A PIV investigation of the characteristics of micro-scale synthetic jets

2007 ◽  
Vol 111 (1122) ◽  
pp. 519-528 ◽  
Author(s):  
F. Guo ◽  
S. Zhong
Keyword(s):  
Threshold Value ◽  
Stokes Number ◽  
Synthetic Jets ◽  
Operating Conditions ◽  
Performance Parameters ◽  
Stroke Length ◽  
Micro Scale ◽  
Linear Relationships ◽  
Macro Scale ◽  
Scaling Parameters

AbstractAlthough macro-scale synthetic jets are well studied, our knowledge of the behaviour of micro-scale synthetic jets is still extremely limited due to the difficulty in performing detailed measurements with a desirable spatial solution. In the work presented in this paper, a PIV study of the characteristics of synthetic jets issued into quiescent air from orifices of 5mm and 0·5mm diameter respectively is undertaken. It is found that the vortex rollup is much weaker for the 0·5mm jets due to their low Stokes number which results in a near parabolic exit velocity profile. To ensure an appreciable vortex rollup that is desirable for effective flow control, the actuator has to be operated at much higher frequencies to ensure that the Stokes number is greater than a certain threshold value. Furthermore the study shows that the characteristics of synthetic jets of different scales are identical when the dimensionless stroke length (L), Stokes number (S) and Reynolds number (ReL) are the same. On the basis of these scaling parameters, the finding acquired from the studies on macro-scale actuators can be applicable to micro-scale actuators, which are more difficult to measure. Finally, it is also found that although the linear relationships between (Land ReL) and actuator operating conditions observed for macro-scale synthetic jets are no longer valid for micro-scale synthetic jets, the linear relationships between the dimensionless jet performance parameters and (Land ReL) still exist for micro-scale synthetic jets.

The performance of round synthetic jets in quiescent flow

2006 ◽  
Vol 110 (1108) ◽  
pp. 385-393 ◽  
Author(s):  
M. Jabbal ◽  
J. Wu ◽  
S. Zhong
Keyword(s):  
Near Field ◽  
Jet Flow ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Operating Conditions ◽  
Stroke Length ◽  
Synthetic Jet Actuators ◽  
Macro Scale ◽  
Jet Actuators ◽  
The Impact

AbstractPIV measurements in the near-field region of a jet flow emanating from a round synthetic jet actuator into quiescent air were conducted over a range of operating conditions. The primary purpose of this work was to investigate the nature of synthetic jets at different operating conditions and to examine the jet flow parameters that dictate the behaviour of synthetic jet actuators. The effects of varying diaphragm displacement and oscillatory frequency for fixed actuator geometry were studied. It was observed that the characteristics of synthetic jets are largely determined by the Reynolds number and stroke length. An increase in the former is observed to increase the strength of consecutive vortex rings that compose a synthetic jet, whereas an increase in the latter results in an increase in relative vortex ring spacing and for further increases in stroke length, shedding of secondary vortices. Correlations were also made between the operating parameters and the performance parameters most effective for flow control and which therefore determine the impact of a synthetic jet on an external flow. Relations of time-averaged dimensionless mass flux, momentum flux and circulation with the jet flow conditions were established and found to widely support an analytical performance prediction model described in this paper. It is anticipated that the experimental data obtained in this study will also contribute towards providing a PIV database for macro-scale synthetic jet actuators.

scholarly journals On the Two-Scale Modelling of Elastohydrodynamic Lubrication in Tilted-Pad Bearings

Lubricants ◽  
2018 ◽  
Vol 6 (3) ◽  
pp. 78 ◽  
Author(s):  
Gregory de Boer ◽  
Andreas Almqvist
Keyword(s):  
Surface Topography ◽  
Load Capacity ◽  
Three Dimensional ◽  
Elastohydrodynamic Lubrication ◽  
Multiscale Methods ◽  
Operating Conditions ◽  
Real Surface ◽  
Micro Scale ◽  
Macro Scale ◽  
Heterogeneous Multiscale

