Experimental Study of Near-Field Entrainment of Moderately Overpressured Jets

2011 ◽  
Vol 133 (5) ◽  
Author(s):  
Stephen A. Solovitz ◽  
Larry G. Mastin ◽  
Farhad Saffaraval
Keyword(s):  
High Speed ◽  
Near Field ◽  
Flow Region ◽  
Flow Conditions ◽  
Entrainment Ratio ◽  
One Dimensional ◽  
Column Collapse ◽  
Developing Flow ◽  
Image Velocimetry ◽  
Velocity Flow

Particle image velocimetry (PIV) experiments have been conducted to study the velocity flow fields in the developing flow region of high-speed jets. These velocity distributions were examined to determine the entrained mass flow over a range of geometric and flow conditions, including overpressured cases up to an overpressure ratio of 2.83. In the region near the jet exit, all measured flows exhibited the same entrainment up until the location of the first shock when overpressured. Beyond this location, the entrainment was reduced with increasing overpressure ratio, falling to approximately 60% of the magnitudes seen when subsonic. Since entrainment ratios based on lower speed, subsonic results are typically used in one-dimensional volcanological models of plume development, the current analytical methods will underestimate the likelihood of column collapse. In addition, the concept of the entrainment ratio normalization is examined in detail, as several key assumptions in this methodology do not apply when overpressured.

Velocity Measurements in Microchannels With a Laser Scanning Microscope and Particle Linear Image Velocimetry

2004 ◽  
Author(s):  
S. H. Chao ◽  
M. R. Holl ◽  
J. H. Koschwanez ◽  
R. H. Carlson ◽  
L. S. Jang ◽  
...  
Keyword(s):  
High Speed ◽  
Laser Scanning ◽  
Frame Rate ◽  
Planar Imaging ◽  
Velocity Measurements ◽  
Optical Sectioning ◽  
One Dimensional ◽  
Microscale Flow ◽  
Imaging Results ◽  
Image Velocimetry

A novel velocity measurement method for microscale flow field characterization is reported, particle linear image velocimetry (PLIV). The method records a series of one-dimensional images that represent the trace of particles in the flow across a one-dimensional imager. Linear imaging results in a faster frame rate than planar imaging, allowing observation of larger microscope magnification or measurement of faster flow rates in real-time than comparable techniques. In contrast to particle image velocimetry (PIV), PLIV does not require high-speed cameras or shutters. Furthermore, PLIV is adaptable to multiple linear imager formats and, as one example, can use laser scanning confocal microscopes (LSCM) that acquire images slowly but with high spatial resolutions and optical sectioning ability. Higher resolution can be obtained for flows where in-plane velocity gradient in the direction of the optical path (z-direction) is important. This paper presents the PLIV algorithm, and demonstrates its utility by measuring Poiseuille flow with 1-μm resolution in a microfluidic environment.

Measurement of the Acceleration Field of the High-Speed Jet Sound Producing Region

2007 ◽  
Author(s):  
Jeremy T. Pinier ◽  
Mark N. Glauser
Keyword(s):  
Flow Control ◽  
High Speed ◽  
Sound Production ◽  
Near Field ◽  
Pressure Sensors ◽  
Control Device ◽  
Synthetic Jets ◽  
Flow Control Device ◽  
Image Velocimetry ◽  
Derivatives Of

With the aim of being capable of controlling the sound created by high-speed jets or engine exhausts, a preliminary experiment, using a near-field azimuthal array of 15 pressure sensors and a far-field array of 6 microphones, pointed out the region of highest sound production in the turbulent flow where a dual-time particle image velocimetry (DT-PIV) investigation is now being carried out. This measurement technique enables access to time-derivatives of the velocity field which is a quantity of great interest for developing prediction capabilities crucial for closed-loop flow control. Jointly, a flow control device using synthetic jets is developed and PIV measurements are taken with and without the control to assess the effectiveness of such devices for aeroacoustic flow control.

Simulation and Experimental Investigation of Micro-Mixing Phenomena in the Microchannels

2009 ◽  
Author(s):  
Yun-Long Shao
Keyword(s):  
High Speed ◽  
Particle Image ◽  
Ccd Camera ◽  
Particle Image Velocimetry System ◽  
Flow Conditions ◽  
Micro Piv ◽  
Image Velocimetry ◽  
Micro Channels ◽  
Different Types ◽  
Better Than

The Lattice Boltzmann Equation (LBE) method is described for simulating micro-scale phenomena. In this paper, we have designed and manufactured several different types of micro-channels, and try to simulate the flows using the LBE method with PC cluster. Besides, In-house developed micro-PIV (Particle Image Velocimetry) system and high-speed CCD camera are then used to visualize the mixing and measure the velocity distribution within the channels at different flow conditions. Preliminary result shows that the micro-mixing induced by the meander-type channel is better than the other types of channel.

