SYNTHETIC JET CHARACTERISTIC VELOCITY ESTIMATED ON THE BASIS OF MOMENTUM FLUX MEASUREMENT

2018 ◽  
Author(s):  
J. Kordík ◽  
Z. Trávníček
Keyword(s):  
Momentum Flux ◽  
Flux Measurement ◽  
Synthetic Jet ◽  
Characteristic Velocity

A Synthetic Jet Issuing From a Bio-Inspired Actuator With an Oscillating Nozzle Lip

2018 ◽  
Vol 140 (10) ◽  
Author(s):  
Zdeněk Trávníček ◽  
Zuzana Broučková
Keyword(s):  
Momentum Flux ◽  
Flux Measurement ◽  
Experimental Methods ◽  
Synthetic Jet ◽  
Operating Frequency ◽  
Working Fluid ◽  
Hot Wire ◽  
Synthetic Jet Actuator ◽  
Novel Variant ◽  
Flexible Diaphragm

A novel variant of a synthetic jet actuator (SJA) has been designed, manufactured, and tested. The novelty consists in a bio-inspired nozzle whose oscillating lip is formed by a flexible diaphragm rim. The working fluid is air, and the operating frequency is 65 Hz. The proposed SJA was tested by three experimental methods: phase-locked visualization of the nozzle lips, hot-wire anemometry, and momentum flux measurement using a precision scale. The results demonstrate advantages of the proposed SJA, namely, an increase in the momentum flux by 18% compared with that of a conventional SJA.

scholarly journals Novel Nozzle Shapes for Synthetic Jet Actuators Intended to Enhance Jet Momentum Flux

Actuators ◽  
2018 ◽  
Vol 7 (3) ◽  
pp. 53 ◽  
Author(s):  
Jozef Kordík ◽  
Zdeněk Trávníček
Keyword(s):  
Momentum Flux ◽  
Element Model ◽  
Velocity Profiles ◽  
Input Power ◽  
Synthetic Jet ◽  
Stroke Length ◽  
Synthetic Jet Actuator ◽  
Pressure Loss Coefficient ◽  
Nozzle Plate ◽  
Lumped Element Model

An axisymmetric synthetic jet actuator based on a loudspeaker and five types of flanged nozzles were experimentally tested and compared. The first (reference) type of nozzle was a common sharp-edged circular hole. The second type had a rounded lip on the inside. The third nozzle type was assembled from these two types of nozzles—it had a rounded lip on the inside and straight section on the outside. The fourth nozzle was assembled using orifice plates such that the rounded lips were at both inner and outer nozzle ends. The last nozzle was equipped with an auxiliary nozzle plate placed at a small distance downstream of the main nozzle. The actuators with particular nozzles were tested by direct measurement of the synthetic jet (SJ) time-mean thrust using precision scales. Velocity profiles at the actuator nozzle exit were measured by a hot-wire anemometer. Experiments were performed at eight power levels and at the actuator resonance frequency. The highest momentum flux was achieved by the nozzle equipped with an auxiliary nozzle plate. Namely, an enhancement was approximately 31% in comparison with an effect of the reference nozzle at the same input power. Furthermore, based on the cavity pressure and the experimental velocity profiles, parameters for a lumped element model (mass of moving fluid and pressure loss coefficient) were evaluated. These values were studied as functions of the dimensionless stroke length.

scholarly journals Momentum Flux Measurement on Single-Hole GDI Injector under Flash-Boiling Condition

2015 ◽  
Author(s):  
Lucio Postrioti ◽  
Maurizio Bosi ◽  
Andrea Cavicchi ◽  
Fakhry AbuZahra ◽  
Rita Di Gioia ◽  
...  
Keyword(s):  
Momentum Flux ◽  
Flux Measurement ◽  
Single Hole ◽  
Flash Boiling

Characterization of Impingement Heat/Mass Transfer to the Synthetic Jet Generated by a Biomimetic Actuator

2019 ◽  
Vol 141 (4) ◽  
Author(s):  
Zdeněk Trávníček ◽  
Zuzana Broučková
Keyword(s):  
Mass Transfer ◽  
Heat Mass Transfer ◽  
Mass Transfer Rate ◽  
Jet Impingement ◽  
Flux Measurement ◽  
Impinging Jets ◽  
Synthetic Jet ◽  
Working Fluid ◽  
Naphthalene Sublimation Technique ◽  
Flexible Diaphragm

Two biomimetic synthetic jet (SJ) actuators were designed, manufactured, and tested under conditions of a jet impingement onto a wall. Nozzles of the actuators were formed by a flexible diaphragm rim, the working fluid was air, and the operating frequencies were chosen near the resonance at 65 Hz and 69 Hz. Four experimental methods were used: phase-locked visualization of the oscillating nozzle lips, jet momentum flux measurement using a precision scale, hot-wire anemometry, and mass transfer measurement using the naphthalene sublimation technique. The results demonstrated possibilities of the proposed actuators to cause a desired heat/mass transfer distribution on the exposed wall. It was concluded that the heat/mass transfer rate was commensurable with a conventional continuous impinging jets (IJs) at the same Reynolds numbers.

