Near-wall turbulent characteristics along very long thin circular cylinders

2011 ◽  
Vol 27 (3) ◽  
pp. 329-341 ◽  
Author(s):  
S.A. Jordan
Keyword(s):  
Circular Cylinders ◽  
Turbulent Characteristics ◽  
Near Wall

Algebraic Anisotropic Eddy Viscosity Model for Separated Flows of Internal Cooling Channels

2014 ◽  
Author(s):  
Weihong Li ◽  
Li Yang ◽  
Jing Ren ◽  
Hongde Jiang
Keyword(s):  
Heat Transfer ◽  
Eddy Viscosity ◽  
Separated Flows ◽  
Viscosity Model ◽  
Internal Cooling ◽  
Cooling Channels ◽  
Eddy Viscosity Model ◽  
Flow And Heat Transfer ◽  
Turbulent Characteristics ◽  
Near Wall

A new algebraic anisotropic eddy viscosity model (AEVM) is developed to account for the anisotropic characteristics of flow fields for internal cooling channels in a gas turbine. The model consist of two parts: k and ε near wall modeling are improved to obtain precise near wall turbulent characteristics and eddy viscosity; anisotropic ratios are derived to account for anisotropy and further modify the normal Reynolds stresses by combining implicit algebraic stress model and isotropic eddy viscosity model. The new algebraic anisotropic eddy viscosity model is validated in two cases: 1) flow prediction of backward facing step, better results are obtained especially turbulent quantities, 2) flow and heat transfer predictions of internal channels with ribs, numerical reattachment length after each rib is more close to the measured value after anisotropic modification, and heat transfer prediction accuracy is increased by 6–10%. Results indicate the present model can be applied to flow and heat transfer prediction of separated flows in internal cooling channels efficiently.

Influence of Inertial Particles on Turbulence Characteristics in Outer and Near Wall Flow as Revealed With High Resolution Particle Image Velocimetry

2016 ◽  
Vol 138 (9) ◽  
Author(s):  
Ammar Saber ◽  
T. Staffan Lundström ◽  
J. Gunnar I. Hellström
Keyword(s):  
Particle Image Velocimetry ◽  
Particle Image ◽  
Volume Fraction ◽  
Spherical Particles ◽  
Normal Velocity ◽  
Inertial Particles ◽  
Mean Flow ◽  
Turbulent Characteristics ◽  
Image Velocimetry ◽  
Near Wall

A fully developed turbulent particle-gas flow in a rectangular horizontal channel 100 × 10 × 4000 mm3 is disclosed with high spatial resolution two-dimensional (2D) particle image velocimetry (PIV). The objective is to increase the knowledge of the mechanisms behind alterations in turbulent characteristics when adding two sets of relatively large solid spherical particles with mean diameters of 525 and 755 μm and particle size distributions of 450–600 and 710–800 μm, respectively. Reynolds numbers are 4000 and 5600 and relatively high volume fraction of 5.4 × 10−4 and 8.0 × 10−4 are tested. Both the near wall turbulent boundary layer flow and outer core flow are considered. Results show that the carrier phase turbulent intensities increase with the volume fraction of the inertial particles. The overall mean flow velocity is affected when adding the particles but only to a minor extent. Near the wall, averaged velocity decreases while fluctuating velocity components increase when particles are added to the flow. Quadrant analysis shows the importance of sweep near the wall and ejection events in the region defined by y+ > 20. In conclusion, high inertia particles can enhance turbulence even at relatively low particle Reynolds number <90. In the near bottom wall region, particles tend to be a source of instability reflected as enhancement in rms values of the normal velocity component.