A two-scale method for modelling the Elastohydrodynamic Lubrication (EHL) of tilted-pad bearings is derived and a range of solutions are presented. The method is developed from previous publications and is based on the Heterogeneous Multiscale Methods (HMM). It facilitates, by means of homogenization, incorporating the effects of surface topography in the analysis of tilted-pad bearings. New to this article is the investigation of three-dimensional bearings, including the effects of both ideal and real surface topographies, micro-cavitation, and the metamodeling procedure used in coupling the problem scales. Solutions for smooth bearing surfaces, and under pure hydrodynamic operating conditions, obtained with the present two-scale EHL model, demonstrate equivalence to those obtained from well-established homogenization methods. Solutions obtained for elastohydrodynamic operating conditions, show a dependency of the solution to the pad thickness and load capacity of the bearing. More precisely, the response for the real surface topography was found to be stiffer in comparison to the ideal. Micro-scale results demonstrate periodicity of the flow and surface topography and this is consistent with the requirements of the HMM. The means of selecting micro-scale simulations based on intermediate macro-scale solutions, in the metamodeling approach, was developed for larger dimensionality and subsequent calibration. An analysis of the present metamodeling approach indicates improved performance in comparison to previous studies.

An Experimental and Numerical Study of a Micro-Synthetic Jet in a Shallow Cavity

2008 ◽  
Author(s):  
Alexander Sinclair ◽  
Victoria Timchenko ◽  
John Reizes ◽  
Gary Rosengarten ◽  
Eddie Leonardi
Keyword(s):  
Numerical Study ◽  
Experimental Studies ◽  
Maximum Velocity ◽  
Stokes Number ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Numerical Results ◽  
Transfer Rates ◽  
Micro Scale ◽  
Shallow Cavity

By disrupting laminar flow, micro-scale synthetic jets have the potential to significantly increase mixing and heat transfer rates in micro-devices. Due to the difficulty involved in performing measurements on the micro-scale, few experimental studies of micro-synthetic jets exist. In this paper we describe instantaneous velocity fields obtained by μPIV measurements in the vicinity of a synthetic jet orifice 24 μm in diameter issuing into a confined geometry. Numerical results for a synthetic jet operating under similar conditions have been used to help validate and clarify the experimental results. Comparisons between the experimental and numerical results during the expulsion phase of the actuator cycle for a synthetic jet with a Reynolds number (based on maximum velocity), Re = 239 and Stokes number, S = 9, indicate there is good agreement, thereby demonstrating that the μPIV technique can be used successfully for future studies. Experimental difficulties encountered are presented and methods of overcoming them discussed.

An experimental study on the behaviours of circular synthetic jets at low Reynolds numbers

2012 ◽  
Vol 226 (11) ◽  
pp. 2686-2700 ◽  
Author(s):  
Qingfeng Xia ◽  
Shan Zhong
Keyword(s):  
Reynolds Number ◽  
Silicone Oil ◽  
Reynolds Numbers ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Operating Conditions ◽  
Flow Visualisation ◽  
Stroke Length ◽  
Low Reynolds Numbers ◽  
Low Reynolds

In the work presented in this article, the behaviour of circular synthetic jets issuing into quiescent surrounding fluid at low Reynolds numbers is experimentally studied for potential mixing applications of synthetic jets at micro-scales or in highly viscous fluids. Sugar solutions and silicone oil are used as the flow media in order to achieve the required low Reynolds numbers. The conditions for jet instability, vortex rollup and synthetic jet formation are investigated using both flow visualisation techniques and particle image velocimetry, and the typical behaviour of synthetic jets at a Reynolds number around unity is also illustrated. The roles of Reynolds number, dimensionless stroke length and Stokes number in determining the characteristics of synthetic jets are examined and found to be largely consistent with the finding obtained at higher Reynolds numbers. Finally, a parameter map of synthetic jet flow patterns is produced based on the results from this study, which can be used to aid the choice of synthetic jet operating conditions for specific applications or anticipate if a desired vortex structure can be obtained at a given synthetic jet operating condition.

Power Test System Development and Dynamic Performance State Estimation Based on Hub Motor Vehicle

2020 ◽  
Vol 13 (2) ◽  
pp. 126-140
Author(s):  
Jing Gan ◽  
Xiaobin Fan ◽  
Zeng Song ◽  
Mingyue Zhang ◽  
Bin Zhao
Keyword(s):  
Real Time ◽  
Dynamic Performance ◽  
Test System ◽  
Operating Conditions ◽  
Motor Vehicles ◽  
Maximum Speed ◽  
Performance Parameters ◽  
Power Performance ◽  
Power Test ◽  
The Real