An Improved Preliminary Design Method for Ejectors

2003 ◽  
Author(s):  
Knox T. Millsaps ◽  
John C. Markowicz
Keyword(s):  
Momentum Flux ◽  
Design Method ◽  
Aerodynamic Performance ◽  
Preliminary Design ◽  
Flow Conditions ◽  
Shear Forces ◽  
Entrainment Ratio ◽  
Trade Off ◽  
One Dimensional ◽  
Cold Flow

A preliminary design method is presented for evaluating ejector geometries and predicting variations in aerodynamic performance due to changes in configurations and flow conditions. The method is based on steady, quasi-one dimensional conservation equations for mass, momentum, and energy with corrections to account for losses due to the primary nozzle exit, inlet to the mixing tube, frictional shear forces on the mixing tube walls, and outlet non-uniformity in the velocity profile from the mixing tube. The entrainment ratio, which is defined as the induced secondary flow (cold) rate divided by the primary (hot) flow rate, is first compared to ideal performance, which is obtained without losses. Next the results of the model are compared to experimental data, obtained from several ejector configurations and flow conditions, and agreement within three percent is shown. The usefulness of this method for preliminary design trade-off studies is demonstrated by comparison with a one-fifth scale cold-flow facility. Finally, the factors that contribute to performance degradation are identified and quantified. It is shown that the primary factor limiting performance is the nonuniformity in the exit momentum flux.

High Speed Visualization and PIV Measurements in the Near Field of Spray Produced by Flow-Blurring Atomization

2014 ◽  
Author(s):  
Lulin Jiang ◽  
Ajay K. Agrawal ◽  
Robert P. Taylor
Keyword(s):  
High Speed ◽  
Flow Direction ◽  
Near Field ◽  
Liquid Fuels ◽  
Two Phase ◽  
Time Resolved ◽  
Straight Vegetable Oil ◽  
Image Velocimetry ◽  
Fine Spray ◽  
Field Plots

Clean and stable combustion of alternative liquid fuels, such as biodiesel, straight vegetable oil and glycerol has been achieved in past studies by using a novel flow blurring (FB) injector without fuel pre-processing or combustor hardware modification. FB injector employs aerodynamic principle to form two phase flow immediately upstream of the injector exit. Explosion of air bubbles at the injector exit atomizes the liquid into a fine spray. In this study, the flow field in the near field of the FB injector is investigated by high-speed visualization and time-resolved Particle Image Velocimetry (PIV) techniques. Experiments are performed using water and air for air to liquid mass ratio (ALR) of 2. Flow visualization at the injector exit focused on field of view with the dimension of 2.3 mm × 1.4 mm, spatial resolution of 7.16 μm per pixel, exposure time of 1 μs, and image acquisition rate of 100 k frames per second (fps). Image sequence illustrates fine spray of FB atomization in the near field and the break-down process of larger droplets appearing occasionally. Time-resolved PIV technique is applied to quantify the injector near field. Plots of instantaneous, mean, root-mean-square velocities and turbulence kinetic energy are presented to reveal the droplet characteristics and secondary atomization process. Results show that the majority of the liquid is atomized into fine droplets at the injector exit. The droplet velocity increases in the flow direction and decreases from the center to the periphery of the spray. This result is consistent with the size of the droplets, i.e., the larger droplets move slowly while the finer droplets move faster as they follow the atomizing air flow.

Load Spectrum Compiling and Fatigue Life Estimation of the Automobile Wheel Hub

2020 ◽  
Vol 13 ◽  
Author(s):  
Xintian Liu ◽  
Yang Qu ◽  
Xiaobing Yang ◽  
Yongfeng Shen
Keyword(s):  
Fatigue Life ◽  
High Speed ◽  
Two Dimensional ◽  
Load Spectrum ◽  
One Dimensional ◽  
Life Estimation ◽  
Load Spectra ◽  
Fatigue Life Estimation ◽  
Program Load Spectrum ◽  
Program Load

