Passive Bristling of Shark Skin Scales at the Micro-Level: A Fundamental Viscous Flow Study to Understand the Separation Control Mechanism

2020 ◽  
Author(s):  
Reid Prichard ◽  
Wayne Strasser ◽  
Chad Cherok ◽  
Robert Kacinski ◽  
Amy Lang
Keyword(s):  
Control Mechanism ◽  
Adverse Pressure Gradient ◽  
Viscous Sublayer ◽  
Cfd Analysis ◽  
Mako Shark ◽  
Fluid Properties ◽  
Micro Level ◽  
Zero Net Mass Flux ◽  
Incipient Separation ◽  
Flow Study

Abstract In this paper, we use a CFD analysis of a simplified, 2D geometry to study the ability of mako shark denticles to mitigate flow separation. We represent the viscous sublayer below a turbulent boundary layer streak as a Couette flow. Incipient separation is simulated by balancing upper wall velocity and adverse pressure gradient to achieve zero net mass flow, and we add various denticle geometries to study their effects. Each modeled denticle protrudes at an angle from 15° to 85° and sublayer blockage ratio from 0.05 to 0.85. Through variation of fluid properties and boundary conditions, we show that the anti-flow-reversal abilities of a single, bristled shark denticle are independent of Reynolds number, and we investigate the effect of the denticle at cases other than zero net mass flux. Based on these results, we create a new relationship to predict separation inhibition. These conclusions are highly generalizable and represent previously undiscovered universal behavior.

Compensation of Pressure Peaks in PWK-Type Hydraulic Pumps

2011 ◽  
Vol 490 ◽  
pp. 33-44 ◽  
Author(s):  
Leszek Osiecki ◽  
Piotr Patrosz ◽  
Tomasz Zawistowski ◽  
Bettina Landvogt ◽  
Janusz Piechna ◽  
...  
Keyword(s):  
High Speed ◽  
High Efficiency ◽  
Control Mechanism ◽  
Direct Action ◽  
Cfd Analysis ◽  
Ability To Work ◽  
University Of Technology ◽  
Axial Pumps ◽  
Variable Displacement ◽  
Compensation Chamber

Hydraulic axial pumps equipped with cam-driven commutation unit (PWK pumps) proved their high efficiency up to 55 MPa and ability to work self-sucking, even at high speed. Displacement of PWK pump may easily be changed by moving its control cam. Full discharge from hydrostatic forces makes such control possible by direct action of a low-energy actuator like proportional electromagnet or stepping motor. That eliminates heavy and costly hydraulic servomechanism, necessary in other variable displacement machines. Such a control mechanism was positively evaluated in prototype tests in Department of Hydraulics and Pneumatics of Gdańsk University of Technology. The new commutation unit generates however harmful pressure peaks. The paper presents the compensation method for pressure peaks by use of the elastic compensation chamber. It shows also results of multidisciplinary FEA and CFD analysis necessary to properly design the compensation chamber.

Turbulent Boundary Layer with Pressure Gradient Alternating in Sign

1976 ◽  
Vol 27 (1) ◽  
pp. 15-28 ◽  
Author(s):  
Yutaka Tsuji ◽  
Yoshinobu Morikawa
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Pressure Gradient ◽  
Adverse Pressure Gradient ◽  
Turbulent Energy ◽  
Viscous Sublayer ◽  
Internal Boundary Layer ◽  
Internal Boundary ◽  
Pressure Gradients ◽  
Logarithmic Law

SummaryAn experiment was made on a turbulent boundary layer with adverse and favourable pressure gradients alternating twice along the stream. The most important findings of the present study are as follows. In the region of the adverse pressure gradient downstream of the strong acceleration, an internal boundary layer develops within the boundary layer. In this internal layer large advection of turbulent energy occurs and the flow is locally non-equilibrium even near the wall. As a result the usual logarithmic law and turbulence similarity in the viscous sublayer break down.

scholarly journals Optimization of Vegetable Oil Properties in Machining Environment through CFD

2019 ◽  
Vol 8 (12) ◽  
pp. 644-649
Keyword(s):  
Thermal Conductivity ◽  
Specific Heat ◽  
Vegetable Oil ◽  
Vegetable Oils ◽  
Superior Performance ◽  
Cfd Analysis ◽  
Aisi 304 ◽  
Aisi 304 Steel ◽  
Fluid Properties

