Co-rotating equal strength vortex pair merging in pressure gradient environment

2016 ◽  
Author(s):  
Yuan Yi ◽  
Peiqing Liu ◽  
Tianxiang Hu
Keyword(s):  
Pressure Gradient ◽  
Vortex Pair ◽  
Equal Strength ◽  
Gradient Environment

Three-Dimensional Velocity Measurements of Film Cooling Flow Under Favorable Pressure Gradient

2012 ◽  
Author(s):  
Filippo Coletti ◽  
Christopher J. Elkins ◽  
John K. Eaton
Keyword(s):  
Pressure Gradient ◽  
Film Cooling ◽  
Flow Direction ◽  
Three Dimensional ◽  
Vortex Pair ◽  
Strong Impact ◽  
Cooling Flow ◽  
Magnetic Resonance Velocimetry ◽  
Favorable Pressure Gradient ◽  
Streamwise Pressure Gradient

This paper addresses the effect of a favorable streamwise pressure gradient on the velocity field of a single-hole film cooling configuration, operating at unity blowing ratio. The hole is circular and inclined at 30 degrees with respect to the main flow direction. Magnetic Resonance Velocimetry is used to obtain the full three-dimensional field for a baseline configuration with negligible streamwise pressure gradient and for a configuration with favorable streamwise pressure gradient. In the latter case the acceleration parameter is K = 4.8·10−6, which is representative of the conditions along the pressure side of a turbine airfoil. The experiments are performed in water. The velocity and vorticity distributions highlight the strong impact of the favorable pressure gradient on the development of the counter-rotating vortex pair which dominates the dynamics of the film cooling flow. The accelerating flow drives the vortex pair towards the wall, while the increased stretching of the vortices augments their circulation. Both effects contribute to bring the counter-rotating vortices closer to each other. They also persist much further in space with respect to the zero-pressure-gradient case. Implications for the film cooling performance are discussed.

Building Block Experiments in Discrete Hole Film Cooling

2015 ◽  
Author(s):  
Kevin J. Ryan ◽  
Filippo Coletti ◽  
Christopher J. Elkins ◽  
John K. Eaton
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Building Block ◽  
Film Cooling ◽  
Three Dimensional ◽  
Vortex Pair ◽  
Mean Velocity ◽  
Jet Trajectory ◽  
Dominant Feature ◽  
Cooling Hole

This paper reports a series of building block experiments for discrete hole film cooling. Seven different configurations, including variations in injection wall curvature, mainstream pressure gradient, and boundary layer thickness are measured for a round film cooling hole, inclined 30 degrees at injection, and operated at a blowing ratio of unity. Full three dimensional, three component velocity fields and scalar coolant concentration fields are acquired using Magnetic Resonance Imaging (MRI) techniques. The results show the effect of varying the mainstream condition on the mean coolant concentration distribution and mean velocity field, including the counter-rotating vortex pair (CVP), a dominant feature of jet in crossflow type flows. The present study focuses on an analysis of the building block configurations only possible with full three dimensional velocity and concentration fields. Several scalar parameters including normalized perimeter, jet trajectory, maximum coolant concentration, and coolant concentration spread are extracted from the collected data and compared across the different configurations. The results indicate that the pressure gradient variations have the strongest effect on the calculated quantities, the boundary layer slightly less, and the curvature very little.

Activated Prominences; Mechanisms for Activation and Eruption

1979 ◽  
Vol 44 ◽  
pp. 307-313
Author(s):  
D.S. Spicer
Keyword(s):  
Pressure Gradient ◽  
Density Gradient ◽  
Current Density ◽  
Convective Instability ◽  
Tearing Mode ◽  
Magnetic Shear ◽  
Long Wavelength ◽  
Ideal Mhd ◽  
Gradient Change ◽  
Accelerated Particles

A possible relationship between the hot prominence transition sheath, increased internal turbulent and/or helical motion prior to prominence eruption and the prominence eruption (“disparition brusque”) is discussed. The associated darkening of the filament or brightening of the prominence is interpreted as a change in the prominence’s internal pressure gradient which, if of the correct sign, can lead to short wavelength turbulent convection within the prominence. Associated with such a pressure gradient change may be the alteration of the current density gradient within the prominence. Such a change in the current density gradient may also be due to the relative motion of the neighbouring plages thereby increasing the magnetic shear within the prominence, i.e., steepening the current density gradient. Depending on the magnitude of the current density gradient, i.e., magnetic shear, disruption of the prominence can occur by either a long wavelength ideal MHD helical (“kink”) convective instability and/or a long wavelength resistive helical (“kink”) convective instability (tearing mode). The long wavelength ideal MHD helical instability will lead to helical rotation and thus unwinding due to diamagnetic effects and plasma ejections due to convection. The long wavelength resistive helical instability will lead to both unwinding and plasma ejections, but also to accelerated plasma flow, long wavelength magnetic field filamentation, accelerated particles and long wavelength heating internal to the prominence.

