Simultaneous Measurements of Unsteady Thermal and Flow Fluctuations Using High-Speed Infrared Thermography and PIV Over a Backward Facing Step

2017 ◽  
Author(s):  
Shunsuke Yamada ◽  
Hajime Nakamura
Keyword(s):  
Heat Transfer ◽  
Infrared Thermography ◽  
Vortex Structure ◽  
High Speed ◽  
Stereoscopic Particle Image Velocimetry ◽  
Heated Wall ◽  
Wall Region ◽  
Backward Facing Step ◽  
Combined System ◽  
Near Wall

In order to investigate the flow and heat transfer fluctuations in the near-wall region downstream a backward facing step, a Time-resolved Stereoscopic Particle Image Velocimetry (TS-PIV) and a high-speed infrared thermography (IRT) combined system was constructed. Using this measurement system, the time series of the velocity in the vicinity of the heated wall and the heat transfer on the heated wall were measured at Reynolds number, which is based on the step height and inlet mainstream velocity, of 2.5 × 103. It confirmed the validity of the velocity fluctuation obtained by using TS-PIV. The results showed that the forward and downwash flows correspond to the enhancement of the heat transfer in the near-wall region. Also, the vortex structure in the yz plane was detected by Qyz-criterion, and the locational relationship between the vortex structure and the heat transfer enhancement was investigated.

Large-eddy simulation of the turbulent flow through a heated square duct

2002 ◽  
Vol 453 ◽  
pp. 201-238 ◽  
Author(s):  
M. SALINAS VÁZQUEZ ◽  
O. MÉTAIS
Keyword(s):  
High Speed ◽  
Secondary Flows ◽  
Heated Wall ◽  
Wall Region ◽  
Central Plane ◽  
Square Duct ◽  
Low Speed ◽  
Size Limitation ◽  
Large Eddy ◽  
Near Wall

Large-eddy simulations of a compressible turbulent square duct flow at low Mach number are described. First, we consider the isothermal case with all the walls at the same temperature: good agreement with previous incompressible DNS and LES results is obtained both for the statistical quantities and for the turbulent structures. A heated duct with a higher temperature prescribed at one wall is then considered and the intensity of the heating is varied widely. The increase of the viscosity with temperature in the vicinity of the heated wall turns out to play a major rôle. We observe an amplification of the near-wall secondary flows, a decrease of the turbulent fluctuations in the near-wall region and, conversely, their enhancement in the outer wall region. The increase of the viscous thickness with heating implies a significant augmentation of the size of the characteristic flow structures such as the low- and high-speed streaks, the ejections and the quasi-longitudinal vorticity structures. For strong enough heating, the size limitation imposed by the lateral walls leads to a single low-speed streak located near the duct central plane surrounded by two high-speed streaks on both sides. Violent ejections of slow and hot fluid from the heated wall are observed, linked with the central low-speed streak. A selective statistical sampling of the most violent ejection events reveals that the entrainment of cold fluid, originated from the duct core, at the base of the ejection and its subsequent expansion amplifies the ejection intensity.

Direct numerical simulation of turbulent flow and heat transfer in a spatially developing turbulent boundary layer laden with particles

2018 ◽  
Vol 845 ◽  
pp. 417-461 ◽  
Author(s):  
Dong Li ◽  
Kun Luo ◽  
Jianren Fan
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Turbulent Flow ◽  
Solid Particles ◽  
Heated Wall ◽  
Wall Region ◽  
Flow And Heat Transfer ◽  
Particle Laden Flows ◽  
Near Wall

Direct numerical simulations of particle-laden flows in a spatially developing turbulent thermal boundary layer over an isothermally heated wall have been performed with realistic fully developed turbulent inflow boundary conditions. To the authors’ best knowledge, this is the first time the effects of inertial solid particles on turbulent flow and heat transfer in a flat-plate turbulent boundary layer have been investigated, using a two-way coupled Eulerian–Lagrangian method. Results indicate that the presence of particles increases the mean streamwise velocity and temperature gradients of the fluid in the near-wall region. As a result, the skin-friction drag and heat transfer are significantly enhanced in the particle-laden flows with respect to the single-phase flow. The near-wall sweep and ejection motions are suppressed by the particles and hence the Reynolds shear stress and wall-normal turbulent heat flux are attenuated, which leads to reductions in the production of the turbulent kinetic energy and temperature fluctuations. In addition, the coherence and spacing of the near-wall velocity and temperature streaky structures are distinctly increased, while the turbulent vortical structures appear to be disorganized under the effect of the particles. Moreover, the intensity of the streamwise vortices decreases monotonically with increasing particle inertia.