Various vegetable oils were widely used as a lubricant in machining since 1990‘s. However during machining of various materials, various vegetable oils gave superior performance related to other oils which is due to their individual thermo physical properties. So that the prediction of influencing properties of various vegetable oils novel technique. Therefore in the present work turning of AISI 304 steel with carbide tool is taken as a case study for ascertaining the influence of vegetable oil properties in the machining environment. Among the fluid properties, properties such as viscosity, thermal conductivity, density and specific heat are taken for optimization. For optimization of fluid properties initially DOE Technique has been adopted, using which L16 orthogonal array has been formed for carrying out the simulations. CFD analysis with proper boundary conditions has been adopted for predictions the generated temperature at a constant distance from tool tip. From the obtained results, it is perceived that thermal conductivity is performed a major role to reducing of generated temperature within the tool followed by viscosity and specific heat whereas effect of density on generated temperature is found to be least significant. Therefore the present work highlights the combinations of DOE approach and CFD analysis in predicting the influence of vegetable oil properties and their values in the machining environment

The effect of pressure gradient on the law of the wall in turbulent flow

1969 ◽  
Vol 35 (2) ◽  
pp. 311-336 ◽  
Author(s):  
Henry Mcdonald
Keyword(s):  
Velocity Profile ◽  
Turbulent Flow ◽  
Pressure Gradient ◽  
Adverse Pressure Gradient ◽  
Viscous Sublayer ◽  
Measured Velocity ◽  
Law Of The Wall ◽  
Two Dimensional Flow ◽  
Streamwise Pressure Gradient ◽  
Total Shear Stress

The effect of a streamwise pressure gradient on the velocity profile in the viscous sublayer of a turbulent flow along a smooth wall in two-dimensional flow is estimated. In the analysis, a similarity argument is used and the necessary empirical information obtained from a constant pressure flow. An allowance is made for the departure from the wall value of the gradient of total shear stress normal to the wall. The results of analysis were used to generate new additive constants for use with Townsend's modified law of the wall velocity profile and subsequently Townsend's profile is found to be in good agreement with the measured velocity profiles in an adverse pressure gradient.

Role of the Cilia Membrane in Control of Microtubule Sliding

1980 ◽  
Vol 38 ◽  
pp. 612-615
Author(s):  
Edna S. Kaneshiro
Keyword(s):  
Control Mechanism ◽  
Beat Frequency ◽  
Surface Membrane ◽  
Ciliary Membrane ◽  
Ciliary Beating ◽  
Ciliary Reversal ◽  
Voltage Dependent ◽  
Reversal Mechanism ◽  
And Function

It is currently believed that ciliary beating results from microtubule sliding which is restricted in regions to cause bending. Cilia beat can be modified to bring about changes in beat frequency, cessation of beat and reversal in beat direction. In ciliated protozoans these modifications which determine swimming behavior have been shown to be related to intracellular (intraciliary) Ca2+ concentrations. The Ca2+ levels are in turn governed by the surface ciliary membrane which exhibits increased Ca2+ conductance (permeability) in response to depolarization. Mutants with altered behaviors have been isolated. Pawn mutants fail to exhibit reversal of the effective stroke of ciliary beat and therefore cannot swim backward. They lack the increased inward Ca2+ current in response to depolarizing stimuli. Both normal and pawn Paramecium made leaky to Ca2+ by Triton extrac¬tion of the surface membrane exhibit backward swimming only in reactivating solutions containing greater than IO-6 M Ca2+ Thus in pawns the ciliary reversal mechanism itself is left operational and only the control mechanism at the membrane is affected. The topographic location of voltage-dependent Ca2+ channels has been identified as a component of the ciliary mem¬brane since the inward Ca2+ conductance response is eliminated by deciliation and the return of the response occurs during cilia regeneration. Since the ciliary membrane has been impli¬cated in the control of Ca2+ levels in the cilium and therefore is the site of at least one kind of control of microtubule sliding, we have focused our attention on understanding the structure and function of the membrane.

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