Parametric Study of Acoustic Excitation-Based Glycerol-Water Microsphere Fabrication in Single Nozzle Jetting

2010 ◽  
Vol 132 (5) ◽  
Author(s):  
C. Leigh Herran ◽  
Wei Wang ◽  
Yong Huang ◽  
Vladimir Mironov ◽  
Roger Markwald
Keyword(s):  
Excitation Frequency ◽  
Stream Velocity ◽  
Acoustic Excitation ◽  
Pressure Amplitude ◽  
Multicellular Spheroids ◽  
Glycerol Water ◽  
Volume Percentage ◽  
Precise Control ◽  
Carrier Stream ◽  
Microsphere Size

Microspheres or droplets are increasingly finding various biomedical applications as drug microspheres and multicellular spheroids. Single nozzle-based continuous jetting with the help of acoustic excitation and/or carrier stream is a basic process for monodisperse microsphere fabrication. Precise control of microsphere size and size distribution in single nozzle jetting is still of great manufacturing interest. The objective of this study is to numerically model a glycerol-water microsphere fabrication process during acoustic excitation-based single nozzle continuous jetting. Using a volume of fluid method, this study has investigated the effects of material properties and fabrication conditions such as the acoustic excitation frequency and amplitude and the carrier stream velocity on the size of microspheres fabricated. (1) The microsphere diameter decreases as the glycerol volume percentage increases. (2) The excitation frequency and pressure have a pronounced effect on the microsphere size. The microsphere diameter decreases as the excitation frequency increases, and the microsphere diameter increases with the excitation pressure amplitude. (3) The microsphere size decreases as the carrier stream velocity increases.

Effects of Acoustic Excitation on a Swirling Diffusion Flame

2010 ◽  
Vol 132 (12) ◽  
Author(s):  
Michael E. Loretero ◽  
Rong F. Huang
Keyword(s):  
Flow Field ◽  
Bluff Body ◽  
Excitation Frequency ◽  
Excitation Amplitude ◽  
Mie Scattering ◽  
Flame Length ◽  
Laser Doppler Velocimeter ◽  
Scattering Method ◽  
Acoustic Excitation ◽  
Characteristic Modes

A swirling double concentric jet is commonly used for nonpremixed gas burner application for safety reasons and to improve the combustion performance. Fuel is generally spurted at the central jet while the annular coflowing air is swirled. They are normally separated by a blockage disk where the bluff-body effects further enhance the recirculation of hot gas at the reaction zone. This paper aims to experimentally investigate the behavior of flame and flow in a double concentric jet combustor when the fuel supply is acoustically driven. Laser-light sheet assisted Mie scattering method has been used to visualize the flow, while the flame lengths were measured by a conventional photography technique. The fluctuating velocity at the jet exit was measured by a two-component laser Doppler velocimeter. Flammability and stability at first fuel tube resonant frequency are reported and discussed. The evolution of flame profile with excitation level is presented and discussed, together with the reduction in flame length. The flame in the unforced reacting axisymmetric wake is classified into three characteristic modes, which are weak swirling flame, lifted flame, and transitional reattached flame. These terms reflect their primary features of flame appearances, and when the acoustic excitation is applied, the flame behaviors change with the excitation frequency and amplitude. Four additional characteristic modes are identified; e.g., at low excitation amplitudes, wrinkling flame with a blue annular film is observed because the excitation induces vortices in the central fuel jet and hence gives rise to the wrinkling of flame. The central jet vortices become larger with the increase in excitation amplitude and thus lead to a wider and shorter flame. If the excitation amplitude is increased above a certain value, the central jet vortices change the rotation direction and pacing with the annular jet vortices. These changes in the flow field induce large turbulent intensity and mixing and therefore make the flame looks blue and short. Further increase in the excitation amplitude would lift the flame because the flow field would be dramatically modified.

The local extinction and the nonlinear behaviors of a premixed methane/air flame under low-frequency acoustic excitation

2020 ◽  
Vol 34 (13) ◽  
pp. 2050138 ◽  
Author(s):  
Yongchao Sun ◽  
Mingbo Sun ◽  
Jiajian Zhu ◽  
Yang Xie ◽  
Hongbo Wang ◽  
...  
Keyword(s):  
High Speed ◽  
Excitation Frequency ◽  
Dominant Frequency ◽  
Local Extinction ◽  
Acoustic Excitation ◽  
Flame Extinction ◽  
Buoyant Force ◽  
Hot Gas ◽  
Nature Frequency ◽  
Production Zone

