Regimes of flow through cylinder arrays subject to steady pressure gradients

2020 ◽  
Vol 159 ◽  
pp. 120072
Author(s):  
Zahra Khalifa ◽  
Liam Pocher ◽  
Nils Tilton
Keyword(s):  
Pressure Gradients ◽  
Steady Pressure ◽  
Cylinder Arrays ◽  
Flow Through

scholarly journals The structure and dynamics of patch-clamped membranes: a study using differential interference contrast light microscopy.

1990 ◽  
Vol 111 (2) ◽  
pp. 599-606 ◽  
Author(s):  
M Sokabe ◽  
F Sachs
Keyword(s):  
Cell Surface ◽  
Transmural Pressure ◽  
Positive Pressure ◽  
Radius Of Curvature ◽  
Pressure Gradients ◽  
Structure And Motion ◽  
Excised Patches ◽  
Glass Interface ◽  
Pipette Tip ◽  
Flow Through

We have developed techniques for micromanipulation under high power video microscopy. We have used these to study the structure and motion of patch-clamped membranes when driven by pressure steps. Patch-clamped membranes do not consist of just a membrane, but rather a plug of membrane-covered cytoplasm. There are organelles and vesicles within the cytoplasm in the pipette tip of both cell-attached and excised patches. The cytoplasm is capable of active contraction normal to the plane of the membrane. With suction applied before seal formation, vesicles may be swept from the cell surface by shear stress generated from the flow of saline over the cell surface. In this case, patch recordings are made from membrane that was not originally present under the tip. The vesicles may break, or fuse and break, to form the gigasealed patch. Patch membranes adhere strongly to the wall of the pipette so that at zero transmural pressure the membranes tend to be normal to the wall. With transmural pressure gradients, the membranes generally become spherical; the radius of curvature decreasing with increasing pressure. Some patches have nonuniform curvature demonstrating that forces normal to the membrane may be significant. Membranes often do not respond quickly to changes in pipette pressure, probably because viscoelastic cytoplasm reduces the rate of flow through the tip of the pipette. Inside-out patches may be peeled from the walls of the pipette, and even everted (with positive pressure), without losing the seal. This suggests that the gigaseal is a distributed property of the membrane-glass interface.

Contribution of the large hepatic veins to postsinusoidal vascular resistance

1992 ◽  
Vol 262 (1) ◽  
pp. G14-G22 ◽  
Author(s):  
R. Maass-Moreno ◽  
C. F. Rothe
Keyword(s):  
Transition Point ◽  
Venous Pressure ◽  
Primary Site ◽  
The Other ◽  
Hepatic Veins ◽  
Pressure Gradients ◽  
Double Lumen ◽  
Pentobarbital Sodium ◽  
Anesthetized Dogs ◽  
Flow Through

We tested the hypothesis that the larger (greater than 2 mm ID) hepatic veins are the primary site of the portal-to-caval venous pressure gradient in the dog. Double-lumen catheters were inserted through the caval wall into hepatic veins of pentobarbital sodium-anesthetized dogs. One lumen opened at the end, and the other to the side. Each catheter was advanced until stopped and then it was withdrawn. The pressure at either port dropped from 87 +/- 31 to 13 +/- 11% of the portal-to-caval pressure difference as each moved past a transition point (TP). The location of the TP depended on the catheter diameter. Intraportal histamine or norepinephrine, 4 and 2.6 micrograms.min-1.kg body wt-1 respectively, augmented only the pressure measured upstream to the TP. A mathematical model of flow through a vessel with a catheter inside predicted a marked increase in resistance when the ratio of catheter OD to vessel ID exceeded approximately 0.6. Autopsy revealed ratios greater than 0.6 upstream to the TP. A hydraulic model confirmed that this effect caused the appearance of the TP. Given the depth (11.7 cm) at which near caval pressures could be found, even during histamine administration, we conclude that the major pressure gradients in the canine liver must lie upstream to the large hepatic veins.

scholarly journals Effects of Wall Ventilation on the Shock-wave/Viscous-Layer Interactions in a Mach 2.2 Intake

Processes ◽  
2020 ◽  
Vol 8 (2) ◽  
pp. 208 ◽  
Author(s):  
Humrutha Gunasekaran ◽  
Thillaikumar Thangaraj ◽  
Tamal Jana ◽  
Mrinal Kaushik
Keyword(s):  
High Speed ◽  
Static Pressure ◽  
Normal Shock ◽  
Pressure Gradients ◽  
Dual Mode ◽  
Contraction Ratio ◽  
Cavity Configuration ◽  
Flow Through ◽  
Flow Compressor ◽  
Surface Covering

