The Effect of Mach Number and Aspect Ratio on the Interfacial Characteristics of a Submerged Rectangular Gas Jet

2010 ◽  
Author(s):  
Chris Weiland ◽  
Pavlos Vlachos
Keyword(s):  
Mach Number ◽  
Aspect Ratio ◽  
Gas Jet ◽  
Non Invasive ◽  
Gas Jets ◽  
Aspect Ratios ◽  
Instability Growth ◽  
Logarithmic Decay ◽  
The Stability ◽  
Geometric Length

Gas jets formed by rectangular nozzles submerged in water were studied using a non-invasive photographic technique which allowed simultaneous measurements of the entire interface. Three aspect ratios were considered corresponding to 2, 10, and 20 with all nozzles sharing a common width. As far as the authors know this study represents the first time the effects of aspect ratio and Mach number on a submerged gas jet have been studied. The results indicate aspect ratio and Mach number play a large role in dictating both the unsteadiness of the interface and the penetration of the gas jet into the surrounding liquid medium. The jet pinch-off is shown to have a logarithmic decay with increasing Mach number and when appropriately scaled by the total viewing length and a geometric length scale (LQ) is relatively constant across all aspect ratio nozzles. The location of pinch-off is also a function of aspect ratio, with the subsonic aspect ratio 2 nozzles showing maximum pinch-off at y/LQ ≈ 23–26 while sonic and supersonic Mach numbers have peaks over the range y/LQ ≈ 11–14. The AR 10 and 20 nozzles show no dependence on Mach number with the maximum number of pinch-off events observed over the interval y/LQ ≈ 3–5. Jet spreading which is indicative of liquid entrainment is also shown to increase with Mach number and aspect ratio. The jet penetration also increases with increasing Mach number and aspect ratio. The spatial instability growth rate was deduced from the downstream evolution of the interfacial unsteadiness and it is shown that the nozzle with aspect ratio of 2 follows a different trend than the aspect ratio 10 and 20 nozzles, suggesting a fundamentally different mechanism dominates the stability of large aspect ratio rectangular gas jets.

FIV Characteristics of U-Tubes Due to Relocation of the Tube Support Plate

2005 ◽  
Author(s):  
Ki-Wahn Ryu ◽  
Hyung-Jin Kim ◽  
Chi-Yong Park
Keyword(s):  
Aspect Ratio ◽  
Steam Generator ◽  
Mode Shapes ◽  
Design Stage ◽  
Parameter Study ◽  
Stability Ratio ◽  
Integrity Assessment ◽  
Support Plate ◽  
Aspect Ratios ◽  
The Stability

Fluid-elastic instability and turbulence excitation for an under developing steam generator are investigated numerically. The stability ratio and the amplitude of turbulence excitation are obtained by using the PIAT (Program for Integrity Assessment of Steam Generator Tube) code from the information on the thermal-hydraulic data of the steam generator. The aspect ratio, the ratio between the height of U-tube from the upper most tube support plate (h) and the width of two vertical portion of U-tube (w), is defined for geometric parameter study. Several aspect ratios with relocation of tube support plates are adopted to study the effects on the mode shapes and characteristics of flow-induced vibration. When the aspect ratio exceeds value of 1, most of the mode shapes at low frequency are generated at the top of U-tube. It makes very high value of the stability ratio and the amplitude of turbulent excitation as well. We can consider that the local mode shape at the upper side of U-tube will develop the wear phenomena between the tube and the anti-vibration bars such as vertical, horizontal, and diagonal strips. It turns out that the aspect ratio reveals very important parameter for the design stage of the steam generator. The appropriate value of the aspect ratio should be specified and applied.