Analysis of the Visualization Region in Near-Wall Fluid Layer by High-Speed Infrared Thermography

2020 ◽  
Vol 75 (2) ◽  
pp. 143-147
Author(s):  
A. M. Shagiyanova ◽  
E. Yu. Koroteeva ◽  
I. A. Znamenskaya ◽  
M. E. Dashyan ◽  
L. A. Blagonravov ◽  
...  
Keyword(s):  
Infrared Thermography ◽  
High Speed ◽  
Fluid Layer ◽  
Near Wall

Incipient Flow Boiling in a Vertical Channel With a Wavy Wall

2010 ◽  
Author(s):  
T. Netz ◽  
R. Shalem ◽  
J. Aharon ◽  
G. Ziskind ◽  
R. Letan
Keyword(s):  
Heat Transfer ◽  
Temperature Field ◽  
High Speed ◽  
Flow Boiling ◽  
Heated Surface ◽  
Vertical Channel ◽  
Infrared Camera ◽  
Heat Fluxes ◽  
Heated Wall ◽  
Boiling Incipience

In the present study, incipient flow boiling of water is studied experimentally in a square-cross-section vertical channel. Water, preheated to 60–80 degrees Celsius, flows upwards. The channel has an electrically heated wall, where the heat fluxes can be as high as above one megawatt per square meter. The experiment is repeated for different water flow rates, and the maximum Reynolds number reached in the present study is 27,300. Boiling is observed and recorded using a high-speed digital video camera. The temperature field on the heated surface is measured with an infrared camera and a software is used to obtain quantitative temperature data. Thus, the recorded boiling images are analyzed in conjunction with the detailed temperature field. The dependence of incipient boiling on the flow and heat transfer parameters is established. For a flat wall, the results for various velocities and subcooling conditions agree well with the existing literature. Furthermore, three different wavy heated surfaces are explored, having the same pitch of 4mm but different amplitudes of 0.25mm, 0.5mm and 0.75mm. The effect of surface waviness on single-phase heat transfer and boiling incipience is shown. The differences in boiling incipience on various surfaces are elucidated, and the effect of wave amplitude on the results is discussed.

Numerical Study on Near-Wall Natural Convection Over a Microscale Heating Wire

2012 ◽  
Author(s):  
Leping Zhou ◽  
Yunfang Zhang ◽  
Lijun Yang ◽  
Xiaoze Du ◽  
Minami Yoda ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Numerical Study ◽  
Heat Transfer Process ◽  
Brownian Diffusion ◽  
Wall Region ◽  
Two Phase ◽  
Heating Wire ◽  
Transfer Problems ◽  
Near Wall

The study of the natural convection over a very small heat sources is important in the analysis of heat transfer problems in the electronics industry. However, the characteristics of the spatial distribution of the velocity in the near wall region, which is crucial to the mechanisms of heat transfer process in natural convection around a microscale object, is not well understood. In this investigation, the microscale natural convection in the near wall region of a platinum micro heat source was investigated numerically, using FLUENT, a commercially available computational fluid dynamics (CFD) software, and compared with corresponding experimental results. The influence of the nanoparticles on the natural convection was observed using the single-phase or two-phase models available in FLUENT. The temperature and velocity fields were obtained, with which the Brownian diffusion coefficient was deduced. The results indicate that the temperature gradient induced Brownian diffusion and thermophoresis in the near wall region plays an important role in the microscale natural convection in the water/nanoparticle mixture investigated and are in good agreement with the results from a corresponding experimental investigation.

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