scholarly journals Air–Water Bubbly Flow by Multiple Vents on a Hydrofoil in a Steady Free-Stream

2021 ◽  
Vol 11 (21) ◽  
pp. 9890
Author(s):  
Kiseong Kim ◽  
David Nagarathinam ◽  
Byoung-Kwon Ahn ◽  
Cheolsoo Park ◽  
Gun-Do Kim ◽  
...  
Keyword(s):  
Regression Analysis ◽  
Power Law ◽  
High Speed ◽  
Free Stream ◽  
Bubbly Flow ◽  
Air Injection ◽  
Spatial Density ◽  
Side View ◽  
Dimensional Flow ◽  
Flow Features

Flow features, due to air injection through multiple vents on the surface of a hydrofoil inclined at an angle with respect to the free-stream in a cavitation tunnel, are presented here. The hydrofoil, with a chord length, c, is oriented at the angle of inclination, α=3.5∘. The Froude number, Fn, based on the free-stream velocity, V∞, and air injection vent diameter, dh, is 30.30,50.51 and 70.71. Air is injected through multiple vents on the hydrofoil at the non-dimensional air injection coefficient, Cq∼16−8917. The air bubble packing per unit area is quantified using spatial density, SD, at various combinations of Fn,Cq based on a high-speed video from the side view. The time-averaged spatial density, <SD>, is observed to increase in a logarithmic manner with an increase in the air injection rate, Q, at various Froude numbers. There is an increase in the mean spatial density of the bubbles with the increase in Cq at all Fn. A power–law relation is shown to exist between the time-averaged spatial density, <SD>, and the non-dimensional flow variables, Reynolds number, Reair, Fn and Cq based on a regression analysis. By tracking individual finite volume bubbles flowing with the free-stream, the bubble dimensions in pixels are quantified using quantities such as the deformation rate, ϵ, and standardization, ϵS, from the side-view videos. It is observed that ϵ and ϵS change with time, even as they become advected with the free-stream. Through high-speed imaging from the top view, we characterize the bubbly flow features’ time-averaged thickness, t, at various combinations of Fn,Cq at α=3.5∘. We obtain a power-law relation between the non-dimensional time-averaged jet thickness, t/c, and the non-dimensional flow parameters such as, Reair, Fn,Cq and the non-dimensional streamwise distance, x/xref, based on a regression analysis, where xref is a reference distance. The results are relevant to engineering applications where the air–water bubbly flow in a free-stream is important.

Unstart phenomena induced by mass addition and heat release in a model scramjet

2016 ◽  
Vol 797 ◽  
pp. 604-629 ◽  
Author(s):  
S. Im ◽  
D. Baccarella ◽  
B. McGann ◽  
Q. Liu ◽  
L. Wermer ◽  
...  
Keyword(s):  
Heat Release ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
High Speed ◽  
Free Stream ◽  
Mass Loading ◽  
High Enthalpy ◽  
Hypersonic Wind Tunnel ◽  
Flow Features

The unstart phenomena in a model scramjet with a free stream Mach number of 4.5 were investigated at an arc-heated hypersonic wind tunnel. High-speed schlieren imaging and high resonance frequency pressure measurements were used to capture the flow features during the unstart process. Three unstart conditions were tested: (i) a low-enthalpy free stream with mass loading, (ii) a high-enthalpy free stream with mass loading and (iii) a high-enthalpy free stream with mass loading and heat release. It was revealed that the unstart threshold and the time from the onset to the completion of unstart depended strongly on the mass loading rate and the heat exchange. The negative heat addition (cooling) significantly increased the threshold of mass flow rate triggering unstart. The decrement of the mass flow rate threshold for unstart was observed in the presence of heat release by combustion. The observed transient and quasi-steady behaviours of the unstart shockwave system and the jet motion were similar in all of the test conditions. On the other hand, at the lip of inlet model, the unstart shockwave under the cold free stream condition exhibited a relatively steady behaviour while severe oscillatory flow motions of the jet and the unstart shockwave were observed in the combustion-driven unstart process. The different unstarted flow behaviours between the three flow conditions were explained using a simplified one-dimensional flow choking analysis and use of the Korkegi criterion.

