Large scale hair-pin vortices from a pair of surface mounted hemispherical spheres at a low Reynolds number

2013 ◽  
Author(s):  
CC Chen ◽  
Jung-Hua Chou ◽  
CC Hsu
Keyword(s):  
Reynolds Number ◽  
Large Scale ◽  
Low Reynolds Number ◽  
Low Reynolds

Effect of Large Scale 3-D Structures on the Flow Around a Heated Cylinder at Low Reynolds Number

2018 ◽  
Vol 101 (2) ◽  
pp. 553-577 ◽  
Author(s):  
Stefano Rolfo ◽  
Konstantinos Kopsidas ◽  
Shahnurriman A. Rahman ◽  
Charles Moulinec ◽  
David R. Emerson
Keyword(s):  
Reynolds Number ◽  
Large Scale ◽  
Low Reynolds Number ◽  
Heated Cylinder ◽  
Low Reynolds

Numerical Design and Study of a MEMS-Based Micro Turbine

2005 ◽  
Author(s):  
Tatsuo Onishi ◽  
Ste´phane Burguburu ◽  
Olivier Dessornes ◽  
Yves Ribaud
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Skin Friction ◽  
Large Scale ◽  
Low Reynolds Number ◽  
Turbine Blades ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Low Reynolds ◽  
Micro Turbine

A full three dimensional Navier-Stokes solver elsA developed by ONERA is used to design and study the aerothermodynamics of a MEMS-based micro turbine. This work is performed in the framework of micro turbomachinery project at ONERA. A few millimeter scale micro turbine is operated in a low Reynolds number regime (Re = 5,000∼50,000), which implies a more important influence of skin friction and heat transfer than the conventional large-scale gas turbine. The 2D geometry constraints due to the limitation of fabrication technology also distinguish the aerothermodynamic characteristics of a micro turbine from that of conventional turbomachinery. Thus, for the foundation of aerothermodynamic design of micro turbomachinery, understanding of low Reynolds number effects on the performance is required and then the design of the turbine geometry can be optimized. In this study, aero-thermodynamic effects at low Reynolds number and different stator/rotor configurations are examined with a prescribed wall temperature. Losses due to heat transfer to walls and skin friction are estimated and their effects on the operating performance are discussed. Power delivery to turbine blades is checked and found satisfactory to give the objective design value of more than 100W. The effects of turbine exhaust geometry and the number of blades on turbine performance are also discussed.

Very-large-scale fluctuations in turbulent channel flow at low Reynolds number

2016 ◽  
Vol 62 ◽  
pp. 593-597
Author(s):  
Masaharu Matsubara ◽  
Shun Horii ◽  
Yoshiyuki Sagawa ◽  
Yuta Takahashi ◽  
Daisuke Saito
Keyword(s):  
Reynolds Number ◽  
Channel Flow ◽  
Large Scale ◽  
Low Reynolds Number ◽  
Turbulent Channel Flow ◽  
Low Reynolds

Separation-Bubble-Transition Measurements on a Low-Re Airfoil Using Particle Image Velocimetry

2005 ◽  
Author(s):  
B. R. McAuliffe ◽  
M. I. Yaras
Keyword(s):  
Reynolds Number ◽  
Particle Image Velocimetry ◽  
Large Scale ◽  
Particle Image ◽  
Reverse Flow ◽  
Separation Bubble ◽  
Low Reynolds Number ◽  
Piv Measurements ◽  
Image Velocimetry ◽  
Low Reynolds

This paper presents experimental results on separation-bubble transition at low Reynolds number and low freestream turbulence, measured on an airfoil using particle image velocimetry (PIV). The two-dimensional PIV measurements have been performed over the suction surface of a low-Reynolds-number airfoil in a water tow-tank facility. Reynolds numbers, based on airfoil chord length and towing speed, of 40,000 and 65,000 have been examined at various angles of incidence, providing a range of streamwise pressure distributions and transitional separation-bubble geometries. The types of bubbles observed range from a short and thick bubble with separation near the leading edge of the airfoil, to a long and thin bubble with separation far downstream of the suction peak. The PIV measurements facilitate visualization of the vortex dynamics associated with separation-bubble transition. The growth of instability waves within the separated shear layer and eventual breakdown into turbulence is documented through the instantaneous vector fields. For all cases examined, large-scale vortex shedding and multiple reverse-flow zones are observed in the reattachment region. A technique for estimating the location of transition onset based on statistical turbulence quantities is presented, and comparisons are made to existing transition models.