Straight Channel Diffuser Performance at High Inlet Mach Numbers

1969 ◽  
Vol 91 (3) ◽  
pp. 397-412 ◽  
Author(s):  
P. W. Runstadler ◽  
R. C. Dean
Keyword(s):  
Mach Number ◽  
Aspect Ratio ◽  
Pressure Recovery ◽  
Straight Channel ◽  
Single Plane ◽  
Aspect Ratios ◽  
Straight Wall ◽  
Throat Width ◽  
Mach Numbers

Measurements have been made of the pressure recovery of straight wall, single plane divergence diffusers with inlet Mach numbers between 0.2 and choking (0.2 ≤ Mt < 1.0). In contrast to the widely held assertion in the literature, there is no “critical” inlet subsonic Mach number above which pressure recovery decreases drastically. Two aspect ratios, AS = 0.25 and 1.0, have been studied for a range of length-to-throat-width ratios L/W1 and divergence angles 2θ around the regions of peak recovery. Diffuser performance maps are given showing pressure recovery Cp as a function of diffuser geometry for fixed values of throat Mach number Mt, throat blockage B, and aspect ratio AS. Significant changes in the location and magnitude of pressure recovery do occur with variations in Mt, B, and AS. The importance to the designer of a knowledge of how diffuser performance depends upon geometric and diffuser inlet parameters is discussed.

Experimental Study of the Stability of a High-Speed Gas Jet Under the Influence of Liquid Cross-Flow

2007 ◽  
Author(s):  
Chris Weiland ◽  
Jon Yagla ◽  
Pavlos Vlachos
Keyword(s):  
Mach Number ◽  
Free Boundary ◽  
Boundary Conditions ◽  
High Speed ◽  
Cross Flow ◽  
Upper And Lower Bounds ◽  
Gas Jet ◽  
Mode Shapes ◽  
Free Boundary Conditions ◽  
The Stability

This paper reports on the interfacial character and deflection of a high-speed gas jet transverse to an aqueous cross-flow as a function of cross-flow speed and gas jet Mach number. Several gas exit velocities were tested including subsonic cases up to supersonic cases at cross-flow velocities from 0.3 m/s to 0.7 m/s. For the subsonic cases, it was found that the stability and resistance of the gas jet to deflect in the presence of cross-flow were increased with the jet Mach number. However, the Mach 1.6 jet was more stable than the Mach 1.9 jet, suggesting that there exists upper and lower bounds for jet stability which are Mach number dependent. Unstable gas jets were shown to pinch-off, meaning the interface of the gas jet in a plane parallel to the ejector exit collapsed to almost a point and an independent bubble rose to the free surface. The stagnation side gas/liquid interfaces were analyzed using the Proper Orthogonal Decomposition (POD) method to better understand the fundamental mode shapes contained in the interface waveforms. It was found that the subsonic jets shared many of the same characteristics in their first, second, and third mode shapes. The supersonic jets differed from the subsonic mode shapes. Interestingly, the mode shapes for the subsonic cases compared well to those of a beam in transverse vibration with sliding-free boundary conditions. The supersonic cases compared relatively well to pinned-free boundary conditions, owing to the more columnar nature of the gas jet as it exited the ejector.

Low Aspect Ratio Turbines

1964 ◽  
Vol 86 (1) ◽  
pp. 13-16 ◽  
Author(s):  
Gunnar O. Ohlsson
Keyword(s):  
Reynolds Number ◽  
Mach Number ◽  
Aspect Ratio ◽  
Axial Distance ◽  
Mass Rate ◽  
Low Aspect Ratio ◽  
Turbine Efficiency ◽  
Aspect Ratios

Four different axial, impulse turbines with extremely low aspect ratios (between 0.07 and 0.70) were tested over wide ranges of pressure and speed ratios. The influence on mass rate of flow and efficiency of Reynolds number and axial distance between stator and rotor is given. Stator and rotor efficiency, Mach number, and flow angles, as well as other quantities, are obtained by means of a wheel with axial outlet. Semiempirical formulas are given for turbine efficiency, stator efficiency, and rotor efficiency as functions of aspect ratio.

