On the Phenomenon of Separation During Compression and Frictional Sliding of an Elastic Rectangle

1976 ◽  
Vol 43 (2) ◽  
pp. 268-274
Author(s):  
S. Dasgupta ◽  
S. N. Prasad
Keyword(s):  
Shear Stress ◽  
Sliding Friction ◽  
Frictional Coefficient ◽  
Practical Interest ◽  
Compressive Force ◽  
Leading Edge ◽  
Coefficient Of Sliding Friction ◽  
Rigid Plane ◽  
Contact Shear Stress ◽  
Sliding Force

The plane strain compression and sliding of an elastic rectangle is considered whose one set of parallel edges are free from tractions. The remaining set of parallel edges is simultaneously subjected by rigid rough planes to a compressive force P and a sliding force F = μP, where μ is the coefficient of sliding friction. The rigid planes are prevented from rotation and a limiting equilibrium is assumed by taking the contact shear stress to be equal to the product of the normal compressive stress with μ. It is found that the presence of free edges significantly affects the deformation of the rectangle. In particular, it is shown that during sliding the leading edge of the rectangle is compressed most severely against the rigid plane, whereas separation takes place at the trailing edge. The separation occurs at the slightest trace of the application of load and although the magnitude depends upon the level of loading, the extent of the zone depends only on Poisson’s ratio, frictional coefficient, and the aspect ratio. Numerical results of the quantities of practical interest are reported.

Swept wing boundary-layer receptivity to localized surface roughness

2012 ◽  
Vol 711 ◽  
pp. 516-544 ◽  
Author(s):  
David Tempelmann ◽  
Lars-Uve Schrader ◽  
Ardeshir Hanifi ◽  
Luca Brandt ◽  
Dan S. Henningson
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Practical Interest ◽  
Leading Edge ◽  
Constant Factor ◽  
Computationally Efficient ◽  
Swept Wing ◽  
Predictive Tool ◽  
Free Stream Turbulence ◽  
Streamwise Location

AbstractThe receptivity to localized surface roughness of a swept-wing boundary layer is studied by direct numerical simulation (DNS) and computations using the parabolized stability equations (PSEs). The DNS is laid out to reproduce wind tunnel experiments performed by Saric and coworkers, where micron-sized cylinders were used to trigger steady crossflow modes. The amplitudes of the roughness-induced fundamental crossflow wave and its superharmonics obtained from nonlinear PSE solutions agree excellently with the DNS results. A receptivity model using the direct and adjoint PSEs is shown to provide reliable predictions of the receptivity to roughness cylinders of different heights and chordwise locations. Being robust and computationally efficient, the model is well suited as a predictive tool of receptivity in flows of practical interest. The crossflow mode amplitudes obtained based on both DNS and PSE methods are 40 % of those measured in the experiments. Additional comparisons between experimental and PSE data for various disturbance wavelengths reveal that the measured disturbance amplitudes are consistently larger than those predicted by the PSE-based receptivity model by a nearly constant factor. Supplementary DNS and PSE computations suggest that possible natural leading-edge roughness and free-stream turbulence in the experiments are unlikely to account for this discrepancy. It is more likely that experimental uncertainties in the streamwise location of the roughness array and cylinder height are responsible for the additional receptivity observed in the experiments.

scholarly journals Accurate Measurements of Wall Shear Stress on a Plate with Elliptic Leading Edge

Sensors ◽  
2018 ◽  
Vol 18 (8) ◽  
pp. 2682 ◽  
Author(s):  
Guang-Hui Ding ◽  
Bing-He Ma ◽  
Jin-Jun Deng ◽  
Wei-Zheng Yuan ◽  
Kang Liu
Keyword(s):  
Shear Stress ◽  
Wind Tunnel ◽  
Wall Shear Stress ◽  
Leading Edge ◽  
Reynold Number ◽  
Micro Electro Mechanical System ◽  
Flow Speed ◽  
Silicon On Insulator ◽  
Micro Sensor ◽  
Wall Shear

A micro-floating element wall shear stress sensor with backside connections has been developed for accurate measurements of wall shear stress under the turbulent boundary layer. The micro-sensor was designed and fabricated on a 10.16 cm SOI (Silicon on Insulator) wafer by MEMS (Micro-Electro-Mechanical System) processing technology. Then, it was calibrated by a wind tunnel setup over a range of 0 Pa to 65 Pa. The measurements of wall shear stress on a smooth plate were carried out in a 0.6 m × 0.6 m transonic wind tunnel. Flow speed ranges from 0.4 Ma to 0.8 Ma, with a corresponding Reynold number of 1.05 × 106~1.55 × 106 at the micro-sensor location. Wall shear stress measured by the micro-sensor has a range of about 34 Pa to 93 Pa, which is consistent with theoretical values. For comparisons, a Preston tube was also used to measure wall shear stress at the same time. The results show that wall shear stress obtained by three methods (the micro-sensor, a Preston tube, and theoretical results) are well agreed with each other.

