Flow Field and Heat Transfer of an Impinging Synthetic Jet in the Presence of Cross-Flow: Application of SAS and DES Approaches

2021 ◽  
pp. 095440892110644
Author(s):  
Farzad Bazdidi–Tehrani ◽  
Ali Saadniya ◽  
Soroush Rashidzadeh
Keyword(s):  
Heat Transfer ◽  
Flow Velocity ◽  
Active Flow Control ◽  
Experimental Studies ◽  
Cross Flow ◽  
Numerical Data ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Detached Eddy Simulation ◽  
Cross Flow Velocity

Nowadays, synthetic jets have various applications such as cooling enhancement and active flow control. In the present paper, the capability of two turbulence modelling approaches in predicting thermal performance of an impinging synthetic jet is investigated. These two approaches are scale adaptive simulation (SAS) and detached eddy simulation (DES). Comparisons between numerical data and experimental studies reveal that the ability of DES in predicting the asymmetrical trend of heat transfer profiles is better than SAS in almost all the study cases. Although, near the stagnation zone, the performance of SAS is superior. Results show that the effects of parameters such as frequency, cross-flow velocity and suction duty cycle factor are well predicted by both approaches. An increase of cross-flow velocity from 1.81 m/s to 2.26 m/s results in an improvement of [Formula: see text] near the stagnation point by almost 16.3% and 9.2% using DES and SAS, respectively.

A Numerical Study of an Impingement Array Inside a Three Dimensional Turbine Vane

2010 ◽  
Author(s):  
Marcel Leo´n De Paz ◽  
B. A. Jubran
Keyword(s):  
Heat Transfer ◽  
Flow Velocity ◽  
Numerical Study ◽  
Cross Flow ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Average Deviation ◽  
Turbine Vane ◽  
Cross Flow Velocity ◽  
Target Spacing

A simplified impingement high pressure turbine vane is modeled and solved via Fluent. A relatively flat section of the vane is fitted with 15 0.51mm diameter impingement holes — 5 rows of 3 jets. Results are then compared to known experimental data. Two different turbulence models are used to study this preliminary configuration: K-omega SST and the RNG k-epsilon model. The jet exit Reynolds numbers, cross flow velocity, and the average and local heat transfer distribution are analyzed with varying Reynolds numbers and jet to target spacing. It is observed that the static pressure decreases across the vane with the cross flow velocity increasing towards the trailing edge exit, thereby uniformly increasing the jet exit velocity at each row. Forced convection is seen in the downstream rows in-between span-wise jets due to high cross flow velocities. All numerical results were capable of replicating the higher heat transfer obtained with a higher Reynolds number, and conversely, a lower heat transfer with an increase in jet to target spacing. In its entirety, validating against all correlations, the RNG model obtained an average deviation of 15.7%, while the K-omega SST yielded only 7.8%.

An Experimental Study of a Synthetic Jet in Cross Flow in a Microchannel

2010 ◽  
Author(s):  
Alexander Sinclair ◽  
John Reizes ◽  
Victoria Timchenko ◽  
Gary Rosengarten
Keyword(s):  
Heat Transfer ◽  
Laminar Flow ◽  
Cross Flow ◽  
Oscillatory Solution ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Square Duct ◽  
Transfer Rates ◽  
Mixing Performance ◽  
Jet In Cross Flow

Laminar flow limits the mixing performance and heat transfer rates that occurs within microdevices. Synthetic jets in the microscale could disrupt laminar flow and improve the performance of such devices. In this paper a synthetic microjet integrated in a microchannel was designed and fabricated using micromachining techniques. The channel flow was driven by a syringe pump at a rate of 1.39μL/s and the device was actuated using a piezoceramic disc at a frequency of 600Hz. Flow fields were measured phase locked to the actuation cycle using the MicroPIV technique in the mid plane of the jet. The resultant fields revealed a jet with a largest velocity of 2.3m/s. The average velocity during expulsion was estimated to be 0.73m/s using a comparison to the oscillatory solution to flow in a square duct. Measurements at different phases in the cycle revealed a jet strong enough to impinge on the opposing wall and the growth and decay of a pair of vortices formed at the edge of the orifice. It was also shown that the synthetic jet significantly altered the flow patterns showing promising signs for enhancing mixing and heat transfer in microchannels.