Background: The power performance of an electric vehicle is the basic parameter. Traditional test equipment, such as the expensive chassis dynamometer, not only increases the cost of testing but also makes it impossible to measure all the performance parameters of an electric vehicle. Objective: A set of convenient, efficient and sensitive power measurement system for electric vehicles is developed to obtain the real-time power changes of hub-motor vehicles under various operating conditions, and the dynamic performance parameters of hub-motor vehicles are obtained through the system. Methods: Firstly, a set of on-board power test system is developed by using virtual instrument (Lab- VIEW). This test system can obtain the power changes of hub-motor vehicles under various operating conditions in real-time and save data in real-time. Then, the driving resistance of hub-motor vehicles is analyzed, and the power performance of hub-motor vehicles is studied in depth. The power testing system is proposed to test the input power of both ends of the driving motor, and the chassis dynamometer is combined to test so that the output efficiency of the driving motor can be easily obtained without disassembly. Finally, this method is used to carry out the road test and obtain the vehicle dynamic performance parameters. Results: The real-time current, voltage and power, maximum power, acceleration time and maximum speed of the vehicle can be obtained accurately by using the power test system in the real road experiment. Conclusion: The maximum power required by the two motors reaches about 9KW, and it takes about 20 seconds to reach the maximum speed. The total power required to maintain the maximum speed is about 7.8kw, and the maximum speed is 62km/h. In this article, various patents have been discussed.

scholarly journals 2D-wavelet based micro and macro texture analysis for asphalt pavement under snow or ice condition

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Feng Li ◽  
Gulnigar Ablat ◽  
Siqi Zhou ◽  
Yixin Liu ◽  
Yufeng Bi ◽  
...  
Keyword(s):  
Wavelet Transform ◽  
Asphalt Pavement ◽  
Asphalt Mixture ◽  
Micro Scale ◽  
Braking System ◽  
Macro Scale ◽  
Texture Characteristics ◽  
The Mean ◽  
Resistance Performance

AbstractIn ice and snow weather, the surface texture characteristics of asphalt pavement change, which will significantly affect the skid resistance performance of asphalt pavement. In this study, five asphalt mixture types of AC-5, AC-13, AC-16, SMA-13, SMA-16 were prepared under three conditions of the original state, ice and snow. In this paper, a 2D-wavelet transform approach is proposed to characterize the micro and macro texture of pavement. The Normalized Energy (NE) is proposed to describe the pavement texture quantitatively. Compared with the mean texture depth (MTD), NE has the advantages of full coverage, full automation and wide analytical scale. The results show that snow increases the micro-scale texture because of its fluffiness, while the formation of the ice sheets on the surface reduces the micro-scale texture. The filling effect of snow and ice reduces the macro-scale texture of the pavement surface. In a follow-up study, the 2D-wavelet transform approach can be applied to improve the intelligent driving braking system, which can provide pavement texture information for the safe braking strategy of driverless vehicles.

scholarly journals Component-Oriented Modeling of a Micro-Scale Organic Rankine Cycle System for Waste Heat Recovery Applications

2021 ◽  
Vol 11 (5) ◽  
pp. 1984
Author(s):  
Ramin Moradi ◽  
Emanuele Habib ◽  
Enrico Bocci ◽  
Luca Cioccolanti
Keyword(s):  
Electric Power ◽  
Heat Recovery ◽  
Waste Heat Recovery ◽  
Waste Heat ◽  
Organic Rankine Cycle ◽  
Rankine Cycle ◽  
Operating Conditions ◽  
Working Fluid ◽  
Pump Efficiency ◽  
Micro Scale

Organic Rankine cycle (ORC) systems are some of the most suitable technologies to produce electricity from low-temperature waste heat. In this study, a non-regenerative, micro-scale ORC system was tested in off-design conditions using R134a as the working fluid. The experimental data were then used to tune the semi-empirical models of the main components of the system. Eventually, the models were used in a component-oriented system solver to map the system electric performance at varying operating conditions. The analysis highlighted the non-negligible impact of the plunger pump on the system performance Indeed, the experimental results showed that the low pump efficiency in the investigated operating range can lead to negative net electric power in some working conditions. For most data points, the expander and the pump isentropic efficiencies are found in the approximate ranges of 35% to 55% and 17% to 34%, respectively. Furthermore, the maximum net electric power was about 200 W with a net electric efficiency of about 1.2%, thus also stressing the importance of a proper selection of the pump for waste heat recovery applications.