In order to achieve proficient combustion with the present technologies, the flow through an aircraft intake operating at supersonic and hypersonic Mach numbers must be decelerated to a low-subsonic level before entering the combustion chamber. High-speed intakes are generally designed to act as a flow compressor even in the absence of mechanical compressors. The reduction in flow velocity is essentially achieved by generating a series of oblique as well as normal shock waves in the external ramp region and also in the internal isolator region of the intake. Thus, these intakes are also referred to as mixed-compression intakes. Nevertheless, the benefits of shock-generated compression do not arise independently but with enormous losses because of the shockwave and boundary layer interactions (SBLIs). These interactions should be manipulated to minimize or alleviate the losses. In the present investigation a wall ventilation using a new cavity configuration (having a cross-section similar to a truncated rectangle with the top wall covered by a thin perforated surface is deployed underneath the cowl-shock impinging point of the Mach 2.2 mixed-compression intake. The intake is tested for four different contraction ratios of 1.16, 1.19, 1.22, and 1.25, with emphasis on the effect of porosity, which is varied at 10.6%, 15.7%, 18.8%, and 22.5%. The introduction of porosity on the surface covering the cavity has been proved to be beneficial in decreasing the wall static pressure substantially as compared to the plain intake. A maximum of approximately 24.2% in the reduction in pressure at the upstream proximal location of 0.48 L is achieved in the case of the wall-ventilated intake with 18.8% porosity, at the contraction ratio of 1.19. The Schlieren density field images confirm the efficacy of the 18.8% ventilation in stretching the shock trains and in decreasing the separation length. At the contraction ratios of 1.19, 1.22, and 1.25 (‘dual-mode’ contraction ratios), the controlled intakes with higher porosity reduce the pressure gradients across the shockwaves and thereby yields an ‘intake-start’ condition. However, for the uncontrolled intake, the ‘unstart’ condition emerges due to the formation of a normal shock at the cowl lip. Additionally, the cowl shock in the ‘unstart’ intake is shifted upstream because of higher downstream pressure.

Simulations of coastal upwelling on the Sydney Continental Shelf

2000 ◽  
Vol 51 (6) ◽  
pp. 577 ◽  
Author(s):  
Patrick Marchesiello ◽  
Mark T. Gibbs ◽  
Jason H. Middleton
Keyword(s):  
Boundary Layer ◽  
Coastal Upwelling ◽  
Deep Ocean ◽  
Bottom Boundary Layer ◽  
Return Flow ◽  
Pressure Gradients ◽  
Bottom Boundary ◽  
Eastern Australia ◽  
Flow Through ◽  
Good Agreement

Two-dimensional numerical simulations of the response of the coastal waters of Sydney, south-eastern Australia, to idealized upwelling-favourable winds are presented. The spin up of the upwelling circulation is investigated, in particular the structure of the nearshore circulation. The intensity of the final upwelling state is found to be strongly linked to the activation of the return flow through the bottom boundary layer, which is also related to the strength of imposed alongshore pressure gradients. Results from a simulation of upwelling forced by a deep-ocean alongshore-current jet also show the final upwelling state to be weak in comparison with upwelling states produced by the action of the local wind stress. Bottom boundary layer shut-down in the presence of such a forcing jet is also discussed. A simulation of a real upwelling event was also performed and good agreement was found between the simulation and observations from a field experiment performed during summer 1994 in the Sydney coastal ocean.

scholarly journals Osmotic Flow of Water across Permeable Cellulose Membranes

1960 ◽  
Vol 44 (2) ◽  
pp. 315-326 ◽  
Author(s):  
Richard P. Durbin
Keyword(s):  
Hydrostatic Pressure ◽  
Biological Membrane ◽  
Volume Flow ◽  
Osmotic Gradient ◽  
Pressure Gradients ◽  
Deuterated Water ◽  
Direct Measurements ◽  
Flow Through ◽  
Cellulose Membranes ◽  
Effective Pore Radius

Direct measurements have been made of the net volume flow through cellulose membranes, due to a difference in concentration of solute across the membrane. The aqueous solutions used included solutes ranging in size from deuterated water to bovine serum albumin. For the semipermeable membrane (impermeable to the solute) the volume flow produced by the osmotic gradient is equal to the flow produced by the hydrostatic pressure RT ΔC, as given by the van't Hoff relationship. In the case in which the membrane is permeable to the solute, the net volume flow is reduced, as predicted by the theory of Staverman, based on the thermodynamics of the steady state. A means of establishing the amount of this reduction is given, depending on the size of the solute molecule and the effective pore radius of the membrane. With the help of these results, a hypothetical biological membrane moving water by osmotic and hydrostatic pressure gradients is discussed.

Design methodology of a highly loaded tandem rotor and its performance analysis under clean and distorted inflows

2021 ◽  
pp. 095440622110160
Author(s):  
Amit Kumar ◽  
AM Pradeep
Keyword(s):  
Experimental Analysis ◽  
Total Pressure ◽  
Pressure Rise ◽  
Pressure Gradients ◽  
Complex Flow ◽  
Angle Variation ◽  
Stall Margin ◽  
Rotor Design ◽  
Flow Through ◽  
Aerodynamic Parameters

Compact and efficient compressor design is one of the key challenges in aero-engine development. The flow through a compressor is exposed to adverse pressure gradients, which limits the maximum allowable flow turning in a compressor blade. Tandem blading is an interesting concept to achieve a higher total pressure rise by augmenting the flow turning angle. Variation in axial overlap and percentage pitch of the forward and aft blade elements largely influences the behavior of the tandem configuration. In the present study, the genetic algorithm is used to optimize the axial overlap and the percentage pitch for the tandem rotor. Results indicate that a lower axial overlap and higher percentage pitch results in optimum performance. The paper presents the parametric study of four tandem configurations with different axial overlaps and percentage pitches. A detailed experimental analysis of the four different tandem configurations is included in this paper. The behavior of the tandem rotor is examined under the clean and radially distorted inflow. Further, a comparison is drawn with a conventional single rotor in terms of aerodynamic parameters such as total pressure rise, axial velocity, and stall margin. The experimental analysis is supplemented by some interesting computational results, which are included to provide some insight into the complex flow field of the tandem rotor. Tandem rotor design is observed to have a higher sensitivity to radial tip inflow distortion. The upstream shift of the aft rotor blade adversely affects the total pressure rise and stall margin of the tandem rotor.

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