Effects of vortex-induced velocity on the development of a synthetic jet issuing into a turbulent boundary layer

2019 ◽  
Vol 870 ◽  
pp. 651-679 ◽  
Author(s):  
Tim Berk ◽  
Bharathram Ganapathisubramani
Keyword(s):  
Velocity Field ◽  
Momentum Transfer ◽  
Momentum Flux ◽  
Cross Flow ◽  
Measured Data ◽  
Velocity Fields ◽  
Synthetic Jet ◽  
Vortical Structures ◽  
The Cross ◽  
Induced Velocity

A synthetic jet issuing into a cross-flow influences the local velocity of the cross-flow. At the jet exit the jet is oriented in the wall-normal direction while the cross-flow is oriented in the streamwise direction, leading to a momentum transfer between the jet and the cross-flow. Streamwise momentum transferred from the cross-flow to the jet accelerates the pulses created by the jet. This momentum transfer continuous up to some point downstream where these pulses have the same velocity as the surrounding flow and are no longer blocking the cross-flow. The momentum transfer from the cross-flow to the jet leads to a momentum deficit in the cross-flow far downstream of the viscous near field of the jet. In the literature this momentum-flux deficit is often attributed to viscous blockage or to up-wash of low-momentum fluid. The present paper proposes and quantifies a third source of momentum deficit: a velocity induced opposite to the cross-flow by the vortical structures created by the synthetic jet. These vortical structures are reconstructed from measured data and their induced velocity is calculated using the Biot–Savart law. The three-dimensional three-component induced velocity fields show great similarity to the measured velocity fields, suggesting that this induced velocity is the main contributor to the velocity field around the synthetic jet and viscous effects have only a small influence. The momentum-flux deficit induced by the vortical structures is compared to the measured momentum-flux deficit, showing that the main part of this deficit is caused by the induced velocity. Variations with Strouhal number (frequency of the jet) and velocity ratio (velocity of the jet) are observed and discussed. An inviscid-flow model is developed, which represents the downstream evolution of the jet in cross-flow. Using the measured data as an input, this model is able to predict the deformation, (wall-normal) evolution and qualitative velocity field of the jet. The present study presents evidence that the velocity induced by the vortical structures forming a synthetic jet plays an important role in the development of and the velocity field around the jet.

A Methodology for the Estimation of Hole-to-Hole Injected Mass Based on Spray Momentum Flux Measurement

2017 ◽  
Author(s):  
Alessandro Mariani ◽  
Andrea Cavicchi ◽  
Lucio Postrioti ◽  
Carmine Ungaro
Keyword(s):  
Momentum Flux ◽  
Flux Measurement

Sensible heat and momentum flux measurement with an optical inner scale meter

1997 ◽  
Vol 85 (3-4) ◽  
pp. 259-267 ◽  
Author(s):  
A.E. Green ◽  
K.J. McAneney ◽  
J.P. Lagouarde
Keyword(s):  
Momentum Flux ◽  
Flux Measurement ◽  
Sensible Heat ◽  
Inner Scale

Momentum flux measurement in boys: A clinical evaluation

1982 ◽  
Vol 1 (2) ◽  
pp. 173-179 ◽  
Author(s):  
D. J. Griffiths ◽  
R. J. Scholtmeijer
Keyword(s):  
Clinical Evaluation ◽  
Momentum Flux ◽  
Flux Measurement

scholarly journals Active Control of Tip Clearance Flow in Axial Compressors

2005 ◽  
Vol 127 (2) ◽  
pp. 352-362 ◽  
Author(s):  
Jin Woo Bae ◽  
Kenneth S. Breuer ◽  
Choon S. Tan
Keyword(s):  
Active Control ◽  
Momentum Flux ◽  
Synthetic Jet ◽  
Tip Clearance ◽  
Control Technique ◽  
Mixing Enhancement ◽  
Leakage Flow ◽  
Mean Flow ◽  
Tip Leakage ◽  
The Mean

Control of compressor tip clearance flows is explored in a linear cascade using three types of fluidic actuators; normal synthetic jet (NSJ; unsteady jet normal to the mean flow with zero net mass flux), directed synthetic jet (DSJ; injection roughly aligned with the mean flow), and steady directed jet (SDJ), mounted on the casing wall. The effectiveness of each active control technique is determined in terms of its ability to achieve: (1) reduction of tip leakage flow rate, (2) mixing enhancement between tip leakage and core flow, and (3) increase in streamwise momentum of the flow in the endwall region. The measurements show that the NSJ provides mixing enhancement only, or both mixing enhancement and leakage flow reduction, depending on its pitchwise location. The DSJ and SDJ actuators provide streamwise momentum enhancement with a consequent reduction of clearance-related blockage. The blockage reduction associated with the use of NSJ is sensitive to actuator frequency, whereas that with the use of DSJ is not. For a given actuation amplitude, DSJ and SDJ are about twice as effective as NSJ in reducing clearance-related blockage. Further the DSJ and SDJ can eliminate clearance-related blockage with a time-averaged momentum flux roughly 16% of the momentum flux of the leakage flow. However, achieving an overall gain in efficiency appears to be hard; the decrease in loss is only about 30% of the expended flow power from the present SDJ actuator. Guidelines for improving the efficiency of the directed jet actuation are presented.

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