Interaction of Synthetic Jet Cooling Performance With Gravity and Buoyancy Driven Flows

2007 ◽  
Author(s):  
Mehmet Arik ◽  
Yogen Utturkar ◽  
Mustafa Gursoy
Keyword(s):  
Heat Transfer ◽  
Heat Dissipation ◽  
Cross Flow ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Jet Cooling ◽  
Impingement Heat Transfer ◽  
Buoyancy Driven Flows ◽  
Experimental Findings ◽  
Meso Scale

Meso scale cooling devices have been of interest for low form factor, tight space, and high COP thermal management problems. A candidate meso scale device, known as synthetic jets, operates with micro fluidic principles and disturbs the boundary layer causing significant heat transfer over conventional free convective heat transfer in air. Previous papers have dealt with the impingement and cross flow, but did not study mixed convection for synthetic jet with natural convection. In the present study, we discuss the results of an experimental study to investigate the interplay between jet orientations with respect to gravity, elevated temperature conditions, and synthetic jet heat dissipation capacity. Experiments were performed by placing synthetic at different positions around a square, 25.4mm heated flat surface. The flow physics behind the experimental findings is discussed. It is found that impingement heat transfer outperformed more than 30% compared to other orientations. The jet showed about 15% sensitivity to angular orientations.

scholarly journals Heat Transfer in Adjacent Interacting Impinging Synthetic Jets

2009 ◽  
Author(s):  
Tim Persoons ◽  
Tadhg S. O’Donovan ◽  
Darina B. Murray
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Cross Flow ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Normal Velocity ◽  
Mean Flow ◽  
Stroke Length ◽  
Cooling Performance ◽  
Single Jet

An impinging synthetic jet can attain heat transfer rates comparable to a continuous jet, without net mass input. However it needs a forced cross-flow to supply fresh cooling medium. The vectoring effect of adjacent synthetic jets allows directing the flow by changing the phase between the jets. This study uses the vectoring effect of two adjacent synthetic jets to draw in fresh air, while maintaining high impingement cooling performance. The experimental approach applies infrared thermography and particle image velocimetry to quantify the local convective heat transfer and flow field, respectively. The heat transfer profiles for various phase differences have been compared to the mean flow field and wall-normal velocity fluctuation intensity. For a fixed operating point (stroke length and Reynolds number) and geometry, the cooling performance has been optimised for phase and jet-to-surface spacing, resulting in about 90% enhancement of the maximum and overall cooling rate compared to a single jet, without the need for external cross-flow forcing.

Effects of alternating elliptical chamber on jet impingement heat transfer in vane leading edge under different cross-flow conditions

2021 ◽  
pp. 1-17
Author(s):  
K. Xiao ◽  
J. He ◽  
Z. Feng
Keyword(s):  
Heat Transfer ◽  
Velocity Ratio ◽  
Cross Flow ◽  
Leading Edge ◽  
Longitudinal Vortices ◽  
Impingement Jet ◽  
Flow And Heat Transfer ◽  
Impingement Heat Transfer ◽  
Cross Flow Velocity ◽  
The Cross

ABSTRACT This paper proposes an alternating elliptical impingement chamber in the leading edge of a gas turbine to restrain the cross flow and enhance the heat transfer, and investigates the detailed flow and heat transfer characteristics. The chamber consists of straight sections and transition sections. Numerical simulations are performed by solving the three-dimensional (3D) steady Reynolds-Averaged Navier–Stokes (RANS) equations with the Shear Stress Transport (SST) k– $\omega$ turbulence model. The influences of alternating the cross section on the impingement flow and heat transfer of the chamber are studied by comparison with a smooth semi-elliptical impingement chamber at a cross-flow Velocity Ratio (VR) of 0.2 and Temperature Ratio (TR) of 1.00 in the primary study. Then, the effects of the cross-flow VR and TR are further investigated. The results reveal that, in the semi-elliptical impingement chamber, the impingement jet is deflected by the cross flow and the heat transfer performance is degraded. However, in the alternating elliptical chamber, the cross flow is transformed to a pair of longitudinal vortices, and the flow direction at the centre of the cross section is parallel to the impingement jet, thus improving the jet penetration ability and enhancing the impingement heat transfer. In addition, the heat transfer in the semi-elliptical chamber degrades rapidly away from the stagnation region, while the longitudinal vortices enhance the heat transfer further, making the heat transfer coefficient distribution more uniform. The Nusselt number decreases with increase of VR and TR for both the semi-elliptical chamber and the alternating elliptical chamber. The alternating elliptical chamber enhances the heat transfer and moves the stagnation point up for all VR and TR, and the heat transfer enhancement is more obvious at high cross-flow velocity ratio.