Aspects of Shear Layer Unsteadiness in a Three-Dimensional Supersonic Wake

2005 ◽  
Vol 127 (6) ◽  
pp. 1085-1094 ◽  
Author(s):  
Alan L. Kastengren ◽  
J. Craig Dutton
Keyword(s):  
Shear Layer ◽  
Stream Flow ◽  
Free Stream ◽  
Angle Of Attack ◽  
Three Dimensional ◽  
Base Flow ◽  
Recirculation Region ◽  
Side View ◽  
Near Wake ◽  
Supersonic Wake

The near wake of a blunt-base cylinder at 10° angle-of-attack to a Mach 2.46 free-stream flow is visualized at several locations to study unsteady aspects of its structure. In both side-view and end-view images, the shear layer flapping grows monotonically as the shear layer develops, similar to the trends seen in a corresponding axisymmetric supersonic base flow. The interface convolution, a measure of the tortuousness of the shear layer, peaks for side-view and end-view images during recompression. The high convolution for a septum of fluid seen in the middle of the wake indicates that the septum actively entrains fluid from the recirculation region, which helps to explain the low base pressure for this wake compared to that for a corresponding axisymmetric wake.

Bubble Breakup Phenomena in a Venturi Tube

2007 ◽  
Author(s):  
A. Fujiwara ◽  
K. Okamoto ◽  
K. Hashiguchi ◽  
J. Peixinho ◽  
S. Takagi ◽  
...  
Keyword(s):  
High Speed ◽  
Bubbly Flow ◽  
Bubble Diameter ◽  
Pressure Change ◽  
Venturi Tube ◽  
Large Bubble ◽  
Breakup Process ◽  
Bubble Behavior ◽  
Bubble Breakup ◽  
Unstable Surface

Microbubble generation techniques have been proposed in former investigations. Here, we study an effective technique using air bubbly flow into a convergent-divergent nozzle (venturi tube). Pressure change in the diverging section induces bubble breakup. The purpose of this study is to clarify the effect of flow velocity at the throat with respect to the bubble breakup process and the bubble behavior in a venturi tube. Relations between generated bubble diameter and bubble breakup process are also described. Using high speed camera for detailed observation of bubble behavior, the following features were obtained. The velocity at the throat is expected to be of the order of the magnitude of the speed of sound of bubbly flow and a drastic bubble expansion and a shrink is induced. Besides, a liquid column appeared after the bubble flowing into the throat, and it grew up to stick to the bubble like in the form of a jet. This jet induced both unstable surface waves and the breakup of a single large bubble into several pieces.

Effect of Air Fraction on Force Coefficients in Oscillatory Flow

2021 ◽  
Author(s):  
Malene Hovgaard Vested ◽  
Erik Damgaard Christensen
Keyword(s):  
High Speed ◽  
Offshore Structures ◽  
Air Injection ◽  
Wave Loads ◽  
Morison Equation ◽  
Force Coefficients ◽  
Air Content ◽  
Set Up ◽  
High Level ◽  
Spilling Breakers

Abstract The forces on marine and offshore structures are often affected by spilling breakers. The spilling breaker is characterized by a roller of mixed air and water with a forward speed approximately equal to the wave celerity. This high speed in the top of the wave has the potential to induce high wave loads on upper parts of the structures. This study analyzed the effect of the air content on the forces. The analyses used the Morison equation to examine the effect of the percentage of air on the forces. An experimental set-up was developed to include the injection of air into an otherwise calm water body. The air-injection did introduce a high level a turbulence. It was possible to assess the amount of air content in the water for different amounts of air-injection. In the mixture of air and water the force on an oscillating square cylinder was measured for different levels of air-content, — also in the case without air. The measurements indicated that force coefficients for clear water could be use in the Morison equation as long as the density for water was replaced by the density for the mixture of air and water.