An Attack on the Contamination Problem in the Electron Microscope

1967 ◽  
Vol 25 ◽  
pp. 368-368
Author(s):  
J. J. Kelsch ◽  
A. Holtz
Keyword(s):  
Electron Microscope ◽  
Pressure Gradient ◽  
Ionization Potential ◽  
Simple Solution ◽  
Specimen Surface ◽  
Contamination Rate ◽  
Local Pressure ◽  
High Ionization ◽  
Hydrocarbon Molecules ◽  
Contamination Problem

A simple solution to the serious problem of specimen contamination in the electron microscope is presented. This is accomplished by the introduction of clean helium into the vacuum exactly at the specimen position. The local pressure gradient thus established inhibits the migration of hydrocarbon molecules to the specimen surface. The high ionization potential of He permits the use of relatively large volumes of the gas, without interfering with gun stability. The contamination rate is reduced on metal samples by a factor of 10.

Hydration Chamber for Jeolco 200 Kv Microscope

1970 ◽  
Vol 28 ◽  
pp. 542-543
Author(s):  
V. R. Matricardi ◽  
G. G. Hausner ◽  
D. F. Parsons
Keyword(s):  
Electron Microscope ◽  
Water Vapor ◽  
Vapor Pressure ◽  
Pressure Gradient ◽  
Room Temperature ◽  
List Type ◽  
Type Number ◽  
Equilibrium Vapor Pressure

In order to observe room temperature hydrated specimens in an electron microscope, the following conditions should be satisfied: The specimen should be surrounded by water vapor as close as possible to the equilibrium vapor pressure corresponding to the temperature of the specimen.The specimen grid should be inserted, focused and photo graphed in the shortest possible time in order to minimize dehydration.The full area of the specimen grid should be visible in order to minimize the number of changes of specimen required.There should be no pressure gradient across the grid so that specimens can be straddled across holes.Leakage of water vapor to the column should be minimized.

Risk Factors for Hepatic Encephalopathy after Transjugular Intrahepatic Portosystemic Shunt in Patients with Hepatocellular Carcinoma and Portal Hypertension

2015 ◽  
Vol 24 (3) ◽  
pp. 301-307 ◽  
Author(s):  
Jiannan Yao ◽  
Li Zuo ◽  
Guangyu An ◽  
Zhendong Yue ◽  
Hongwei Zhao ◽  
...  
Keyword(s):  
Risk Factors ◽  
Hepatocellular Carcinoma ◽  
Portal Hypertension ◽  
Hepatic Encephalopathy ◽  
Pressure Gradient ◽  
Transjugular Intrahepatic Portosystemic Shunt ◽  
Meld Score ◽  
Portosystemic Shunt ◽  
Portal Flow ◽  
Intrahepatic Portosystemic Shunt

Aims: This study aimed at assessing the risk factors for hepatic encephalopathy (HE) after transjugular intrahepatic portosystemic shunt (TIPS) in patients with hepatocellular carcinoma (HCC) and portal hypertension. Method: Consecutive patients (n=279) with primary HCC who underwent TIPS between January 1997 and March 2012 at a single institution were retrospectively reviewed. Patients were followed up for 2 years. Pre-TIPS, peri-TIPS and post-TIPS clinical variables were reviewed using univariate and multivariate analyses to identify risk factors for HE after TIPS. Results: The overall incidence of HE was 41% (114/279). Multivariate analysis showed an increased odds for HE in patients with: >3 treatments with transcatheter arterial chemoembolization (TACE) and/or trans-arterial embolization (TAE) (odds ratio [OR], 4.078; 95% confidence interval [95%CI], 1.748-9.515); hepatopetal portal flow (OR, 2.362; 95%CI, 1.032-5.404); high portosystemic pressure gradient (OR, 1.198; 95%CI, 1.073-1.336) and high pre-TIPS MELD score (OR, 1.693; 95%CI, 1.390-2.062). Odds for HE were increased 1.693 fold for each 1-point increase in the MELD score, and 1.198 fold for each 1-mmHg decrease in the post-TIPS portosystemic pressure gradient. Conclusion: The identification of clinical variables associated with increased odds of HE may be useful for the selection of appropriate candidates for TIPS. Results suggest that an inappropriate decrease in the portosystemic pressure gradient might be associated with HE after TIPS. In addition, >3 treatments with TACE/TAE, hepatopetal portal flow, and high MELD score were also associated with increased odds of HE after TIPS. Key words:  –  –  – .

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