The Plate Buckling Coefficient

1967 ◽  
Vol 71 (673) ◽  
pp. 37-40 ◽  
Author(s):  
P. S. Bulson
Keyword(s):  
Aspect Ratio ◽  
Close Approximation ◽  
Families Of Curves ◽  
Aspect Ratios ◽  
Plate Buckling ◽  
Plate Aspect Ratio ◽  
Exact Shape ◽  
Buckling Coefficient ◽  
Thin Walled ◽  
The Stability

SummaryThe stability of a compressed plate is examined, using the energy method, with transverse deflections defined by a function giving the exact shape, but never specified. By this means it is possible to make observations about the form of the plate buckling coefficient. This form is examined tor two cases of loading, and it is demonstrated that a close approximation to the complete curve linking the buckling coefficient with plate aspect ratio can be deduced. The method is applicable to single plates or thin walled members consisting of an assembly of plates, and enables families of curves connecting buckling coefficients with aspect ratios to be summarised in a single relationship.

Experimental Investigation on the Motion of Particle Cloud in Viscous Fluids

2018 ◽  
Vol 141 (3) ◽  
Author(s):  
Amir H. Azimi
Keyword(s):  
Aspect Ratio ◽  
Drag Coefficient ◽  
Viscous Fluids ◽  
Air Bubbles ◽  
Aspect Ratios ◽  
Particle Clouds ◽  
Flow Through ◽  
Using Data ◽  
The Stability ◽  
Individual Particles

Laboratory experiments were conducted to study the dynamics of particle clouds in viscous fluids. Different shapes of frontal head and trailing stems were observed, and particle clouds were classified using data mining methodology. The stability of the frontal head of particle clouds was found to be correlated with the nozzle diameter and mass of sand particles in the form of an initial aspect ratio. The formation of particle clusters into a torus and the split of the frontal head into two or three clusters were investigated in detail. The cluster of particles flow through viscous fluid experienced partial separation due to the release of air bubbles from the rear of frontal head. It was observed that the time and location of major particle separation increase linearly with the aspect ratio. The oscillatory motion of the frontal head, caused by an uneven release of air bubbles from the rear of the frontal head, was found to be correlated with the initial aspect ratio. Both amplitude and wavelength exhibited a linear relationship with nondimensional time. The average drag coefficient of particle clouds Cd in viscous fluids was calculated for different aspect ratios, and the results were compared with the drag coefficient of individual particles. It was found that the averaged drag coefficients of particle clouds were smaller than the drag coefficient of individual particles, and Cd slightly increases with the increasing initial aspect ratio.

Pressure fluctuations due to ‘trapped waves’ in the initial region of compressible jets

2021 ◽  
Vol 931 ◽  
Author(s):  
K.B.M.Q. Zaman ◽  
A.F. Fagan ◽  
P. Upadhyay
Keyword(s):  
Mach Number ◽  
Aspect Ratio ◽  
Pressure Fluctuations ◽  
Major Axis ◽  
Trapped Waves ◽  
Potential Core ◽  
Screech Tone ◽  
Aspect Ratios ◽  
Supersonic Regime ◽  
Different Diameters

An experimental study is conducted on unsteady pressure fluctuations occurring near the nozzle exit and just outside the shear layer of compressible jets. These fluctuations are related to ‘trapped waves’ within the jet's potential core, as investigated and reported recently by other researchers. Round nozzles of three different diameters and rectangular nozzles of various aspect ratios are studied. The fluctuations manifest as a series of peaks in the spectra of the fluctuating pressure. Usually the first peak at the lowest frequency (fundamental) has the highest amplitude and the amplitude decreases progressively for successive peaks at higher frequencies. These ‘trapped wave spectral peaks’ are found to occur with all jets at high subsonic conditions and persist into the supersonic regime. Their characteristics and variations with axial and radial distances, jet Mach number and aspect ratio of the nozzle are documented. For round nozzles, the frequency of the fundamental is found to be independent of the jet's exit boundary layer characteristics and scales with the nozzle diameter. On a Strouhal number (based on diameter) versus jet Mach number plot it is represented by a unique curve. Relative to the fundamental the frequencies of the successive peaks are found to bear the ratios of 5/3, 7/3, 9/3 and so on, at a given Mach number. For rectangular nozzles, the number of peaks observed on the major axis is found to be greater than that observed on the minor axis by a factor approximately equal to the nozzle's aspect ratio; the fundamental is the same on either edge. For all nozzles the onset of screech tones appears as a continuation of the evolution of these peaks; it is as if one of these peaks abruptly increases in amplitude and turns into a screech tone as the jet Mach number is increased.