Stability Enhancement of Supercavitating Projectiles by Unsteady Air Injection

2005 ◽  
Author(s):  
Yasmin Khakpour ◽  
Miad Yazdani
Keyword(s):  
Numerical Simulation ◽  
Drag Reduction ◽  
High Speed ◽  
The Body ◽  
Air Injection ◽  
Cavity Surface ◽  
The Stability ◽  
Stability Enhancement

In this work, numerical simulation is used to study the stability enhancement of high speed supercavitating hydrofoils. Although supercavitation is known as one of the most effective methods for drag reduction, producing the cavity, either by ventilation or by cavitator at front of the body, may cause some instabilities on cavity surface and thus on the projectile’s motion. Therefore removing these instabilities comes as an important point of discussion. First of all, we calculate the sources of instabilities and measure respective forces and then present some approaches that significantly reduce these instabilities. One of these methods that could produce more stable supercavities is injecting of the air into the cavity unsteadily which varies through the projectile’s surface. This approach is provided by arrays of slots distributed on the projectile’s surface and unsteady injection is modeled over the surface. Furthermore, the position of ventilation, dramatically affects the stability like those in aerodynamics. In all approaches it is assumed that the supercavity covers the whole of the body, however the forces caused by the wakes, formed behind the body are taken into account. The calculation is performed at three cavitation numbers with respective velocities of 40 m/s, 50 m/s, 60 m/s.

A Theory for the High-Speed Flow of Gas-Solids Mixtures under Conditions of Equilibrium and Constant Fractional Lag

1969 ◽  
Vol 184 (3) ◽  
pp. 59-66 ◽  
Author(s):  
B. N. Cole ◽  
H. M. Bowers ◽  
F. R. Mobbs
Keyword(s):  
Mach Number ◽  
Speed Of Sound ◽  
Gas Dynamics ◽  
High Speed ◽  
Solid Particles ◽  
High Speed Flow ◽  
One Dimensional ◽  
Dimensional Flow ◽  
Speed Flow ◽  
Constant Area

A theory is presented for the high-speed, one-dimensional flow of a gas-solids mixture, assuming constant fractional lags of temperature and velocity between the solid particles and the gas. A mixture speed of sound is is derived and used as the basis of a mixture Mach number. Expressions are deduced which are parallel to many well-known relationships in orthodox one-dimensional gas dynamics. The investigation covers frictionless flow in a variable area duct and flow with friction in a constant area duct. The effect of solids volume is also taken into account.

Improvement of Estimation of Objective Scores of Answer Statements Posted at Q&A Sites

2013 ◽  
Vol 1 (4) ◽  
pp. 16-30
Author(s):  
Yuya Yokoyama ◽  
Teruhisa Hochin ◽  
Hiroki Nomiya
Keyword(s):  
Regression Analysis ◽  
Multiple Regression ◽  
Power Law ◽  
Estimation Accuracy ◽  
Factor Scores ◽  
Human Relationships ◽  
Explanatory Variables ◽  
Natural Logarithm ◽  
Question And Answer ◽  
Feature Values

To eliminate mismatches between the intentions of questioners and respondents of Question and Answer (Q&A) sites, the authors have clarified the characteristics of the question and answer statements. It has been shown that the impression of the statements could be captured by nine factors, and the factor scores could be estimated from the feature values of the statements. Here, the objective scores of answer statements are provided. So far the authors have tried to estimate the objective scores of answer statements through multiple regression analysis. They are estimated from the factor scores estimated by using multiple regression formulas already obtained. As a result, with the consideration of natural logarithm, objective scores of the statements on love counseling & human relationships could be estimated good. The estimation accuracy of the statements on Yahoo! Auction and PC, however, is required to be improved. Therefore, this paper tries to improve the estimation accuracy of objective scores of Yahoo! Auction and PC. Here, the authors adopt Steven's power law as well as Fechner's law as new explanatory variables. In considering multicollinearity, the authors selected as many explanatory variables as possible. As a result, objective scores of the statements of PC are estimated fairly good.

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