Simultaneous measurement of unsteady flow and thermal fields in a turbulent channel flow with dynamic PIV and high-speed infrared thermography

2016 ◽  
Vol 2016 (0) ◽  
pp. H134
Author(s):  
Shnuske Yamada ◽  
Hjime Nakamura
Keyword(s):  
Unsteady Flow ◽  
Infrared Thermography ◽  
Channel Flow ◽  
Simultaneous Measurement ◽  
High Speed ◽  
Turbulent Channel Flow ◽  
Thermal Fields ◽  
Dynamic Piv

scholarly journals Turbulent channel flow over an anisotropic porous wall – drag increase and reduction

2018 ◽  
Vol 842 ◽  
pp. 381-394 ◽  
Author(s):  
Marco E. Rosti ◽  
Luca Brandt ◽  
Alfredo Pinelli
Keyword(s):  
Drag Reduction ◽  
Channel Flow ◽  
High Speed ◽  
Vertical Direction ◽  
Porous Wall ◽  
Turbulent Channel Flow ◽  
Spanwise Direction ◽  
Normal Velocity ◽  
Porous Walls ◽  
The One

The effect of the variations of the permeability tensor on the close-to-the-wall behaviour of a turbulent channel flow bounded by porous walls is explored using a set of direct numerical simulations. It is found that the total drag can be either reduced or increased by more than 20 % by adjusting the permeability directional properties. Drag reduction is achieved for the case of materials with permeability in the vertical direction lower than the one in the wall-parallel planes. This configuration limits the wall-normal velocity at the interface while promoting an increase of the tangential slip velocity leading to an almost ‘one-component’ turbulence where the low- and high-speed streak coherence is strongly enhanced. On the other hand, strong drag increase is found when high wall-normal and low wall-parallel permeabilities are prescribed. In this condition, the enhancement of the wall-normal fluctuations due to the reduced wall-blocking effect triggers the onset of structures which are strongly correlated in the spanwise direction, a phenomenon observed by other authors in flows over isotropic porous layers or over ribletted walls with large protrusion heights. The use of anisotropic porous walls for drag reduction is particularly attractive since equal gains can be achieved at different Reynolds numbers by rescaling the magnitude of the permeability only.

Mixing of two thermal fields emitted from line sources in turbulent channel flow

2008 ◽  
Vol 609 ◽  
pp. 349-375 ◽  
Author(s):  
E. COSTA-PATRY ◽  
L. MYDLARSKI
Keyword(s):  
Correlation Coefficient ◽  
Channel Flow ◽  
Large Scale ◽  
Turbulent Channel Flow ◽  
Separation Distance ◽  
Wall Region ◽  
Thermal Plume ◽  
Passive Scalars ◽  
Thermal Fields ◽  
Fast Evolution

The interaction of two passive scalars (both temperature in air) emitted from concentrated line sources in fully developed high-aspect-ratio turbulent channel flow is studied. The thermal fields are measured using cold-wire thermometry in a flow with a Reynolds number (Uh/ν) of 10200.The transverse total root-mean-square (RMS) temperature profiles are a function of the separation distance between the line sources (d/h), their average wall-normal position (ysav/h), and the downstream location (x/h), measured relative to the line sources. Similarly, profiles of the non-dimensional form of the scalar covariance, the correlation coefficient (ρ), are a function of the same parameters and quantify the mixing of the two scalars.The transverse profiles of the correlation coefficient are generally largest at the edges of the thermal plume and smallest in its core. When the line sources are not symmetrically located about the channel centreline, the minimum in the correlation coefficient transverse profiles drifts towards the (closer) channel wall. For source locations that are equidistant from the channel centreline, the minimum correlation coefficient occurs at the centreline, due to the underlying symmetry of this geometry. The initial downstream evolution of the correlation coefficient depends significantly on d/h, similar to that in homogeneous turbulence. However, there is always a dependence on ysav/h, which increases in importance as both the downstream distance is increased and the wall is approached. Lastly, the correlation coefficient profiles tend towards positive values in the limit of large downstream distances (relative to the source separation), though further measurements farther downstream are required to confirm the exact value(s) of their asymptotic limit(s).Spectral analysis of the cospectra and coherency spectra indicates that the large scales evolve more rapidly than the small ones. Furthermore, the fast evolution of the large scales was most evident when the sources were located close to the wall. This presumably derives from the large-scale nature of turbulence production, which is strong in the near-wall region.

Unsteady Flow Structure Behind a Heated Cylinder Measured by Time-Resolved PIV With Thermocouple Sensing

2011 ◽  
Author(s):  
Yuji Ohta ◽  
Takuya Mukoyama ◽  
Koichi Hishida
Keyword(s):  
Unsteady Flow ◽  
Turbulent Flows ◽  
Simultaneous Measurement ◽  
High Speed ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Wake Region ◽  
Time Resolved ◽  
Heated Cylinder ◽  
Thermal Fluid Flow

This paper deals with a technique for time-resolved simultaneous measurement of velocity and temperature in wake region. A measurement technique, combining a high-speed particle image velocimetry (PIV, 1000 frame per second) with thermo-couple sensing (T-type, 50μm), has been developed for acquiring time-resolved two-dimensional velocity and temperature data in thermal-fluid flow, simultaneously. To accomplish the simultaneous measurement, thermocouple time constant was compensated by solving inverse problem with experimental time-resolved velocity data. The technique was applied to a wake region behind a heated circular cylinder in steady and unsteady flow. The evolutions of vortical and thermal structures were obtained in order to examine the mechanism of the turbulent heat transfer in such turbulent flows.

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