Begell House Inc.
International Journal of Fluid Mechanics Research
FMR
2152-5102
44
2
2017
THREE-DIMENSIONAL INSTABILITY OF NON-NEWTONIAN VISCOELASTIC LIQUID JETS ISSUED INTO A STREAMING VISCOUS (OR INVISCID) GAS
93-113
Mohamed F.
El-Sayed
Department of Mathematics, Faculty of Education, Ain Shams University, Heliopolis (Roxy), Cairo, Egypt; Department of Mathematics, College of Science, Qassim University, P. O. Box 6644, Buraidah 51452, Saudi Arabia
G. M.
Moatimid
Department of Mathematics, Faculty of Education, Ain Shams University, Heliopolis, Roxy, Cairo, Egypt
F. M. F.
Elsabaa
Department of Mathematics, Faculty of Education, Ain Shams University, Heliopolis, Roxy 11757, Cairo, Egypt
M. F. E.
Amer
Department of Mathematics, Faculty of Education, Ain Shams University, Heliopolis, Roxy 11757, Cairo, Egypt
A linear stability analysis is presented for a Rivlin-Ericksen viscoelastic liquid jet moving in a streaming viscous (or inviscid) gas medium with three-dimensional disturbances. The dispersion relation between the nondimensional growth rate and nondimensional wave number is derived using appropriate boundary conditions, and it is solved numerically via a new technique using Mathematica software. The effects of different parameters on the stability behavior of the system are discussed in detail. It is shown that a viscoelastic liquid jet streaming in a viscous gas is more unstable than that in an inviscid one, and less unstable than the corresponding case of a viscous liquid jet. It is shown also that the Weber number, Raynolds number, liquid velocity, gas density, gas-to-liquid density ratio, and the gas-to-liquid viscosity ratio have destabilizing effects on the system, while the viscoelasticity parameter and surface tension have usually stabilizing influences. The Ohnesorge number and gas-to-liquid velocity ratio are found to have dual roles on the stability of the system. Finally, comparisons between the cases of ambient viscous and inviscid gases as well as the cases of symmetric and antisymmetric disturbances are examined in detail.
ANALYSIS OF TRANSVERSE VIBRATIONAL RESPONSE AND INSTABILITIES OF AXIALLY MOVING CNT CONVEYING FLUID
115-129
Soheil
Oveissi
Department of Mechanical Engineering, Najafabad Branch, Islamic Azad University, Najafabad, Iran
Davood Semiromi
Toghraie
Department of Mechanical Engineering, Khomeinishahr Branch, Islamic Azad University,
Khomeinishahr, Iran
S. Ali
Eftekhari
Department of Mechanical Engineering, Khomeinishahr Branch, Islamic Azad University,
Khomeinishahr, Iran
The transverse vibration and instability of the axially moving carbon nanotube (CNT) conveying fluid were studied.
To this end, the nonlocal continuum theory and Knudsen number were utilized to consider the small-scale effect of the nanostructure and nanoflow, respectively. The Hamilton's principle was employed to obtain the governing equation of
motion for the axially moving CNT with and without fluid passing through it, and the analysis was carried out using
the Galerkin weighted residual method. In addition, to consider the small-size effect of nanoflow through the CNT, the Knudsen number is introduced. The results indicate that the resonant frequencies in which the instabilities emerge
can be influenced by the fluid flow passing through the CNT more than the axially traveling CNT speed. In addition,
it can be observed that the axially moving CNT conveying fluid, while the axially CNT velocity is constant, is more
stable. This demonstrates, however, that the stationary CNT conveying fluid is more stable than all cases of the axially
moving CNT conveying fluid.
ELUCIDATION OF LONGITUDINALLY GROOVED-RIBLETS DRAG REDUCTION PERFORMANCE USING PRESSURE DROP MEASUREMENTS
131-153
Hayder A.