Experiments on the instability waves in a supersonic jet and their acoustic radiation

1975 ◽  
Vol 69 (1) ◽  
pp. 73-95 ◽  
Author(s):  
Dennis K. Mclaughlin ◽  
Gerald L. Morrison ◽  
Timothy R. Troutt
Keyword(s):  
Reynolds Number ◽  
High Reynolds Number ◽  
Large Scale ◽  
Acoustic Radiation ◽  
Low Reynolds Number ◽  
Supersonic Jet ◽  
Hot Wire ◽  
Theoretical Predictions ◽  
Low Reynolds ◽  
High Reynolds

An experimental investigation of the instability and the acoustic radiation of the low Reynolds number axisymmetric supersonic jet has been performed. Hot-wire measurements in the flow field and microphone measurements in the acoustic field were obtained from different size jets at Mach numbers of about 2. The Reynolds number ranged from 8000 to 107000, which contrasts with a Reynolds number of 1·3 × 106for similar jets exhausting into atmospheric pressure.Hot-wire measurements indicate that the instability process in the perfectly expanded jet consists of numerous discrete frequency modes around a Strouhal number of 0·18. The waves grow almost exponentially and propagate downstream at a supersonic velocity with respect to the surrounding air. Measurements of the wavelength and wave speed of theSt= 0·18 oscillation agree closely with Tam's theoretical predictions.Microphone measurements have shown that the wavelength, wave orientation and frequency of the acoustic radiation generated by the dominant instability agree with the Mach wave concept. The sound pressure levels measured in the low Reynolds number jet extrapolate to values approaching the noise levels measured by other experimenters in high Reynolds number jets. These measurements provide more evidence that the dominant noise generation mechanism in high Reynolds number jets is the large-scale instability.

Radiofrequency plasma stabilization of a low-Reynolds-number channel flow

2014 ◽  
Vol 748 ◽  
pp. 663-691 ◽  
Author(s):  
Timothy J. Fuller ◽  
Andrea G. Hsu ◽  
Rodrigo Sanchez-Gonzalez ◽  
Jacob C. Dean ◽  
Simon W. North ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Channel Flow ◽  
Large Scale ◽  
Reynolds Shear Stress ◽  
Low Reynolds Number ◽  
Plasma Heating ◽  
Shear Stresses ◽  
Exponential Factor ◽  
Turbulence Decay ◽  
Low Reynolds

AbstractThe effects of plasma heating and thermal non-equilibrium on the statistical properties of a low-Reynolds-number ($Re_{\tau } = 49$) turbulent channel flow were experimentally quantified using particle image velocimetry, two-line planar laser-induced fluorescence, coherent anti-Stokes Raman spectroscopy and emission spectroscopy. Tests were conducted at two radiofrequency plasma settings. The nitrogen, in air, was vibrationally excited to $T_{vib} \sim 1240\ \mathrm{K}$ and 1550 K for 150 W and 300 W plasma settings, respectively, while the vibrational temperature of the oxygen and the rotational/translational temperatures of all species remained near room temperature. The peak axial turbulence intensities in the shear layers were reduced by 15 and 30 % in moving across the plasma for the 150 and 300 W cases, respectively. The plasma did not alter the transverse intensities. The Reynolds shear stresses were reduced by 30 and 50 % for the 150 and 300 W cases. The corresponding Reynolds shear stress correlation coefficient was also reduced, which indicates that the large-scale structures were diminished. Finally, the plasma enhanced the turbulence decay in the zero-shear regions, where the power law decay $t^{-1/n}$ exponential factor $n$ decreased from 1.0 to 0.8.

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