Analysis of Laminar Mixed Convective Plumes Along Vertical Adiabatic Surfaces

1984 ◽  
Vol 106 (3) ◽  
pp. 552-557 ◽  
Author(s):  
K. V. Rao ◽  
B. F. Armaly ◽  
T. S. Chen
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Leading Edge ◽  
Vertical Surface ◽  
Stream Velocity ◽  
Thermal Source ◽  
Flow Conditions ◽  
Velocity Overshoot ◽  
Wall Shear ◽  
Prandtl Numbers

Laminar mixed forced and free convection from a line thermal source imbedded at the leading edge of an adiabatic vertical surface is analytically investigated for the cases of buoyancy assisting and buoyancy opposing flow conditions. Temperature and velocity distributions in the boundary layer adjacent to the adiabatic surface are presented for the entire range of the buoyancy parameter ξ (x) = Grx/Rex5/2 from the pure forced (ξ(x) = 0) to the pure free (ξ(x) = ∞) convection regime for fluids having Prandtl numbers of 0.7 and 7.0. For buoyancy-assisting flow, the velocity overshoot, the temperature, and the wall shear stress increase as the plume’s strength increases. On the other hand, the velocity overshoot, the wall shear stress, and the temperature decrease as the free-stream velocity increases. For buoyancy opposing flow, the velocity and wall shear stress decrease but the temperature increases as the plume’s strength increases.

An Experimental Study of Local Wall Shear Stress, Surface Static Pressure, and Flow Visualization Upstream, Alongside, and Downstream of a Blade Endwall Corner

1991 ◽  
Vol 113 (4) ◽  
pp. 626-632 ◽  
Author(s):  
A. K. Abdulla ◽  
R. K. Bhargava ◽  
R. Raj
Keyword(s):  
Experimental Study ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Flow Visualization ◽  
Static Pressure ◽  
Leading Edge ◽  
Chord Length ◽  
Corner Region ◽  
Wall Shear ◽  
Blade Leading Edge

The experimental study reported in this paper was performed to acquire information on the distribution of wall shear stress and surface static pressure in a blade endwall corner. The blade endwall corner region investigated was divided into three sections: 0.4 chord length upstream of the blade leading edge, inside the endwall corner region, and one chord length downstream of the blade trailing edge. The maximum increases in the values of wall shear stress were found to exist on the endwall, in the corner region, between the blade leading edge and the location of maximum blade thickness (≈ 140 percent maximum increase, compared to its far upstream value, at x/D = 6). Surface flow visualization defined the boundaries of the vortex system and provided information on the direction and magnitude of the wall shear stress. The acquired results indicated that the observed variations of wall shear stress and surface static pressure were significantly influenced by the interaction of secondary flows with pressure gradients induced by the presence of blade curvature.

Recent Investigations in Plastic Torsion

1937 ◽  
Vol 4 (4) ◽  
pp. A163-A169
Author(s):  
C. W. MacGregor ◽  
J. A. Hrones
Keyword(s):  
Shear Stress ◽  
Cross Sections ◽  
Maximum Shear Stress ◽  
Practical Interest ◽  
Modulus Of Rupture ◽  
Double Shear ◽  
Annealed Steel ◽  
Shearing Strain ◽  
Splined Shaft ◽  
Single Set

Abstract Tension, double-shear, and torsion tests on cast iron, S.A.E. 1045 annealed steel, and S.A.E. 1112 annealed steel are described in which the quantitative relations between the so-called modulus of rupture, double shear strength, and actual maximum shear stress in the bar at fracture are given for each material. The shear stress distribution over the cross section of each bar at fracture is also determined. Further, the data obtained from tension and torsion tests on the two steels are plotted on a single set of coordinates, namely the octahedral shearing stress τn and the octahedral shearing strain γn. A reasonable check is obtained between the two curves when the shear strain is less than that corresponding to the tensile strength. Finally, there is described a series of plastic-torsion tests on bars of mild steel with various new cross sections of practical interest, namely, the splined shaft, the circular shaft with two shallow rectangular keyways, double- and four-lipped drills, and I-beams. In these tests, the regions of initial yielding are determined by means of the Fry etching method.

scholarly journals Derivation of Ice Sliding Properties from The Numerical Modelling of Surging Ice Masses

1979 ◽  
Vol 23 (89) ◽  
pp. 420-421 ◽  
Author(s):  
W. F. Budd ◽  
B. J. McInnes ◽  
I. Smith
Keyword(s):  
Shear Stress ◽  
Numerical Modelling ◽  
Sliding Friction ◽  
Two Dimensional ◽  
Dimensional Model ◽  
Flow Properties ◽  
Two Dimensional Model ◽  
Two Parameters ◽  
Basal Shear ◽  
Best Fit