scholarly journals Wind Tunnel Testing on Start/Unstart Characteristics of Finite Supersonic Biplane Wing

2013 ◽  
Vol 2013 ◽  
pp. 1-10 ◽  
Author(s):  
Hiroshi Yamashita ◽  
Naoshi Kuratani ◽  
Masahito Yonezawa ◽  
Toshihiro Ogawa ◽  
Hiroki Nagai ◽  
...  
Keyword(s):  
Mach Number ◽  
Aspect Ratio ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Wind Tunnels ◽  
Wind Tunnel Testing ◽  
Ratio Model ◽  
Number Range ◽  
Aspect Ratios ◽  
Schlieren System

This study describes the start/unstart characteristics of a finite and rectangular supersonic biplane wing. Two wing models were tested in wind tunnels with aspect ratios of 0.75 (model A) and 2.5 (model B). The models were composed of a Busemann biplane section. The tests were carried out using supersonic and transonic wind tunnels over a Mach number range of0.3≤M∞≤2.3with angles of attack of 0°, 2°, and 4°. The Schlieren system was used to observe the flow characteristics around the models. The experimental results showed that these models had start/unstart characteristics that differed from those of the Busemann biplane (two dimensional) owing to three-dimensional effects. Models A and B started at lower Mach numbers than the Busemann biplane. The characteristics also varied with aspect ratio: model A (1.3<M∞<1.5) started at a lower Mach number than model B (1.6<M∞<1.8) owing to the lower aspect ratio. Model B was located in the double solution domain for the start/unstart characteristics atM∞=1.7, and model B was in either the start or unstart state atM∞=1.7. Once the state was determined, either state was stable.

The role of advance ratio and aspect ratio in determining leading-edge vortex stability for flapping flight

2014 ◽  
Vol 751 ◽  
pp. 71-105 ◽  
Author(s):  
R. R. Harbig ◽  
J. Sheridan ◽  
M. C. Thompson
Keyword(s):  
Aspect Ratio ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Leading Edge Vortex ◽  
Aspect Ratios ◽  
Edge Vortex ◽  
Advance Ratio ◽  
Vorticity Production ◽  
The Stability

AbstractThe effects of advance ratio and the wing’s aspect ratio on the structure of the leading-edge vortex (LEV) that forms on flapping and rotating wings under insect-like flight conditions are not well understood. However, recent studies have indicated that they could play a role in determining the stable attachment of the LEV. In this study, a numerical model of a flapping wing at insect Reynolds numbers is used to explore the effects of these parameters on the characteristics and stability of the LEV. The word ‘stability’ is used here to describe whether the LEV was attached throughout the stroke or if it was shed. It is demonstrated that increasing the advance ratio enhances vorticity production at the leading edge during the downstroke, and this results in more rapid growth of the LEV for non-zero advance ratios. Increasing the wing aspect ratio was found to have the effect of shortening the wing’s chord length relative to the LEV’s size. These two effects combined determine the stability of the LEV. For high advance ratios and large aspect ratios, the LEV was observed to quickly grow to envelop the entire wing during the early stages of the downstroke. Continued rotation of the wing resulted in the LEV being eventually shed as part of a vortex loop that peels away from the wing’s tip. The shedding of the LEV for high-aspect-ratio wings at non-zero advance ratios leads to reduced aerodynamic performance of these wings, which helps to explain why a number of insect species have evolved to have low-aspect-ratio wings.

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