scholarly journals STOCHASTIC CARBON EMISSION ESTIMATION METHOD FOR CONSTRUCTION OPERATION

2016 ◽  
Vol 23 (1) ◽  
pp. 137-149 ◽  
Author(s):  
Chang-Yong YI ◽  
Han-Seong GWAK ◽  
Dong-Eun LEE
Keyword(s):  
Carbon Emission ◽  
Performance Metrics ◽  
Ghg Emissions ◽  
Estimation Method ◽  
Operating Conditions ◽  
Analysis Tool ◽  
Micro Scale ◽  
Work Tasks ◽  
Emission Estimation ◽  
Construction Operation

Low carbon construction is an important operation management goal because greenhouse gas (GHG) reduc­tion has become a global concern. Major construction resources that contribute GHG, such as equipment and labour, are being targeted to achieve this goal. The GHG emissions produced by the resources vary with their operating conditions. It is commendable to provide a statistical GHG emission estimation method that models the transitory nature of resource states at micro-scale of construction operations. This paper proposes a computational method called Stochastic Carbon Emission Estimation (SCE2) that measures the variability of GHG emissions. It creates construction operation models consisting of atomic work tasks, utilizes hourly equipment fuel consumption and hourly labourer respiratory rates that change according to their operating conditions classified into five categories, and identifies an optimal resource combi­nation by trading off eco-economic performance metrics such as the amount of GHG emissions, operation completion time, operation completion cost, and productivity. The study is of value to researchers because SCE2 fill in a gap to eco-economic operation modelling and analysis tool which considers operating conditions at micro-scale of construction operation having many stochastic work tasks. This study is also relevance to practitioners because it allows project man­agers to achieve eco-economic goals while honouring predefined constraints associated with time and cost.

Spatial-Pattern-Induced Evolution of a Self-Replicating Loop Network

2006 ◽  
Vol 12 (4) ◽  
pp. 461-485 ◽  
Author(s):  
Keisuke Suzuki ◽  
Takashi Ikegami
Keyword(s):  
Pattern Formation ◽  
Spatial Pattern ◽  
Spatial Patterns ◽  
Spiral Structure ◽  
Scale Interactions ◽  
Micro Scale ◽  
Macro Scale ◽  
Loop Network ◽  
Spatial Pattern Formation

We study a system of self-replicating loops in which interaction rules between individuals allow competition that leads to the formation of a hypercycle-like network. The main feature of the model is the multiple layers of interaction between loops, which lead to both global spatial patterns and local replication. The network of loops manifests itself as a spiral structure from which new kinds of self-replicating loops emerge at the boundaries between different species. In these regions, larger and more complex self-replicating loops live for longer periods of time, managing to self-replicate in spite of their slower replication. Of particular interest is how micro-scale interactions between replicators lead to macro-scale spatial pattern formation, and how these macro-scale patterns in turn perturb the micro-scale replication dynamics.

scholarly journals Experimental study of the effects of wire EDM on the characteristics of ferritic steel, at a micro-scale on the contour cut surface

2018 ◽  
Vol 115 (4) ◽  
pp. 413
Author(s):  
Nida Naveed
Keyword(s):  
Residual Stress ◽  
Stress Measurement ◽  
Surface Characteristics ◽  
Surface Damage ◽  
Cutting Process ◽  
Contour Method ◽  
X Ray Diffraction ◽  
Micro Scale ◽  
Macro Scale ◽  
Cut Surface

This study, on a micro-scale, of the WEDM cut surfaces of specimens to which the contour method of residual stress measurement is being applied provides detailed information about the effects of the cutting process on the surface quality. This is defined by a combination of several parameters: variation in surface contour profile, sub-surface damage and surface texture. Measurements were taken at the start, the middle and at the end of the cut. This study shows that during WEDM cutting, a thin layer, extending to a depth of a few micrometres below the surface of the cut, is transformed. This layer is known as the recast layer. Using controlled-depth etching and X-ray diffraction, it is shown that this induces an additional tensile residual stress, parallel to the plane of the cut surface. The WEDM cut surface and sub-surface characteristics are also shown to vary along the length of the cut. Moreover, these micro-scale changes were compared with macro-scale residual stress results and provides an indication of the point at which the changes occurred by cutting process can be significantly relative to the macro-scale residual stress in a specimen.

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