Begell House Inc.
Journal of Flow Visualization and Image Processing
JFV
1065-3090
26
2
2019
PIV STUDY OF RADIAL WALL JET FORMED BY A NORMALLY IMPINGING TURBULENT SYNTHETIC JET
99-126
10.1615/JFlowVisImageProc.2019029526
Udaysinh S.
Bhapkar
Department of Mechanical Engineering, Indian Institute of Technology, Bombay, Mumbai, 400076, India
Harekrishna
Yadav
Department of Mechanical Engineering, Indian Institute of Technology Bombay,
Powai, Mumbai 400076, India
Amit
Agrawal
Department of Mechanical Engineering, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India
synthetic jet
radial wall jet
particle image velocimetry
confinement
In this work, the flow field measurement of turbulent synthetic jet is undertaken using particle image velocimetry (PIV). The measurements are performed with the aim of understanding the basic fluid flow processes in the wall region of an impinging synthetic jet and of better understanding the heat transfer processes involved in such flows. The study has been performed at a Reynolds number of 5588, Strouhal number of 0.165, and Stokes number of 75 for three different orifice-to-wall distances (z/d = 1, 3, and 8, where d is the orifice diameter). The locations have been chosen because the heat transfer characteristics of synthetic jet and its behavior are different at these axial locations. The instantaneous flow fields of impinging jet show the strong impact of vortices on the ensuing flow and behave differently for different surface spacings near the stagnation region and in the wall jet region. Formation of a large recirculation region is noted at a lower axial distance of z/d = 1, where the effect of confinement is particularly large compared to other surface spacings. A detailed quantitative analysis of mean and RMS velocity profiles has also been undertaken in the study. It is observed that beyond the radial location (r) of 2.5d, the boundary layer thickness grows linearly. The variation of mass flow rate with r can be described by the power law r0.49. The PIV measurements further show that the nature of axial velocity profiles changes with axial distance. At an axial distance of z/d = 3, two axisymmetric secondary peaks are observed but at the higher axial distance of z/d = 8 such secondary peaks are absent. The flow is found to be reasonably isotropic in both the near-stagnation and self-similar regimes. These detailed observations are important for better understanding of heat transfer from impinging synthetic jets.
FLOW ANALYSIS OF THE IMPINGEMENT OF A VARIABLE-DIAMETER SYNTHETIC JET
127-148
10.1615/JFlowVisImageProc.2019029368
Alexander J.
Zielinski
Washington State University, Vancouver, WA 98686, USA
Stephen A.
Solovitz
Washington State University Vancouver, 14204 NE Salmon Creek Ave., Vancouver, WA, USA 98686
synthetic jet
impingement cooling
variable diameter
particle image velocimetry
Synthetic jets have been used for impingement heat transfer in compact electronics cooling. A novel form of synthetic jet uses a time-varying diameter, which can produce increased momentum flow and heat transfer when compared to fixed-diameter devices with the same average size, De. This benefit was most significant over an axial range relatively close to the exit, corresponding to nondimensional positions, x/De, from 1 to 3. Particle image velocimetry (PIV) was applied to examine the flow mechanisms behind this behavior, using both time-averaged and phase-averaged analysis. In the time average, the variable-diameter jet produces a concentrated jet with more significant entrainment, exceeding its fixed-diameter counterpart by a factor of nearly four. Over the actuation cycle, phase-averaged flow fields display a larger, more concentrated vortex ring, which increases the maximum speed, vorticity, and circulation. The vortex ring travels across the impingement distance nearly twice as fast with a variable diameter, though, so it only has an effect during a brief portion of the actuation cycle. This indicates that the device position must be selected carefully, as its benefits will be most significant when placed close to the target.