Background:: In the process of high-speed driving, the wheel hub is constantly subjected to the impact load from the ground. Therefore, it is important to estimate the fatigue life of the hub in the design and production process. Objective:: This paper introduces a method to study the fatigue life of car hub based on the road load collected from test site. Methods:: Based on interval analysis, the distribution characteristics of load spectrum are analyzed. The fatigue life estimation of one - dimensional and two - dimensional load spectra is compared by compiling load spectra. Results:: According to the S-N curve cluster and the one-dimensional program load spectrum, the estimated range fatigue life of the hub is 397,100 km to 529,700 km. For unsymmetrical cyclic loading, each level means and amplitude of load were obtained through the Goodman fatigue empirical formula, and then according to S-N curve clusters in the upper and lower curves and two-dimensional program load spectrum, estimates the fatigue life of wheel hub of the interval is 329900 km to 435200 km, than one-dimensional load spectrum fatigue life was reduced by 16.9% - 17.8%. Conclusion:: This paper lays a foundation for the prediction of fatigue life and the bench test of fatigue durability of auto parts subjected to complex and variable random loads. At the same time, the research method can also be used to estimate the fatigue life of other bearing parts or high-speed moving parts and assemblies.

scholarly journals Modification of Airflow Structure Due to Wave Breaking on a Submerged Topography

2021 ◽  
Author(s):  
Petter Vollestad ◽  
Atle Jensen
Keyword(s):  
Wind Wave ◽  
Separated Flow ◽  
Flow Region ◽  
Breaking Waves ◽  
Leeward Side ◽  
Geometrical Properties ◽  
Image Velocimetry ◽  
Wind Profiles ◽  
The Waves ◽  
Sheltered Area

AbstractExperimental results from a combined wind–wave tank are presented. Wind profiles and resulting wind–wave spectra are described, and an investigation of the airflow above breaking waves is presented. Monochromatic waves created by the wave maker are directed towards a submerged topography. This causes the waves to break at a predictable location, facilitating particle-image-velocimetry measurements of the airflow above steep breaking and non-breaking waves. We analyze how the breaking state modifies the airflow structure, and in particular the extent of the sheltered area on the leeward side of the waves. Results illustrate that while the geometrical properties of the waves greatly influence the airflow structure on the leeward side of the waves, the state of breaking (i.e., whether the waves are currently in a state of active breaking) is not observed to have a clear effect on the extent of the separated flow region, or on the velocity distribution within the sheltered region.

Numerical assessment on the performance of variable area single- and two-stage ejectors: A comparative study

2021 ◽  
pp. 095440892110331
Author(s):  
Anil Kumar ◽  
Virendra Kumar ◽  
PMV Subbarao ◽  
Surendra K Yadav ◽  
Gaurav Singhal
Keyword(s):  
Change Theory ◽  
Single Stage ◽  
Two Stage ◽  
Entrainment Ratio ◽  
Ansys Fluent ◽  
One Dimensional ◽  
Flow Parameters ◽  
Constant Rate ◽  
Numerical Assessment ◽  
The One

The two-stage ejector has been suggested to replace the single-stage ejector geometrical configuration better to utilize the discharge flow’s redundant momentum to induce secondary flow. In this study, the one-dimensional gas dynamic constant rate of momentum change theory has been utilized to model a two-stage ejector along with a single-stage ejector. The proposed theory has been utilized in the computation of geometry and flow parameters of both the ejectors. The commercial computational fluid dynamics tool ANSYS-Fluent 14.0 has been utilized to predict performance and visualize the flow. The performance in terms of entrainment ratio has been compared under on- design and off-design conditions. The result shows that the two-stage ejector configuration has improved (≈57%) entrainment capacity than the single-stage ejector under the on-design condition.

Thermally developing forced convection flow through porous concentric pipes annular duct

2021 ◽  
pp. 095440622110022
Author(s):  
Farhan Ahmed
Keyword(s):  
Flow Region ◽  
Axial Direction ◽  
Darcy Number ◽  
Convection Flow ◽  
Axial Distance ◽  
Cross Sectional ◽  
Developing Flow ◽  
Annular Sector ◽  
Flow Through ◽  
The Cross

This article shows the thermally developing flow through concentric pipes annular sector duct by describing the Darcy Brinkman flow field. The cross sectional convection-diffusion terms are transformed in power law discretized form by integrating over the differential volume, whereas backward difference scheme is used in the axial direction of heat flow. With the help of semi implicit method for pressure linked equations-revised ( SIMPLE-R), we get the solution of the governing problem. The graphs of velocity profiles against R and average Nusselt number against axial distance are plotted for different values of Darcy number and geometrical configuration parameters. It has been pointed out that velocity and thermal entrance length decrease, when we decrease the value of Darcy number. By decreasing the cross section of the concentric pipes annular sector duct in the transverse direction, thermally fully developed flow region develops earlier.

Sign in / Sign up

Export Citation Format

Share Document