Effect of Microstructure Geometric Form on Surface Shear Stress

2016 ◽  
Vol 139 (1) ◽  
Author(s):  
Kaushik K. Rangharajan ◽  
Matthew J. Gerber ◽  
Shaurya Prakash
Keyword(s):  
Reynolds Number ◽  
Shear Stress ◽  
High Surface ◽  
Cross Flow ◽  
Shear Stresses ◽  
Surface Shear Stress ◽  
Geometric Form ◽  
Incident Flow ◽  
Surface Shear ◽  
Reynolds Number Flow

Low Reynolds number flow of liquids over micron-sized structures and the control of subsequently induced shear stress are critical for the performance and functionality of many different microfluidic platforms that are extensively used in present day lab-on-a-chip (LOC) domains. However, the role of geometric form in systematically altering surface shear on these microstructures remains poorly understood. In this study, 36 microstructures of diverse geometry were chosen, and the resultant overall and facet shear stresses were systematically characterized as a function of Reynolds number to provide a theoretical basis to design microstructures for a wide array of applications. Through a set of detailed numerical calculations over a broad parametric space, it was found that the top facet (with respect to incident flow) of the noncylindrical microstructures experiences the largest surface shear stress. By systematically studying the variation of the physical dimensions of the microstructures and the angle of incident flow, a comprehensive regime map was developed for low to high surface shear structures and compared against the widely studied right circular cylinder in cross flow.

A Numerical Study for Biomimetic Structures to Control Wall Shear Stress in Water

2013 ◽  
Author(s):  
Matthew J. Gerber
Keyword(s):  
Shear Stress ◽  
Microbial Fuel Cells ◽  
Numerical Study ◽  
Strong Dependence ◽  
Control Surface ◽  
Shear Stresses ◽  
Surface Shear Stress ◽  
Surface Shear ◽  
Practical Applications ◽  
Biomimetic Structures

There are numerous practical applications whose operational efficiency depends on the shear stress (skin friction drag) on their functional surfaces, including artificial reefs, artificial hearts, and continuous flow microbial fuel cells. For the most part, the fundamental physics that govern surface shear stress are well understood and established, especially for relatively simple shapes such as a sphere or cylinder. However, the use of passive, bio-inspired, additive structures to control surface shear stress has thus far seen limited investigation. To evaluate the effect of geometrical forms on surface shear stress, 29 biomimetic structures based on sharkskin, cacti, and ocean-dwelling suspension feeders were studied. The structures were modeled in COMSOL Multiphysics, and the shear stresses on their surfaces were studied. The results show that shear stress on the surface of a structure depends not only on surface area, but also on the general form of the structure. In addition, the surface shear stress of some structures display a strong dependence on fluid-flow orientation, while others do not.

scholarly journals A process-based method for predicting lateral erosion rates

2021 ◽  
Author(s):  
Myron van Damme
Keyword(s):  
Soil Mechanics ◽  
High Surface ◽  
Shear Stresses ◽  
Empirical Equations ◽  
Predictive Capability ◽  
Surface Shear ◽  
Erosion Rates ◽  
Material Texture ◽  
Empirical Coefficients ◽  
The Impact

AbstractAn accurate means of predicting erosion rates is essential to improve the predictive capability of breach models. During breach growth, erosion rates are often determined with empirical equations. The predictive capability of empirical equations is governed by the range for which they have been validated and the accuracy with which empirical coefficients can be established. Most empirical equations thereby do not account for the impact of material texture, moisture content, and compaction energy on the erosion rates. The method presented in this paper acknowledges the impact of these parameters by accounting for the process of dilation during erosion. The paper shows how, given high surface shear stresses, the erosion rate can be quantified by applying the principles of soil mechanics. Key is thereby to identify that stress balance situation for which the dilatency induced inflow gives a maximum averaged shear resistance. The effectiveness of the model in predicting erosion rates is indicated by means of three validation test cases. A sensitivity analysis of the method is also provided to show that the predictions lie within the range of inaccuracy of the input parameters.

Visualization of separation and reattachment in an incident shock-induced interaction

2021 ◽  
pp. 095441002098349
Author(s):  
Yun Jiao ◽  
Chengpeng Wang
Keyword(s):  
Numerical Simulation ◽  
Shock Wave ◽  
Shear Stress ◽  
Separation Bubble ◽  
Incident Shock ◽  
Incident Shock Wave ◽  
Bottom Wall ◽  
Surface Shear Stress ◽  
Surface Shear ◽  
Oil Flow

An experimental study is conducted on the qualitative visualization of the flow field in separation and reattachment flows induced by an incident shock interaction by several techniques including shear-sensitive liquid crystal coating (SSLCC), oil flow, schlieren, and numerical simulation. The incident shock wave is generated by a wedge in a Mach 2.7 duct flow, where the strength of the interaction is varied from weak to moderate by changing the angle of attack α of the wedge from 8° and 10° to 12°. The stagnation pressure upstream was set to approximately 607.9 kPa. The SSLCC technique was used to visualize the surface flow characteristics and analyze the surface shear stress fields induced by the initial incident shock wave over the bottom wall and sidewall experimentally which resolution is 3500 × 200 pixels, and the numerical simulation was also performed as the supplement for a clearer understanding to the flow field. As a result, surface shear stress over the bottom wall was visualized qualitatively by SSLCC images, and flow features such as separation/reattachment and the variations of position/size of separation bubble with wedge angle were successfully distinguished. Furthermore, analysis of shear stress trend over the bottom wall by a hue value curve indicated that the relative magnitude of shear stress increased significantly downstream of the separation bubble compared with that upstream. The variation trend of shear stress was consistent with the numerical simulation results, and the error of separation position was less than 2 mm. Finally, the three-dimensional schematic of incident shock-induced interaction has been achieved by qualitative summary by multiple techniques, including SSLCC, oil flow, schlieren, and numerical simulation.