EFFECT OF TRIANGULAR MICROGROOVES ON DRAG REDUCTION IN RECTANGULAR PIPE FLOW
149-167
10.1615/JFlowVisImageProc.2019028998
Entian
Li
Jiangsu Key Laboratory of Oil and Gas Storage and Transportation Technology, Changzhou
University, Changzhou, Jiangsu, PR China
Yang
Liu
School of Petroleum Engineering, Changzhou University, Changzhou 213164,
PR China
Pei
Yao
Department of Chemistry and Materials Engineering, Changzhou Vocational
Institute of Engineering, Changzhou, 213164, PR China
Xiang
Hu
School of Petroleum Engineering, Changzhou University, Changzhou 213164,
PR China
Lianghui
Guo
School of Petroleum Engineering, Changzhou University, Changzhou 213164,
PR China
Wen
Liu
School of Petroleum Engineering, Changzhou University, Changzhou 213164,
PR China
drag reduction
turbulence
flow control
flow visualization
microstructures
particle image velocimetry
It has been known for decades that turbulent flow may benefit greatly from drag reduction provided by microgrooves. The original inspiration came from mimicking the surface microstructures of the skin of fast swimming sharks. For the great potential benefit of application in long-distance pipeline transportation of oil or tap water, streamwise-aligned microgrooves are used in a rectangular pipe flow in this study. A detailed experimental system is discussed and the microgroove geometries are defined. Pressure drop collected using different h/s ratio microgrooves of microgrooved surfaces fabricated for the flow cell is provided and the drag reduction rate is analyzed and compared to the results of previous researches. To explore the mechanism of drag reduction of microgrooves, a visualization test by a particle image velocimetry (PIV) is conducted, and the detailed flow field, including the instantaneous mean velocity, Reynolds shear stress, turbulent intensities, and the vorticity is presented and discussed. Moreover, the drag reduction mechanism of microgrooves is proposed and discussed.
PARTIAL DIFFERENTIAL EQUATION-BASED SHARPENING ALGORITHM FOR IMAGES TAKEN IN FOGGY ENVIRONMENT
169-183
10.1615/JFlowVisImageProc.2019030309
Min
Qiu
Public Mathematics Department, School of Sciences, Hubei University of Automotive Technology, No. 167, Checheng West Road, Shiyan, Hubei 442002, China
fractional order
partial differential equation
defogging algorithm
atmospheric scattering model
Images taken in natural environment will have information loss, i.e., image blurring, limited by the shooting technology and equipment. Especially in foggy weather, image blurring is more serious, which has a negative impact on some fields which requires certain clarity of images. In order to make images taken in foggy weather clearer, image enhancement algorithm of fractional partial differential equation model was used and the defogging and enhancement processing was carried out on images taken in foggy environment on MATLAB in this study. Moreover, it was compared with the dark channel prior algorithm and the integer order partial differential equation model algorithm. The results showed that the three algorithms could effectively remove most of the fog. The comparison of the processed images and the average gradient, peak signal-to-noise ratio and information entropy of the images suggested that the fractional partial differential equation algorithm had the best defogging and enhancement performance, but it took more time in processing images than the other two algorithms.
ITERATIVE METHOD TO ANALYZE THE FLOW BEHAVIOR AROUND SUPERCAVITATING HYDROFOIL
185-207
10.1615/JFlowVisImageProc.2019030191
Adjali
Saadia
Laboratoire d'Aéro-Hydrodynamique Naval, Département de Génie Maritime,
Université des Sciences et de la Technologie d'Oran Mohamed Boudiaf,
USTO-MB, Oran, Algérie
Tayeb
Yahiaoui
Laboratoire d'Aéronautique et Systèmes Propulsifs, Département de Génie Mécanique,
Université des Sciences et de la Technologie d’Oran Mohamed Boudiaf, USTO-MB, Oran,
Algérie
Belkadi
Mustapha
Laboratoire d'Aéro-Hydrodynamique Naval, Département de Génie Maritime,
Université des Sciences et de la Technologie d'Oran Mohamed Boudiaf,
USTO-MB, Oran, Algérie
Jean Marc
Laurens
Brest University, ENSTA Bretagne, 2 Rue Francois Verny, 29806 Brest, Cedex
9 la France
breaking waves
cavitation
free surface
hydrofoil
VOF
In this article, we present the results of numerical simulations of 2D NACA profiles advancing at constant velocities close to the free surface. First, we use a NACA0012 hydrofoil section and compare our results with those of the famous Duncan experiment in order to validate our simulation methodology. Then, a NACA0015 hydrofoil was used at different immersion depths. We confirm that the lift increases as we approach the free surface until breaking waves were generated. Then we perform flow simulations in the presence of sheet cavitation at the suction side of the profile with a different number of cavitations. After that, using an iterative procedure, we combine the free surface and sheet cavitation effects on the NACA16-006 hydrofoil for different cavitation numbers at the critical depth. Finally a supercavitating foil is tested with our procedure. As expected, the lift increases as the cavitation number is decreasing.