Influence of Wall Heating on Turbulent Structure

2007 ◽  
Author(s):  
Shivani T. Gajusingh ◽  
Kamran Siddiqui
Keyword(s):  
Flow Behavior ◽  
Streamwise Velocity ◽  
Wall Region ◽  
Turbulent Regime ◽  
Square Channel ◽  
Wall Heating ◽  
Turbulent Characteristics ◽  
The Mean ◽  
The Impact ◽  
Near Wall

An experimental study was conducted to investigate the impact of wall heating on the flow structure in the near-wall region inside a square channel. PIV was used to measure the two-dimensional velocity fields. The measurements were conducted for a range of mass flow rates that cover laminar and turbulent regimes. The results have shown that when a flow is unstably stratified via heating through a bottom wall, both the mean and turbulent characteristics are affected. The results have shown that the impact of wall heating on the flow behavior is significantly different for laminar and turbulent flow regimes. It was found that when a flow that is originally laminar is heated, the mean streamwise velocity in the near-wall region is significantly increased and turbulence is generated in the flow predominantly due to buoyancy. When the flow is in the turbulent regime, addition of heat reduces the magnitudes of mean streamwise velocity and turbulent properties. The reduction in the magnitudes of turbulent properties in this flow regime is due to the working of turbulence against the buoyancy forces.

scholarly journals PIV investigation of cavitating flows around circular cylinders with hydrophobic coatings

2021 ◽  
Vol 1 (1) ◽  
Author(s):  
Konstantin Dobroselsky ◽  
Anatoliy Lebedev ◽  
Alexey Safonov ◽  
Sergey Starinskiy ◽  
Vladimir Dulin
Keyword(s):  
Test Section ◽  
Pressure Sensors ◽  
Circular Cylinders ◽  
Bulk Velocity ◽  
Water Tunnel ◽  
Slip Effect ◽  
Long Distance ◽  
Hydrophobic Coatings ◽  
Heating Section ◽  
Near Wall

The treatment of the hydrophobic properties of solid surfaces is considered as a passive method to reduce the drag in water flows (Rothstein, 2010) and to potentially affect the flow separation and vortex shedding (Sooraj et al., 2020). The manufacturing of surfaces with micro- and nano-scale roughness allows to extend the hydrophobicity towards superhydrophobicity with the contact angle close to 180°. In such conditions the solid surface is not wetted completely and the air-water interphase partially remains on the surface texture. This results in so-called flow slip effect. Therefore, a local phase transition during the flow cavitation or gas effervescence in near-wall low-pressure regions may additionally affect the slip effect for hydrophobic surfaces. The present work is focused on the comparison between cavitating and noncavitating flows around circular cylinders with lateral sectors with hydrophobic and non-hydrophobic coatings. The experiments are performed in a water tunnel, which consists of a water outgassing and cooling/heating section, honeycomb, contraction section, test section and diffuser. The water flow is driven by an electric pump, providing a bulk velocity up to 10 m/s in the transparent test section with 1 m length and 80×150 mm2 rectangular cross-section. The facility is equipped with an ultrasonic flowmeter, temperature and pressure sensors. Besides, the static pressure inside the water tunnel can be varied by using a special shaft section. The measurements are performed by using high-repetition and low-repetition PIV systems. The former is used for the analysis of large-scale flow dynamics in the wake region, whereas the latter one is used for high-resolution measurements in near-wall regions by using a long-distance microscope. The Reynolds number based on the bulk velocity of the flow, diameter of the cylinders (D = 26 mm) and kinematic viscosity of the water is varied up to 2×105..

NEAR-WALL CHARACTERISTICS OF AN IMPINGING GASOLINE SPRAY AT INCREASED AMBIENT PRESSURE AND WALL TEMPERATURE

2009 ◽  
Vol 19 (11) ◽  
pp. 997-1012 ◽  
Author(s):  
Jochen Stratmann ◽  
D. Martin ◽  
P. Unterlechner ◽  
R. Kneer
Keyword(s):  
Wall Temperature ◽  
Ambient Pressure ◽  
Near Wall

Turbulent Characteristics of Curved Wall Jets

1998 ◽  
Vol 29 (4-5) ◽  
pp. 218-224
Author(s):  
A. A. Khalatov ◽  
T. A. Zheleznaya ◽  
I. A. Izgoreva
Keyword(s):  
Wall Jets ◽  
Turbulent Characteristics

Nonisothermal Mixing of a Near-Wall Gas-Liquid Jet with a Flow in a Tube

2001 ◽  
Vol 32 (4-6) ◽  
pp. 7
Author(s):  
Viktor I. Terekhov ◽  
K. A. Sharov ◽  
N. E. Shishkin ◽  
V. P. Lebedev
Keyword(s):  
Liquid Jet ◽  
Near Wall
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