The local extinction and the nonlinear behavior of a premixed methane/air flame under acoustic excitation are investigated experimentally. High-speed photography and high-speed schlieren imaging are used to investigate the oscillation characteristics of the premixed methane/air flame. The flame structure shows a periodic fluctuation when the acoustic excitation is performed to the flame. The local flame extinction can be observed during the flame evolution process. During the local flame extinction process, the flame is found to be cut into two components, then the downstream one extinguishes shortly. The Particle Image Velocimetry (PIV) results suggest that the lower velocity at the separation point is one of the reasons for the flame local extinction. The flame without the acoustic excitation oscillates with a dominant frequency of 18 Hz, which is shown by the schlieren images to be related to the evolution of the hot gas around the flame driven by the buoyant force. When the acoustic excitation frequency is 100 Hz, the structure of the hot gas is destroyed, meanwhile the amplitude of the nature frequency decreases significantly. The hot gas structure appears regularly with the increasing excitation frequency. As a result, the amplitude of the nature frequency also increases gradually. Proper Orthogonal Decomposition (POD) analysis shows that the dominant frequency of the flame without the acoustic excitation is mainly caused by the evolution of the production zone of the flame and the fluctuation of the flame tip. The evolution of the production zone is driven by the buoyant force, which indicates that the result from POD method is consistent with the conclusion obtained from the high-speed schlieren images. Two dominant modes are obtained when the excitation frequencies are 100 and 200 Hz. The two modes are mainly caused by the process of the local flame extinction and the increasing flame length.

Flow Field and Vibration Behavior of Straight Transonic Compressor Cascade due to External Acoustic Excitation

2013 ◽  
Author(s):  
Manlu Li ◽  
Anping Hou ◽  
Xiaodong Yang ◽  
Mingming Zhang ◽  
Peng Wang
Keyword(s):  
Flow Field ◽  
Excitation Frequency ◽  
Experimental Studies ◽  
Attack Angle ◽  
Mode Shapes ◽  
Acoustic Excitation ◽  
Fe Model ◽  
Compressor Cascade ◽  
Time Step ◽  
Vibration Behavior

A fluid-structure coupled approach is utilized to study the influence of external acoustic excitation on straight compressor cascade flow field and blade vibration behavior. Interaction between fluid and structure are dealt with in a coupled manner, based on the interface exchange of information between the aerodynamic and structural model. The computation fluid mesh is updated at every time step with an improved algebraic method. The flow field of cascade with/without external acoustic excitation is carried out using a 3D unsteady CFD model based on moving boundary way, as well as some experimental studies based on transonic wind tunnel. Then coupled with blade FE model, mode shapes, frequencies, vibration stress and the structural deformations of blade are identified. The performance of the cascade is obtained by computational and experimental ways, consistency of numerical and test results shows that the numerical model is suitable. The numerical results show that acoustic excitation has a greater impact on negative and designed attack angle in contrast to high positive attack angle. The cascade wake and blade surface pressure frequency characteristic are changed and the main frequency is almost the same as the acoustic excitation frequency. Compared results with no excitation, the vibration characteristics of the blade is changed, also the vibration behavior is sensitive to the excitation amplitude and frequency.

Heat Exchange Characteristics in Heat Supply and Heat Removal Parts of a Nonisothermal Circuit, Including Temperature and Velocity Fields in a HLMC Flow, for Controlled Impurity Content

2009 ◽  
Author(s):  
O. O. Novozhilova ◽  
A. V. Beznosov ◽  
S. Yu. Savinov ◽  
M. A. Antonenkov
Keyword(s):  
Heat Exchange ◽  
Oxygen Content ◽  
Velocity Structure ◽  
Experimental Studies ◽  
Heat Removal ◽  
Impurity Content ◽  
Stream Velocity ◽  
Carrier Stream ◽  
Temperature And Velocity Fields ◽  
Annular Clearance

Results of the experimental studies of the heat exchange to the lead heat-transfer agent in the annular clearance in the circulation contour with the controlled and operated processes of mass exchange and mass transfer of the oxygen content are presented. And results of experimental research of lead-bismuth heat-carrier stream velocity structure at a varied content of oxygen content are presented.

scholarly journals Dynamic Analysis of Shells

1995 ◽  
Vol 2 (5) ◽  
pp. 413-426 ◽  
Author(s):  
Charles R. Steele ◽  
Jason A. Tolomeo ◽  
Deborah E. Zetes
Keyword(s):  
Excitation Frequency ◽  
Computer Code ◽  
Material Behavior ◽  
Shell Structures ◽  
Acoustic Excitation ◽  
Rigid Surface ◽  
Implicit Methods ◽  
Shell Surface ◽  
Fine Mesh ◽  
Broad Overview

