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.

scholarly journals Numerical Studies of Propeller Exciting Bearing Forces under Nonuniform Ship’s Nominal Wake and the Influence of Cross Flows

2017 ◽  
Vol 2017 ◽  
pp. 1-15
Author(s):  
Huilan Yao ◽  
Huaixin Zhang
Keyword(s):  
Velocity Field ◽  
Flow Field ◽  
Water Surface ◽  
Free Water ◽  
Measured Data ◽  
Three Dimension ◽  
Numerical Studies ◽  
Exciting Forces ◽  
The Cross ◽  
Commercial Solver

Propeller exciting forces are the main causes of stern vibrations. In this paper, three-dimension exciting bearing forces of one blade and the whole propeller under nonuniform ship’s wake were predicted, and the influence of cross flows on these exciting forces was studied. All simulations were carried out using a commercial solver, STAR-CCM+. To obtain the nominal wake for studying propeller exciting forces, flow field around a bare hull was simulated. Numerical results were widely validated by measured data, especially the velocity field at the propeller plane. Harmonic characteristics of the nonuniform ship’s wake were studied. Then, a propeller under uniform inflow and nonuniform ship’s wake with/without cross flows was simulated. Free-water surface and hull boundary were considered using a specially designed dummy stern. Results show that the influence of cross flows on propeller exciting forces is obvious. As for the exciting forces of one blade, the cross flows have greater influence on the axial force. As for the exciting forces of the whole propeller, the cross flows have greater influence on the transverse and vertical forces, and if the cross flows in ship’s wake are not considered, the amplitudes of the main harmonics of transverse and vertical forces increase obviously.

Analysis of a Turbulent Propeller Inflow

2003 ◽  
Vol 125 (3) ◽  
pp. 533-542 ◽  
Author(s):  
Stephen A. Huyer ◽  
Stephen R. Snarski
Keyword(s):  
Boundary Layer ◽  
Velocity Field ◽  
Three Dimensional ◽  
Velocity Fields ◽  
Autocorrelation Analysis ◽  
Mean Velocity ◽  
Turbulent Inflow ◽  
Turbulent Flow Structure ◽  
Induced Velocity ◽  
Insight Into

The unsteady turbulent inflow into a swirl-inducing stator upstream of propeller (SISUP) propeller is presented. The upstream stators and hull boundary layer generate a complex, three-dimensional inflow that was measured using x-wire anemometry. High resolution measurements consisting of 12 locations in the radial direction and 600 in the circumferential direction yielded mean velocity and rms turbulent quantities for a total of 7200 points. The axial, radial, and circumferential velocity fields were thus measured. This enabled the induced velocity due to the stator wakes, the induced velocity due to the propeller, and the turbulent hull boundary layer to be characterized. To assist in decoupling the effects on the velocity field due to the stator and propeller, a potential flow computation of the swirl component was used. Spectra and autocorrelation analysis of the inflow velocity field were used to estimate the integral length scale and lend further insight into the turbulent flow structure. These data can be used to validate computational fluid dynamics codes and assist in developing of turbulent inflow models.

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

2018 ◽  
Vol 856 ◽  
pp. 531-551 ◽  
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.

PIV Measurements of the Cross-Flow Velocity Field in the Near Wake of a Generic Pickup Truck

2006 ◽  
Author(s):  
Bahram Khalighi
Keyword(s):  
Velocity Field ◽  
Symmetry Plane ◽  
Cross Flow ◽  
Velocity Data ◽  
Near Wake ◽  
Mean Velocity ◽  
Piv Measurements ◽  
Pickup Truck ◽  
The Mean ◽  
The Cross

The cross-flow field (flow in planes normal to the direction of motion) in the near wake of a generic pickup truck is investigated experimentally using Particle Image Velocimetry (PIV). The PIV measurements of the velocity field normal to the free-stream direction are carried out at four stream-wise locations behind the cab and the tailgate. The PIV data are processed to obtain the instantaneous velocity field, the mean and the turbulence properties of the flow. The instantaneous results in the near wake of the cab show various vortical structures. The mean velocity data shows that the flow moves from the sides toward the center of the bed near the tailgate. The velocity data in the near wake of the tailgate shows a pair of counter-rotating vortices that induces a downwash velocity field at the symmetry plane. This downwash promotes an attached flow behind the tailgate, thus generating a pressure recovery which leads to reductions in the total drag.

Investigation of Interstitial Velocity Field Inside Micro-Porous Media

2010 ◽  
Author(s):  
Debjyoti Sen ◽  
Mona Abdolrazaghi ◽  
David S. Nobes ◽  
Sushanta K. Mitra
Keyword(s):  
Porous Media ◽  
Velocity Field ◽  
Three Dimensional ◽  
Cross Flow ◽  
Flow Cell ◽  
Velocity Fields ◽  
Pore Region ◽  
Flow Recirculation ◽  
Two Component ◽  
Interstitial Velocity

An investigation of interstitial velocity field within a micro porous media is studied using a three component three dimensional (3C3D) μ-PIV system. The porous media is formed by packing of micro glass beads of size 400 μm inside a flow cell. The two component two dimensional (2C2D) velocity fields in micro pore region are obtained near the wall. 3C3D velocity field is obtained by scanning through 100 μm inside the porous media using the scanning μ-PIV system. Cross flow pattern and flow recirculation is observed within the micro pore region.