Abdulbari
Faculty of Chemical and Natural Resources Engineering, Universiti Malaysia Pahang,
Gambang 26300, Kuantan, Pahang, Malaysia; Center of Excellence for Advanced Research in Fluid Flow, Universiti Malaysia Pahang,
Gambang 26300, Kuantan, Pahang, Malaysia
Hassan D.
Mahammed
Faculty of Chemical and Natural Resources Engineering, Universiti Malaysia Pahang,
Gambang 26300, Kuantan, Pahang, Malaysia
Zulkefli B.
Yaacob
Faculty of Chemical and Natural Resources Engineering, Universiti Malaysia Pahang,
Gambang 26300, Kuantan, Pahang, Malaysia
Wafaa K.
Mahmood
Department of Production Engineering and Metallurgy, University of Technology, Baghdad,
IRAQ
The need to determine affordable and environmentally friendly methods of reducing skin friction can be identified as one of the reasons contributing towards the study of the effectiveness of riblet shapes. Water tank experiments were
carried out to optimize the shape and dimensions of microstructure grooves over a flat plate. The use of organized microstructures on channel walls is proposed to obtain lower values of pressure losses on smooth walls. Three shapes of microstructure grooves were investigated, with same groove height (600 μ;m) and five spacing dimensions (600, 750, 1000, 1500 μ;m), in water flows with velocities of up to 0.4 m/s. This was done for all selected types of riblet, which are fixed with the direction aligned with the flow. The experimental results showed that the size and shape of the riblets can massively incubate some of the turbulent structures formed on the surface and that will lead to a more controllable flow environment, which can result in drag reduction.
CFD ANALYSIS OF FLOW PATTERN INSIDE A MACH 3 BLOWDOWN SUPERSONIC WIND TUNNEL ON START-UP AND STEADY STATE OPERATION CONDITIONS
155-168
Mehrdad
Rabani
Department of Mechanical Engineering, Yazd University,Yazd, Iran
Mojtaba Dehghan
Manshadi
Mechanical and Aerospace Engineering Department, Malek-Ashtar, University of Technology, Esfahan, Iran
Ramin
Rabani
Department of Mechanical Engineering, Yazd University,Yazd, Iran
The time accurate numerical simulation of transient shock behavior and flow-field analysis in a Mach 3 blowdown
supersonic wind tunnel was carried out. For this purpose, the shape of the Mach contour for the given Mach number
was determined using the method of characteristics and the numerical solutions were obtained using the finite volume
method. The numerical method was validated by the previous numerical study involving flow in a double throat nozzle,
and the results showed close behavior with each other. The impact of different stagnation temperature on the flow-field
characteristics was investigated, and the results indicated that although the increase of stagnation temperature to 700 K increases the static temperature in the test section by ~150 K, drying the working fluid can be a more effective solution in preventing the condensation of fluid flow in the test section.
TURBULENT WAKES BEHIND BED-MOUNTED HEMISPHERES IN CO-EXISTING SURFACE WAVE
169-183
Krishnendu
Barman
Assistant Professor
Koustuv
Debnath
Department of Aerospace Engineering and Applied Mechanics, Indian Institute of Engineering
Science and Technology, Shibpur 603203, India
The objective of this research is to examine the turbulent flow characteristics at the wake region of artificial single
and dual hemispheres fixed to the bottom wall of an open channel under wave and current interaction. The effect
of surface wave on the mean velocity, turbulence intensities, and Reynolds shear stress profiles over hemispherical obstacles has been presented in this paper. All three velocity components with fluctuations were measured using 3D micro-acoustic Doppler velocimeter. The study was carried out at the submergence ratio, h/h' = 7.1 where h = flow depth and h' = obstacle height and three different wave frequencies f = 0.5, 1, and 2 Hz, respectively. On the basis of quadrant analysis, the contribution of stress fractions to the Reynolds shear stress corresponding to each quadrant event at the wake region of hemispheres is presented to evaluate the turbulent bursting events. Furthermore, the power spectral density for the velocity fluctuation was analyzed to evaluate the distribution of energy at the different scales of
fluctuation.