Abstract It is difficult to deduce sliding properties from the numerical modelling of ordinary glaciers because the flow law of ice is still not known well enough to clearly differentiate sliding from internal deformation of the ice. For glaciers undergoing high-speed surges it appears that the majority of the total speed is due to sliding. Furthermore the average basal shear stress of the ice mass is lowered during the surge. This suggests that surging glaciers can be modelled by incorporating a sliding friction law which has the effective friction coefficient decreasing for high velocities. A relation of this type has been found for ice sliding on granite at −0.5°C by Barnes and others (1971) and has also been obtained for rough slabs with ice at the pressure-melting point by Budd and others (1979). A simple two-dimensional model was developed by Budd and McInnes (1974) and Budd (1975), which was found to exhibit the typical periodic surge-like characteristics of real ice masses. Since the sliding-stress relation for the low velocities and stresses was not known, and was not so important for the surges, it was decided to use the condition of gross equilibrium (i.e. that the ice mass as a whole does not accelerate) together with a single-parameter relation for the way in which the friction decreases with stress and velocity to prescribe the basal shear-stress distribution. The low-stress-velocity relation can thus be obtained as a result. This two-dimensional model has now been parameterized to take account of the three-dimensional aspects of real ice masses. A number of ice masses have since been closely matched by the model including three well-known surging ice masses: Lednik Medvezhiy, Variegated Glacier, and Bruarjökull. Since the flow properties of ice are so poorly known—especially for longitudinal stress and strain-rates—the model has been run with two unknown parameters: one a flow-law parameter (η) and the other a sliding parameter (ø). The model is run over a wide range of these two parameters to see if a good match can be made to the real ice masses and if so what the values of the parameters η and ø are for best fit. The matching of the three above ice masses gave very similar values for each of the two parameters η and ø, the value of η being within the range of values expected for the flow properties of temperate ice as determined by laboratory experiments. Using the same values of η and ø it is found that the ordinary glaciers modelled so far do not develop surging but that they could do if the value of ø were increased or if the mass-balance input were sufficiently increased. For Lednik Medvezhiy a detailed analysis of the friction coefficient with velocity was carried out and it was found that the values required for best fit showed a very close agreement to the sliding friction curve of Barnes and others (1971) at −0.5°C. It is concluded that this type of sliding relation can account for the major features of glacier surge phenomena. Finally it is apparent that the numerical modelling technique can be used very effectively to test any large-scale bulk sliding relation by the analysis of real surges of ice masses and in addition can provide further insight into the sliding relation in association with other stresses in the ice mass.

Numerical Study of Impingement and Film Composite Cooling on Blade Leading Edge

2014 ◽  
Author(s):  
Zhao Liu ◽  
Lv Ye ◽  
Zhenping Feng
Keyword(s):  
Shear Stress ◽  
Nusselt Number ◽  
Numerical Study ◽  
Density Ratio ◽  
Leading Edge ◽  
Cooling Effectiveness ◽  
Simulation Accuracy ◽  
Film Composite ◽  
Blowing Ratio ◽  
Shear Stress Transport

In this paper a numerical study is performed to simulate the impingement and film composite cooling on the first stage rotor blade of GE-E3 engine high pressure turbine. A commercial CFD software CFX11.0 with a 3D RANS approach is adopted in the study. Firstly, by comparing with available experimental data, the relative performance of four turbulence models for numerical impingement and film composite cooling is studied, including the standard k-ε model, the RNG k-ε model, the standard k-ω model and the Shear-Stress Transport k-ω model. The Shear-Stress Transport k-ω model is chosen for the numerical study as it shows the best simulation accuracy. Then the simulations consist of five different density ratios (1.16∼4.81) and seven different blowing ratios (0.5∼3.0). The results indicate that the cooling effectiveness on pressure side is lower than that on the suction side. The cooling effectiveness increases with the increase of blowing ratio in the study range, but decreases with the increase of density ratio. On the target surface, the average Nusselt number, the circumferential averaged Nusselt number and its peak value increase with the increasing in blowing ratio, but decrease with the increase of density ratio.

CFD CHARACTERIZATION OF FLOW PATTERN AROUND ENDOTHELIAL CELL IN DENGUE INFECTION WITH PLASMA LEAKAGE

2015 ◽  
Vol 76 (7) ◽  
Author(s):  
Nur Kaliwantoro ◽  
Marsetyawan HNE Soesatyo ◽  
Indarto Indarto ◽  
Mohammad Juffrie ◽  
Rini Dharmastiti ◽  
...  
Keyword(s):  
Shear Stress ◽  
Endothelial Cell ◽  
Dengue Virus ◽  
Fluid Dynamic ◽  
Dengue Infection ◽  
Leading Edge ◽  
Cell Junction ◽  
Computational Domain ◽  
Permeable Membrane ◽  
Plasma Leakage

Plasma leakage is the pathological hall mark in dengue infection and may cause fatal condition to the patients. In this paper, the CFD (computational fluid dynamic) model is adopted to characterize the flow on the endothelial cells surface with plasma leakage based on in vitro experiments of HUVEC (human umbilical vein endothelial cell) culture on the permeable membrane. The computational domain used is a simplified model of single cell. At the leading edge of the domain and among the membranes, the gaps are modeled as a representation of cell-cell junction breakdown caused by dengue virus infection.  The result shows that at the leading edge , the fluid starts to move more quickly and increases to the maximum value at the middle of the cell and then drops to zero at the trailing edge. From the physical point of view, this result describes that there is a variation of the values of the wall shear stress due to the velocity gradient. These results can be considered as a first step to develop the ways of the prevention of the dengue infection through manipulation the shear stress to reduce the potency of dengue virus to attach the cell surface.  

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