Micro Fluidic Jets for Thermal Management of Electronics

Volume 4 ◽  
2004 ◽  
Author(s):  
Jivtesh Garg ◽  
Mehmet Arik ◽  
Stanton Weaver ◽  
Seyed Saddoughi
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Heated Surface ◽  
Turbulent Jets ◽  
Harmonic Signal ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Small Scale ◽  
Air Cooling ◽  
Infrared Thermal Imaging

Micro fluidics devices are conventionally used for boundary layer control in many aerospace applications. Synthetic Jets are intense small scale turbulent jets formed from entrainment and expulsion of the fluid in which they are embedded. The idea of using synthetic jets in confined electronic cooling applications started in late 1990s. These micro fluidic devices offer very efficient, high magnitude direct air-cooling on the heated surface. A proprietary synthetic jet designed in General Electric Company was able to provide a maximum air velocity of 90 m/s from a 1.2 mm hydraulic diameter rectangular orifice. An experimental study for determining the thermal performance of a meso scale synthetic jet was carried out. The synthetic jets are driven by a time harmonic signal. During the experiments, the operating frequency for jets was set between 3 and 4.5 kHz. The resonance frequency for a particular jet was determined through the effect on the exit velocity magnitude. An infrared thermal imaging technique was used to acquire fine scale temperature measurements. A square heater with a surface area of 156 mm2 was used to mimic the hot component and extensive temperature maps were obtained. The parameters varied during the experiments were jet location, driving jet voltage, driving jet frequency and heater power. The output parameters were point wise temperatures (pixel size = 30 μm), and heat transfer enhancement over natural convection. A maximum of approximately 8 times enhancement over natural convection heat transfer was measured. The maximum coefficient of cooling performance obtained was approximately 6.6 due to the low power consumption of the synthetic jets.

Experimental Investigation of the Effect of Synthetic Jets in Minichannels With Subcooled Boiling Flow

2013 ◽  
Author(s):  
David M. Sykes ◽  
Andrew L. Carpenter ◽  
Gregory S. Cole
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Local Heat Transfer ◽  
Local Heat ◽  
High Heat ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Heat Transfer Augmentation

Microchannels and minichannels have been shown to have many potential applications for cooling high-heat-flux electronics over the past 3 decades. Synthetic jets can enhance minichannel performance by adding net momentum flux into a stream without adding mass flux. These jets are produced because of different flow patterns that emerge during the induction and expulsion stroke of a diaphragm, and when incorporated into minichannels can disrupt boundary layers and impinge on the far wall, leading to high heat transfer coefficients. Many researchers have examined the effects of synthetic jets in microchannels and minichannels with single-phase flows. The use of synthetic jets has been shown to augment local heat transfer coefficients by 2–3 times the value of steady flow conditions. In this investigation, local heat transfer coefficients and pressure loss in various operating regimes were experimentally measured. Experiments were conducted with a minichannel array containing embedded thermocouples to directly measure local wall temperatures. The experimental range extends from transitional to turbulent flows. Local wall temperature measurements indicate that increases of heat transfer coefficient of over 20% can occur directly below the synthetic jet with low exit qualities. In this study, the heat transfer augmentation by using synthetic jets was dictated by the momentum ratio of the synthetic jet to the bulk fluid flow. As local quality was increased, the heat transfer augmentation dropped from 23% to 10%. Surface tension variations had a large effect on the Nusselt number, while variations in inertial forces had a small effect on Nusselt number in this operating region.

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