scholarly journals Numerical simulation and experiments on turbulent air flow around the semi-circular profile at zero angle of attack and moderate Reynolds number

2019 ◽  
Vol 188 ◽  
pp. 1-17 ◽  
Author(s):  
Sergey Isaev ◽  
Paul Baranov ◽  
Igor Popov ◽  
Alexander Sudakov ◽  
Alexander Usachov ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Air Flow ◽  
Angle Of Attack ◽  
Moderate Reynolds Number ◽  
Circular Profile ◽  
Turbulent Air Flow

Investigation of droplet-mediated sensible and latent heat fluxes in a turbulent air flow over a waved water surface by direct numerical simulation

2020 ◽  
Author(s):  
Oleg Druzhinin
Keyword(s):  
Numerical Simulation ◽  
Heat Flux ◽  
Direct Numerical Simulation ◽  
Latent Heat ◽  
Water Surface ◽  
Air Flow ◽  
Sensible Heat Flux ◽  
Heat Fluxes ◽  
Coupled Equations ◽  
Turbulent Air Flow

<p>The objective of the present study is to investigate sensible and latent heat transfer mediated by evaporating saline droplets in a turbulent air flow over a waved water surface by performing direct numerical simulation. Equations of the air-flow velocity, temperature and humidity are solved simultaneously with the two-way-coupled equations of individual droplets coordinates and velocities, temperatures and masses. Two different cases of air and water surface temperatures,T<sub>a</sub> = 27 <sup>0</sup>C, T<sub>s</sub> = 28 <sup>0</sup>C,  and T<sub>a</sub> = -10 <sup>0</sup>C, T<sub>s</sub> = 0 <sup>0</sup>C, are considered and conditionally termed as "tropical cyclone" (TC) and "polar low"  (PL) conditions, respectively. Droplets-mediated sensible and latent heat fluxes, Q<sub>S</sub> and Q<sub>L</sub>, are integrated along individual droplets Lagrangian trajectories and evaluated as distributions over droplet diameter at injection, d, and also obtained as Eulerian, ensemble-averaged fields. The results show that under TC-conditions, the sensible heat flux from droplets to air is negative whereas the latent heat flux is positive, and thus droplets cool and moisturize the carrier air. On the other hand, under PL-conditions, Q<sub>S</sub> and Q<sub>L</sub>  are both positive, and Q<sub>L</sub> – contribution is significantly reduced as compared to Q<sub>S</sub> - contribution. Thus in this case, droplets warm up the air. In both cases, the droplet-mediated enthalpy flux, Q<sub>S</sub><sub> </sub>+ Q<sub>L </sub>, is positive, vanishes for sufficiently small droplets (with diameters d ≤ 150 μm) and further increases with d. The results also show that the net fluxes are reduced with increasing wave slope.</p><p>This work is supported by the Ministry of Education and Science of the Russian Federation (Task No. 0030-2019-0020). Numerical algorithms were developed under the support of RFBR (Nos. 18-05-60299, 18-55-50005, 18-05-00265, 20-05-00322). Postprocessing was performed under the support of the Russian Science Foundation (No. 19-17-00209).</p>

A physical mechanism of the energy cascade in homogeneous isotropic turbulence

2008 ◽  
Vol 605 ◽  
pp. 355-366 ◽  
Author(s):  
SUSUMU GOTO
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Direct Numerical Simulation ◽  
Transfer Rate ◽  
Physical Mechanism ◽  
Isotropic Turbulence ◽  
Scale Space ◽  
Energy Cascade ◽  
Homogeneous Isotropic Turbulence ◽  
Moderate Reynolds Number

In order to investigate the physical mechanism of the energy cascade in homogeneous isotropic turbulence, the internal energy and its transfer rate are defined as a function of scale, space and time. Direct numerical simulation of turbulence at a moderate Reynolds number verifies that the energy cascade can be caused by the successive creation of smaller-scale tubular vortices in the larger-scale straining regions existing between pairs of larger-scale tubular vortices. Movies are available with the online version of the paper.

Regimes of tonal noise on an airfoil at moderate Reynolds number

2015 ◽  
Vol 780 ◽  
pp. 407-438 ◽  
Author(s):  
S. Pröbsting ◽  
F. Scarano ◽  
S. C. Morris
Keyword(s):  
Reynolds Number ◽  
Angle Of Attack ◽  
Suction Side ◽  
Small Scale ◽  
Noise Generation ◽  
Tonal Noise ◽  
Flow Topology ◽  
Trailing Edge ◽  
Moderate Reynolds Number ◽  
Two Sides

Tonal noise generated by airfoils at low to moderate Reynolds number is relevant for applications in, for example, small-scale wind turbines, fans and unmanned aerial vehicles. Coherent and convected vortical structures scattering at the trailing edge from the pressure or suction sides of the airfoil have been identified to be responsible for such tonal noise generation. Controversy remains on the respective significance of pressure- and suction-side events, along with their interaction for tonal noise generation. The present study surveys the regimes of tonal noise generation for low to moderate chord-based Reynolds number between $\mathit{Re}_{c}=0.3\times 10^{5}$ and $2.3\times 10^{5}$ and effective angle of attack between $0^{\circ }$ and $6.3^{\circ }$ for the NACA 0012 airfoil profile. Extensive acoustic measurements with smooth surface and with transition to turbulence forced by boundary layer tripping are presented. Results show that, at non-zero angle of attack, tonal noise generation is dominated by suction-side events at low Reynolds number and by pressure-side events at high Reynolds number. At smaller angle of attack, interaction between events on the two sides becomes increasingly important. Particle image velocimetry measurements complete the information on the flow field structure in the source region around the trailing edge. The influences of both angle of attack and Reynolds number on tonal noise generation are explained by changes in the mean flow topology, namely the presence and location of reverse flow regions on the two sides. Data gathered from experimental and numerical studies in the literature are reviewed and interpreted in view of the different regimes.

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