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

2007 ◽  
Author(s):  
Masashi Higashiura ◽  
Koichi Inose ◽  
Masahiro Motosuke ◽  
Shinji Honami
Keyword(s):  
Reynolds Number ◽  
Flow Visualization ◽  
Static Pressure ◽  
Low Reynolds Number ◽  
Velocity Ratio ◽  
Cross Flow ◽  
Vortex Pair ◽  
Synthetic Jet ◽  
The Cross ◽  
Low Reynolds

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.

Heat Transfer and Friction Augmentation in High Aspect Ratio, Ribbed Channels With Dissimilar Inlet Conditions

2010 ◽  
Author(s):  
Carson D. Slabaugh ◽  
Lucky V. Tran ◽  
J. S. Kapat ◽  
Bobby A. Warren
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Momentum Flux ◽  
Rectangular Channel ◽  
Cross Flow ◽  
Flux Ratio ◽  
Momentum Flux Ratio ◽  
The Cross ◽  
Inlet Conditions ◽  
Channel Configuration

This work is an investigation of the heat transfer and pressure-loss characteristics in a rectangular channel with ribs oriented perpendicular to the flow. The novelty of this study lies in the immoderate parameters of the channel geometry and transport enhancing features. Specifically, the aspect ratio (AR) of the rectangular channel is considerably high, varying from fifteen to thirty for the cases reported. Also varied is the rib-pitch to rib-height (p/e), studied at two values; 18.8 and 37.3. Rib-pitch to rib-width (p/w) is held to a value of two for all configurations. Channel Reynolds number is varied between approximately 3,000 and 27,000 for four different tests of each channel configuration. Each channel configuration is studied with two different inlet conditions. The baseline condition consists of a long entrance section leading to the entrance of the channel to provide a hydrodynamically-developed flow at the inlet. The second inlet condition studied consists of a cross-flow supply in a direction perpendicular to the channel axis, oriented in the direction of the channel width (the longer channel dimension). In the second case, the flow rate of the cross-flow supply is varied to understand the effects of a varying momentum flux ratio on the heat transfer and pressure-loss characteristics of the channel. Numerical simulations revealed a strong dependence of the local flow physics on the momentum flux ratio. The turning effect of the flow entering the channel from the cross-flow channel is strongly affected by the pressure gradient across the channel. Strong pressure fields have the ability to propagate farther into the cross-flow channel to ‘pull’ the flow, partially redirecting it before entering the channel and reducing the impingement effect of the flow on the back wall of the channel. Experimental result shows a maximum value of Nusselt number augmentation to be found in the 30:1 AR channel with the aggressive augmenter (p/e = 37.3) and a high momentum flux ratio: Nu/Nuo = 3.15. This design also yielded the friction with f/f0 = 2.6.

Combustion via multiple pairs of opposing premixed flames with a cross-flow

2016 ◽  
Vol 231 (1) ◽  
pp. 39-58 ◽  
Author(s):  
MM Kamal
Keyword(s):  
Momentum Flux ◽  
Cross Flow ◽  
Flux Ratio ◽  
Stability Limit ◽  
Injection Velocity ◽  
Nox Emissions ◽  
Stoichiometric Mixture ◽  
Lean Mixture ◽  
Momentum Flux Ratio ◽  
The Cross

A cylindrical burner accommodating stoichiometric fuel–air mixture combustion via multiple pairs of opposing jets and a cross-flow provided heat intensification and duplication of the stagnation impact for extending the firing limits and maximizing the power density. Six pairs of circumferentially opposing stoichiometric mixture jets sustained bulk injection velocities as high as 21.8 m/s and were associated with NOx emissions of 22 ppm, while emissions of 10 ppm were recorded upon reaching a lean limit equivalence ratio of 0.59. A stoichiometric mixture jet issuing perpendicular to the opposing jets at a momentum flux ratio of 0.3 increased the turbulence production rates to the extent that increased the maximum bulk injection velocity to 28.3 m/s and reduced the NOx emissions to 17 ppm. Since the recirculation zones between the two stagnation centers got compressed by increasing the momentum flux ratio to 0.8, the corresponding residence time reduction decreased the NOx emissions to 12 ppm. As the cross-flow mixture was made fuel–lean, dilution of the stoichiometric mixture by the fuel–lean mixture combustion products made it possible to get NOx emissions of single digit ppm. Emissions of 9 ppm resulted from using the cross-flow fuel–lean mixture jet due to compromising the flame stability limit extension and the temperature reduction in the post flame region. Such emissions, in turn, decreased to 4 ppm as the momentum flux ratio increased to 1.7 at which the stoichiometric mixture flames shrank into their ports. A minimum NOx emission index of 0.27 g/kg fuel was thus obtained at a volumetric heat release of 50.4 MW/m3. The momentum flux ratio corresponding to merging the two stagnation zones was correlated with Reynolds and Froude numbers, the jets’ separation as well as the density and viscosity values pertaining to the lean and stoichiometric mixtures’ flame temperatures.

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