The Effects of the Synthetic Jet on the Mixing Promotion in Low Reynolds Number

The present paper describes a synthetic jet interaction with the cross flow in low Reynolds number condition by flow visualization and the wall static pressure measurements. The primary focus of the current study is to examine the possibility on the interaction of the synthetic jet with the cross flow in low Reynolds number viscous dominant flow. The low bulk velocity of the cross flow is set in a small scale of the wind tunnel with a high aspect ratio. A wide range of Reynolds number based on the tunnel height and the bulk velocity is covered. The flow visualization at Reynolds number of 1,000 is conducted in X-Y and Y-Z planes to clarify the development of the interaction process in the downstream. Both the time averaged and phase averaged wall static pressure were obtained downstream of the jet injection. The synthetic jet has a diameter of 0.5 mm and a frequency of 100 to 400 Hz. The penetration of the jet in the cross flow depends on the jet velocity ratio, and the deepest penetration occurs at the phase of π/2 at the highest jet velocity ratio. The counter rotating longitudinal vortex pair is generated even in low Reynolds number and can be observed at 100d downstream from the injection. The vortex pair shows the up-wash motion at the center of the jet core and the down-wash motion at the outsides of the jet. For the synthetic jet in cross flow, the fluctuated wall static pressure is increased, and the wall static pressure has similar frequency to the synthetic jet.

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Flow Characteristics of a Low Reynolds Number Jet in Crossflow with an Obstacle Block

The Open Fuels & Energy Science Journal ◽

10.2174/1876973x01609010037 ◽

2016 ◽

Vol 9 (1) ◽

pp. 37-46 ◽

Cited By ~ 1

Author(s):

Jianlong Chang ◽

Xudong Shao ◽

Xiao Hu ◽

Shuangbiao Zhang

Keyword(s):

Reynolds Number ◽

Low Reynolds Number ◽

Velocity Ratio ◽

Flow Characteristics ◽

Vortex Pair ◽

Lower Velocity ◽

Eddy Simulation ◽

Jet In Crossflow ◽

Crossflow Velocity ◽

Low Reynolds

The jet in crossflow at very low Reynolds number (Re=100) with and without block is performed by means of large eddy simulation for the jet-to-crossflow velocity ratios (r) ranging from 1 to 3, and the corresponding flow characteristics are compared. The results show that the time-averaged particle trajectories of the jet are slightly changed if a block is presented, and the mixed vortices are weakened. The existence of the block also can accelerate the formation of stable counter-rotating vortex pair. At lower velocity ratio (r=1), the block has little effect on the jet in crossflow with a symmetrically positive and negative kidney shaped vortices. As the velocity ratio increases, the effect of block not only can generate an asymmetry of positive and negative kidney shaped vortices, but also it can reinforce the interaction between the positive and negative vortices in the jet in crossflow. The effect of block on the temperature field is also analyzed in detail.

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Trajectory of a synthetic jet issuing into high-Reynolds-number turbulent boundary layers

Journal of Fluid Mechanics ◽

10.1017/jfm.2018.734 ◽

2018 ◽

Vol 856 ◽

pp. 531-551 ◽

Cited By ~ 5

Author(s):

Tim Berk ◽

Nicholas Hutchins ◽

Ivan Marusic ◽

Bharathram Ganapathisubramani

Keyword(s):

Reynolds Number ◽

Boundary Layers ◽

High Reynolds Number ◽

Velocity Ratio ◽

Cross Flow ◽

Turbulent Boundary Layers ◽

Synthetic Jet ◽

Actuation Frequency ◽

The Cross ◽

High Reynolds

Synthetic jets are zero-net-mass-flux actuators that can be used in a range of flow control applications. For some applications, the scaling of the trajectory of the jet with actuation and cross-flow parameters is important. This scaling is investigated for changes in the friction Reynolds number, changes in the velocity ratio (defined as the ratio between the mean jet blowing velocity and the free-stream velocity) and changes in the actuation frequency of the jet. A distinctive aspect of this study is the high-Reynolds-number turbulent boundary layers (up to $Re_{\unicode[STIX]{x1D70F}}=12\,800$) of the cross-flow. To our knowledge, this is the first study to investigate the effect of the friction Reynolds number of the cross-flow on the trajectory of an (unsteady) jet, as well as the first study to systematically investigate the scaling of the trajectory with actuation frequency. A broad range of parameters is varied (rather than an in-depth investigation of a single parameter) and the results of this study are meant to indicate the relative importance of each parameter rather than the exact influence on the trajectory. Within the range of parameters explored, the critical ones are found to be the velocity ratio as well as a non-dimensional frequency based on the jet actuation frequency, the cross-flow velocity and the jet dimensions. The Reynolds number of the boundary layer is shown to have only a small effect on the trajectory. An expression for the trajectory of the jet is derived from the data, which (in the limit) is consistent with known expressions for the trajectory of a steady jet in a cross-flow.

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1919 Behavior of Synthetic Jet in Cross Flow at Low Reynolds Number : Three-dimensional Measurement Using Stereo-PIV

The proceedings of the JSME annual meeting ◽

10.1299/jsmemecjo.2008.2.0_237 ◽

2008 ◽

Vol 2008.2 (0) ◽

pp. 237-238

Author(s):

Toru Iai ◽

Koichi Inose ◽

Masashi Higashiura ◽

Masahiro Motosuke ◽

Shinji Honami

Keyword(s):

Reynolds Number ◽

Low Reynolds Number ◽

Three Dimensional ◽

Cross Flow ◽

Synthetic Jet ◽

Dimensional Measurement ◽

Jet In Cross Flow ◽

Three Dimensional Measurement ◽

Low Reynolds

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Low Reynolds Number Flow Control Over an Airfoil Using Synthetic Jet Actuators

Volume 7: Fluid Flow, Heat Transfer and Thermal Systems, Parts A and B ◽

10.1115/imece2010-39728 ◽

2010 ◽

Cited By ~ 2

Author(s):

Sebastian D. Goodfellow ◽

Serhiy Yarusevych ◽

Pierre Sullivan

Keyword(s):

Boundary Layer ◽

Reynolds Number ◽

Flow Visualization ◽

Low Reynolds Number ◽

Excitation Frequency ◽

Synthetic Jet ◽

Hot Wire ◽

Synthetic Jet Actuators ◽

Jet Actuators ◽

Low Reynolds

The influence of periodic excitation from synthetic jet actuators, SJA, on boundary layer separation and reattachment over a NACA 0025 airfoil at a low Reynolds number is studied. All experiments were performed in a low-turbulence recirculating wind tunnel at a Reynolds number of 100000 and angle of attack of α = 0°. Mounted just below the surface of the airfoil, the SJA consists of four (32.77mm diameter) piezo-electric ceramic diaphragms positioned in a single row. Flow visualization and hot wire tests were conducted with the SJA outside of the airfoil to characterize the exit flow. Results from flow visualization show a vertical jet pulse accompanied by two counter rotating vortices being produced at the exit of the simulated slot, with the vortices shed at the excitation frequency. Based on flow visualization results, the length scales of successive vortices were used to estimate the exit velocities. Hot-wire measurements determined the maximum jet velocity for a range of excitation frequencies (f = 50Hz–2.7kHz) and voltages (Vp–p = 50V–300V), which was used to characterize the excitation amplitude in terms of the momentum coefficient (cμ). With the SJA installed in the airfoil, preliminary flow visualization results show a reattachment of the boundary layer and a significant reduction in wake width.

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