Slip in Microducts

2019 ◽  
Vol 141 (8) ◽  
Author(s):  
F. Talay Akyildiz ◽  
Dennis A. Siginer ◽  
M'hamed Boutaous
Keyword(s):  
Power Law ◽  
Nonlinear Partial Differential Equation ◽  
Slip Flow ◽  
Wall Slip ◽  
Nonlinear Boundary Conditions ◽  
Velocity Profiles ◽  
Momentum Balance ◽  
Power Law Fluids ◽  
Power Law Index ◽  
Pseudo Spectral

Unsteady laminar nonlinear slip flow of power law fluids in a microchannel is investigated. The nonlinear partial differential equation resulting from the momentum balance is solved with linear as well as nonlinear boundary conditions at the channel wall. We prove the existence of the weak solution, develop a semi-analytical solution based on the pseudo-spectral-Galerkin and Tau methods, and discuss the influence and effect of the slip coefficient and power law index on the time-dependent velocity profiles. Larger slip at the wall generates increased velocity profiles, and this effect is further enhanced by increasing the power law index. Comparatively, the velocity of the Newtonian fluid is larger and smaller than that of the power law fluid for the same value of the slippage coefficient if the power index is smaller and larger, respectively, than one.

Effects of Wall Slip on Convective Heat Transfers of Giesekus Fluid in Microannulus

2020 ◽  
Vol 142 (8) ◽  
Author(s):  
Mehdi Moayed Mohseni ◽  
Gilles Tissot ◽  
Michael Badawi
Keyword(s):  
Heat Transfer ◽  
Shear Stress ◽  
Convective Heat ◽  
Slip Flow ◽  
Critical Shear Stress ◽  
Wall Slip ◽  
Outer Wall ◽  
Bulk Temperature ◽  
Brinkman Number ◽  
Thermal Boundary Conditions

Abstract Convective heat transfer and effect of nonlinear wall slip are studied analytically in concentric microannulus for viscoelastic fluids obeying the Giesekus constitutive equation. Laminar, thermally, and hydrodynamically fully developed flow is considered. A nonlinear Navier model with nonzero slip critical shear stress is employed for the slip equation at both walls. Critical shear stress will cause three slip flow regimes: no slip condition, slip only at the inner wall, and slip at both walls. Thermal boundary conditions are assumed to be peripherally and axially constant fluxes at the walls. Governing equations are solved to obtain temperature profiles and Nusselt number and effects of slip parameters, elasticity, and Brinkman number are discussed. Two regimes are compared when slip occurs at both walls or only at the inner wall. The results indicate that by increasing slip effect and elasticity, heat transfer between wall and fluid is enhanced, but it decreases by increasing Brinkman number. In the case where the heat flux is dominant in the outer wall, the inner wall Nusselt curve shows a singularity for a critical Brinkman number because at this Brinkman number the bulk temperature will be equal to the wall temperature.

scholarly journals Acoustics with wall-slip flow of gas-saturated porous media

2004 ◽  
Vol 31 (3) ◽  
pp. 277-286 ◽  
Author(s):  
J. Chastanet ◽  
P. Royer ◽  
J.-L. Auriault
Keyword(s):  
Porous Media ◽  
Slip Flow ◽  
Wall Slip ◽  
Saturated Porous Media

Roughness Effect on the Heat Transfer Coefficient for Gaseous Flow in Microchannels

2010 ◽  
Author(s):  
Metin B. Turgay ◽  
Almila G. Yazicioglu ◽  
Sadik Kakac
Keyword(s):  
Heat Transfer ◽  
Surface Roughness ◽  
Nusselt Number ◽  
Flow Regime ◽  
Viscous Dissipation ◽  
Slip Flow ◽  
Roughness Height ◽  
Working Fluid ◽  
Axial Conduction ◽  
Slip Flow Regime

Effects of surface roughness, axial conduction, viscous dissipation, and rarefaction on heat transfer in a two–dimensional parallel plate microchannel with constant wall temperature are investigated numerically. Roughness is simulated by adding equilateral triangular obstructions with various heights on one of the plates. Air, with constant thermophysical properties, is chosen as the working fluid, and laminar, single-phase, developing flow in the slip flow regime at steady state is analyzed. Governing equations are solved by finite element method with tangential slip velocity and temperature jump boundary conditions to observe the rarefaction effect in the microchannel. Viscous dissipation effect is analyzed by changing the Brinkman number, and the axial conduction effect is analyzed by neglecting and including the corresponding term in the energy equation separately. Then, the effect of surface roughness on the Nusselt number is observed by comparing with the corresponding smooth channel results. It is found that Nusselt number decreases in the continuum case with the presence of surface roughness, while it increases with increasing roughness height in the slip flow regime, which is also more pronounced at low-rarefied flows (i.e., around Kn = 0.02). Moreover, the presence of axial conduction and viscous dissipation has increasing effects on heat transfer with increasing roughness height. Even in low velocity flows, roughness increases Nusselt number up to 33% when viscous dissipation is considered.

Slip due to Rarefaction, Surface Roughness, and Intermolecular Interactions for Gases and Liquids

2011 ◽  
Author(s):  
Phil Ligrani
Keyword(s):  
Surface Roughness ◽  
Intermolecular Interactions ◽  
Stokes Equations ◽  
Slip Length ◽  
Wall Slip ◽  
Mean Free Path ◽  
Working Fluid ◽  
Channel Height ◽  
Near Surface ◽  
Accommodation Coefficients

In the present study, slip phenomena are investigated in two different sets of experiments conducted in gases and one Newtonian liquid. Overall, differences in near-surface slip behavior are illustrated for these two different fluid mediums, where the slip is induced surface roughness and rarefaction in the gases, and by surface roughness and intermolecular interactions in the liquid. Within both sets of experiments, flows are induced within micro-fluidic passages by rotation within C-shaped fluid chambers formed between a rotating disk and a stationary surface. When gases are employed, accommodation coefficients are determined in a unique manner from experimental results and analysis based on the Navier-Stokes equations. In all cases, roughness size is large compared to molecular mean free path. When channel height is defined at the tops of the roughness elements, slip is believed to be a result of rarefaction as well as fluid shear. With this arrangement, tangential accommodation coefficients decrease and slip velocity magnitudes increase, at a particular value of Knudsen number, as the level of surface roughness increases. With Newtonian water as the working fluid, hydrophobic roughness is used to induce near-wall slip in the fluid chamber. The magnitudes of slip length and slip velocities increase as the average size of the surface roughness becomes larger. The resulting slip length data show a high degree of organization when normalized using the fluid chamber height, such that experimental data obtained using different chamber heights and different disk roughness magnitudes collapse along a single line, illustrating strong linear dependence of the slip length on the normalized radial-line-averaged shear stress.

Hydrothermal performance analysis of various surface roughness configurations in trapezoidal microchannels at slip flow regime

2020 ◽  
Vol 28 (6) ◽  
pp. 1522-1532 ◽  
Author(s):  
Davood Toghraie ◽  
Ramin Mashayekhi ◽  
Mohammadreza Niknejadi ◽  
Hossein Arasteh
Keyword(s):  
Surface Roughness ◽  
Performance Analysis ◽  
Flow Regime ◽  
Slip Flow ◽  
Slip Flow Regime
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