Measurement of surface shear stress vectors using liquid crystal coatings

AIAA Journal ◽  
1994 ◽  
Vol 32 (8) ◽  
pp. 1576-1582 ◽  
Author(s):  
Daniel C. Reda ◽  
Joseph J. Muratore
Keyword(s):  
Shear Stress ◽  
Liquid Crystal ◽  
Surface Shear Stress ◽  
Surface Shear

Seismic interpretation theory for an elastic earth

1954 ◽  
Vol 224 (1156) ◽  
pp. 43-63 ◽  
Keyword(s):  
Shear Stress ◽  
Seismic Interpretation ◽  
Elastic Theory ◽  
Static Case ◽  
Surface Shear Stress ◽  
Elastic Parameters ◽  
Surface Shear ◽  
Special Cases ◽  
Present Solution ◽  
Ray Path

The seismic interpretation problem for an isotropic spherical earth is analyzed on the basis of elastic theory, under the assumption that the three independent elastic parameters are unknown continuous functions of the depth. It is shown that solutions for these functions may be obtained in the form of Taylor’s series. The problem is treated for three types of symmetrical excitation conditions on the free surface: (1) a shear source of type p rϕ only; (2) a pressure distribution with vanishing surface shear stress; (3) an excitation consisting of pressure in combination with surface shear stress of type p rθ . In each case the excitation functions are arbitrary functions of time. It is assumed that the associated components of surface displacement over the sphere are known from available observations, as functions of time. Thus, the complete information contained in seismic records is used in the proposed interpretation process, without need of selecting, identifying and assigning arrival times to specific events on the records. The two static elastic parameters may theoretically be determined from observations at a single frequency, including the frequency zero, or static case. The determination of the dynamic elastic parameter requires the use of at least two frequencies. Algebraic checks are obtained by comparing the general solutions with the corresponding results for two special cases in which the elastic parameters vary in a prescribed manner in the interior of the sphere. In both these cases treatment by the classical ray-path method of interpretation is excluded, because the wave velocity decreases with depth. Furthermore, the ray-path method (which is essentially a method of geometrical optics) would fail to distinguish between the two examples in any case, since the velocity function is the same in both, although the elastic parameters differ. In contrast to the valuable ray-path method, the analytical procedures in the present solution of the elastic problem are prohibitively cumbersome. Practical application of elastic theory to the direct interpretation of seismograms requires further development of the theory with probable utilization of modern high-speed computing methods.

The Effects of Localized Blade Endwall Suction on Secondary Flows and Heat Transfer

2010 ◽  
Author(s):  
Rebecca Hollis ◽  
Jeffrey P. Bons
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
High Surface ◽  
Surface Heat ◽  
Secondary Flows ◽  
Surface Shear Stress ◽  
Mean Velocity ◽  
Surface Shear ◽  
Surface Heat Transfer ◽  
High Heat Transfer

Two methods of flow control were designed to mitigate the effects of the horseshoe vortex structure (HV) at an airfoil/endwall junction. An experimental study was conducted to quantify the effects of localized boundary layer removal on surface heat transfer in a low-speed wind tunnel. A transient infrared technique was used to measure the convective heat transfer values along the surface surrounding the juncture. Particle image velocimetry was used to collect the time-mean velocity vectors of the flow field across three planes of interest. Boundary layer suction was applied through a thin slot cut into the leading edge of the airfoil at two locations. The first, referred to as Method 1, was directly along the endwall, the second, Method 2, was located at a height ∼1/3 of the approaching boundary layer height. Five suction rates were tested; 0%, 6.5%, 11%, 15% and 20% of the approaching boundary layer mass flow was removed at a constant rate. Both methods reduced the effects of the HV with increasing suction on the symmetry, 0.5-D and 1-D planes. Method 2 yielded a greater reduction in surface heat transfer but Method 1 outperformed Method 2 aerodynamically by completely removing the HV structure when 11% suction was applied. This method however produced other adverse effects such as high surface shear stress and localized areas of high heat transfer near the slot edges at high suction rates.

The Effect Mechanism of Hydrodynamic Factors on Naphthenic Acid Flow-Induced Corrosion

2019 ◽  
Author(s):  
Yunrong Lyu
Keyword(s):  
Shear Stress ◽  
Turbulence Intensity ◽  
Naphthenic Acid ◽  
Wall Turbulence ◽  
Surface Shear Stress ◽  
Surface Shear ◽  
Flow Induced Corrosion ◽  
Velocity Flow ◽  
Near Wall Turbulence ◽  
Hydrodynamic Factors

Abstract Hydrodynamic factors are the important factors affecting the flow-induced corrosion of naphthenic acid. The effect mechanisms of hydrodynamic factors such as flow velocity, flow pattern, erosion angle and multiphase flow, etc. on the flow-induced corrosion of naphthenic acid are analyzed comprehensively, and the effect mechanisms of critical hydrodynamic parameters such as surface shear stress and near-wall turbulence intensity, etc. on naphthenic acid corrosion are explained. It is pointed out that in the flow-induced corrosion system of naphthenic acid, hydrodynamic factors such as flow velocity, flow pattern, erosion angle and multiphase flow, etc. influence the erosion intensity and mass transfer process generally by changing the magnitude of surface shear stress and near-wall turbulence intensity, thus affecting the severity of corrosion.

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