Shell structures are indispensable in virtually every industry. However, in the design, analysis, fabrication, and maintenance of such structures, there are many pitfalls leading to various forms of disaster. The experience gained by engineers over some 200 years of disasters and brushes with disaster is expressed in the extensive archival literature, national codes, and procedural documentation found in larger companies. However, the advantage of the richness in the behavior of shells is that the way is always open for innovation. In this survey, we present a broad overview of the dynamic response of shell structures. The intention is to provide an understanding of the basic themes behind the detailed codes and stimulate, not restrict, positive innovation. Such understanding is also crucial for the correct computation of shell structures by any computer code. The physics dictates that the thin shell structure offers a challenge for analysis and computation. Shell response can be generally categorized by states of extension, inextensional bending, edge bending, and edge transverse shear. Simple estimates for the magnitudes of stress, deformation, and resonance in the extensional and inextensional states are provided by ring response. Several shell examples demonstrate the different states and combinations. For excitation frequency above the extensional resonance, such as in impact and acoustic excitation, a fine mesh is needed over the entire shell surface. For this range, modal and implicit methods are of limited value. The example of a sphere impacting a rigid surface shows that plastic unloading occurs continuously. Thus, there are no short cuts; the complete material behavior must be included.

Effect of excitation frequency on flow characteristics around a square cylinder with a synthetic jet positioned at front surface

2019 ◽  
Vol 880 ◽  
pp. 764-798 ◽  
Author(s):  
Yuan Qu ◽  
Jinjun Wang ◽  
Lihao Feng ◽  
Xi He
Keyword(s):  
Flow Field ◽  
Excitation Frequency ◽  
Front Surface ◽  
Synthetic Jet ◽  
The Other ◽  
Stream Velocity ◽  
Square Cylinder ◽  
Stroke Length ◽  
Recirculation Bubble ◽  
Upstream Flow

The flow over a square cylinder controlled by a slot synthetic jet positioned at the front surface is investigated experimentally at different excitation frequencies. The Reynolds number based on the free-stream velocity and the side length of the square cylinder is 1000. The flow visualization was conducted using the laser-induced fluorescence technique. The velocity fields upstream and downstream of the square cylinder were measured synchronously with the two-dimensional time-resolved particle image velocimetry technique. Both the evolution of vortex structures and the characteristic frequencies of upstream and downstream flow fields are presented. The flow dynamics vary significantly with the excitation frequency at a fixed stroke length. During one excitation cycle, the synthetic jet vortex pair deflects to one side and later swings to the other side at a quite small excitation frequency of $f_{e}/f_{0}=0.6$, while it only deflects toward one side and does not turn to the other side at $f_{e}/f_{0}=1.0$. Compared with the natural case, the wake characteristics for the above two cases are not changed much by the synthetic jet adopted. At a moderate excitation frequency of $f_{e}/f_{0}=2.0$, the synthetic jet deflects upwards and downwards alternatively. The upstream flow field has a dominant frequency identical to half of the excitation frequency. Under the perturbations of the synthetic jet, two wake vortex pairs are formed per shedding cycle with a shedding frequency equal to that of the square cylinder without control. At a higher excitation frequency of $f_{e}/f_{0}=3.4$, the synthetic jet keeps deflecting to one side, and the upstream flow field is governed by the excitation frequency. The flow separation on the deflected side is suppressed effectively, and no periodic vortex shedding can be observed in the wake. Statistically, the velocity profiles also change with control. The recirculation bubble length in the wake is shortened, and the time-averaged velocity fluctuation is weakened remarkably. The control effects of the synthetic jet and the continuous jet are compared in this paper when placed at the front surface of a square cylinder.

Aeroacoustic Response of a Single Cylinder With Straight Circular Fins in Cross-Flow

2015 ◽  
Vol 137 (5) ◽  
Author(s):  
Nadim Arafa ◽  
Atef Mohany
Keyword(s):  
Aspect Ratio ◽  
Acoustic Pressure ◽  
Interaction Mechanism ◽  
Cross Flow ◽  
Acoustic Resonance ◽  
Resonance Excitation ◽  
Acoustic Excitation ◽  
Pressure Amplitude ◽  
Fin Thickness ◽  
Fin Spacing

The phenomenon of sound generation has been investigated in some detail for the case of bare cylinders; however, the effect of adding fins to the cylinder on the flow–sound interaction mechanism is not yet fully understood. Thus, the aeroacoustic response of a cylinder with straight circular fins in cross-flow is investigated experimentally in this work. During the experiments, the acoustic modes of the duct housing the cylinder are self-excited due to the vortex shedding that emerges from the cylinder's surface. In order to determine the effect of different fin parameters on the onset and intensity of acoustic resonance, 14 different finned cylinders with fin thickness ranging from 0.35 to 1.5 mm and fin density ranging from 4 to 13.7 fin/in. are investigated. It is observed that the finned cylinders experience an earlier acoustic resonance and higher levels of acoustic pressure compared to their equivalent bare cylinders. Moreover, it is observed that, for constant fin spacing, the acoustic pressure amplitude increases and the acoustic resonance occurs at earlier velocities as the fin thickness increases. On the other hand, for constant fin thickness, as the fin spacing increases the amplitude of the acoustic pressure decreases while the onset of the resonance is delayed. Finally, the effect of the cylinder's aspect ratio on the acoustic resonance excitation is presented. It is shown that as the finned cylinders' aspect ratio increases from 4.85 to 11.3, the normalized acoustic pressure during resonance increases drastically. However, for bare cylinders the normalized acoustic pressure during resonance is not highly dependent on the cylinders' aspect ratio. These results indicate that adding fins to the cylinder alters the flow field downstream of the cylinder in a manner that makes it more susceptible to acoustic excitation.

Geometry Effects on the Flow Rectification of a Dynamic Micro Diffuser: A Numerical Investigation

Volume 4 ◽  
2004 ◽  
Author(s):  
Chen-Li Sun ◽  
Kun Hao Huang
Keyword(s):  
Pressure Gradient ◽  
Numerical Investigation ◽  
Flow Rate ◽  
Excitation Frequency ◽  
Fluid Flows ◽  
Volumetric Flow Rate ◽  
Reynolds Numbers ◽  
Pressure Amplitude ◽  
Half Angle ◽  
Geometry Effects

In this study, a numerical investigation is presented to characterize the geometry effects on the transient behaviors of a micro diffuser pump. Four parameters of the dynamic diffuser pump, half-angle, depth, length, and excitation frequency, are considered. A time-dependent sinusoidal pressure with fixed pressure amplitude (200 Pa) is applied at the inlet as the boundary condition. The results from the numerical analysis have been quantified in terms of average volumetric flow rate. Despite the corresponding low Reynolds numbers (Re < 10), circulation is observed for all tested half-angles. When the direction of pressure gradient switches, fluid flows against the pressure gradient and triggers flow separation near wall. The vortex then migrates from wall toward the center of diffuser with time. For 5° ≤ θ ≤ 35°, diffusers with larger half-angles show better rectification effects. For θ gt; 35°, net flow rate is nearly independent of half-angle. Shorter and deeper diffuser results in larger net flow rate regardless of its half-angle. The increase of the excitation frequency diminishes the flow rectification in micro diffuser.

scholarly journals Precise control of PLG microsphere size provides enhanced control of drug release rate

2002 ◽  
Vol 82 (1) ◽  
pp. 137-147 ◽  
Author(s):  
Cory Berkland ◽  
Martin King ◽  
Amanda Cox ◽  
Kyekyoon (Kevin) Kim ◽  
Daniel W Pack
Keyword(s):  
Drug Release ◽  
Release Rate ◽  
Drug Release Rate ◽  
Precise Control ◽  
Microsphere Size

The Effect of Acoustic Excitation on Boundary Layer Separation of a Highly Loaded LPT Blade

2012 ◽  
Author(s):  
Chiara Bernardini ◽  
Stuart Benton ◽  
Jeffrey P. Bons
Keyword(s):  
Boundary Layer ◽  
Shear Layer ◽  
Separation Bubble ◽  
Active Flow Control ◽  
Excitation Frequency ◽  
Acoustic Excitation ◽  
Intensity Level ◽  
Inlet Section ◽  
Suction Surface ◽  
Highly Loaded

An experimental investigation of the effect of acoustic excitation on the boundary layer development of a highly loaded low-pressure turbine blade at low-Reynolds number is investigated. The aim of this work is to study the effect of excitation at select frequencies on separation which could give indications about active flow control exploitation. The front-loaded L2F blade is tested in a low-speed linear cascade. The uncontrolled flow presents a separation bubble on the suction surface at Reynolds numbers below 40,000. For these conditions, the instability of the shear layer is documented using hot-wire anemometry. A loudspeaker upstream of the cascade is directed towards the passage inlet section. A parametric study on the effect of amplitude and frequency is carried out. The effect of the excitation frequency is observed to delay separation for a range of frequencies. However, the control authority of sound is found to be most effective at the fundamental frequency of the shear layer. The amplitude of perturbation is significant in the outcome of control until a threshold value is reached. PIV measurements allow a deeper understanding of the mechanisms leading to the reduction of separation. Data has been acquired with a low inlet turbulence level (<1%) in order to provide a cleaner environment which magnifies the effects of the excitation frequency, and with an increased turbulence intensity level of 3% which is representative of more typical engine values. Integrated wake loss values are also presented to evaluate the effect on blade performance.

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