turbulence modulation
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2021 ◽  
Vol 932 ◽  
Author(s):  
Vikash Pandey ◽  
Dhrubaditya Mitra ◽  
Prasad Perlekar

We present a direct numerical simulation (DNS) study of buoyancy-driven bubbly flows in the presence of large-scale driving that generates turbulence. On increasing the turbulence intensity: (a) the bubble trajectories become more curved and (b) the average rise velocity of the bubbles decreases. We find that the energy spectrum of the flow shows a pseudo-turbulence scaling for length scales smaller than the bubble diameter and a Kolmogorov scaling for scales larger than the bubble diameter. We conduct a scale-by-scale energy budget analysis to understand the scaling behaviour observed in the spectrum. Although our bubbles are weakly buoyant, the statistical properties of our DNS are consistent with the experiments that investigate turbulence modulation by air bubbles in water.


2021 ◽  
Vol 33 (11) ◽  
pp. 113305
Author(s):  
Ping Wang ◽  
Qingqing Wei ◽  
Xiaojing Zheng

2021 ◽  
Vol 926 ◽  
Author(s):  
S. Silvestri ◽  
R. Pecnik

We present direct numerical simulations of developing turbulent channel flows subjected to thermal expansion or contraction downstream of a heated or cooled wall. Using different constitutive relations for viscosity we analyse the response of variable property flows to streamwise acceleration/deceleration by separating the effect of streamwise acceleration/deceleration from the effect of wall-normal property variations. We demonstrate that, beyond a certain streamwise location, the flow can be considered in a state of ‘quasi-equilibrium’ regarding semilocally scaled variables. As such, we claim that the development of turbulent quantities due to streamwise acceleration/deceleration is localized to the region of impulsive heating/cooling, while changes in turbulence occurring farther downstream can be attributed solely to property variations. This finding allows us to study turbulence modulation in accelerating/decelerating flows using the semilocal scaling framework. By investigating the energy redistribution among the turbulent velocity fluctuations, we conclude that a change in bulk streamwise velocity has a non-local effect which originates from the change in mean shear and modifies the energy pathways through velocity-pressure-gradient correlations. On the other hand, the wall-normal property gradients have a local effect and act through the modification of the viscous dissipation. We show that it is possible to superimpose and compare the two different effects when using the semilocal scaling framework.


2021 ◽  
Vol 33 (8) ◽  
pp. 083315
Author(s):  
Ping Wang ◽  
Jinchi Li ◽  
Xiaojing Zheng

2021 ◽  
Vol 922 ◽  
Author(s):  
Pedro Costa ◽  
Luca Brandt ◽  
Francesco Picano

Abstract


2021 ◽  
Vol 33 (6) ◽  
pp. 063321
Author(s):  
Yan Xia ◽  
Zhaowu Lin ◽  
Dingyi Pan ◽  
Zhaosheng Yu

Author(s):  
Andrew Bluestein ◽  
Douglas Bohl

Abstract Turbulent particle-laden flows are of interest due to their presence in many industrial and natural flows. The effect that the particles have on the turbulence of the fluid is referred to as turbulence modulation. Experimental data is lacking at Reynolds numbers greater than 100,000, and at dense loadings (FV > 1%). In this work, turbulent particle-laden flow over a deep cavity with an aspect ratio of 1, was studied at Reynolds numbers of 11,500 and 115,000, and particle loadings of 0%, 1%, 3%, and 5% by weight/volume (solid-phase specific gravity = 1). Super absorbent particles were used to create an index-matched environment with water as the working fluid. Data were acquired using 2-D planar particle image velocimetry (PIV) along the center span of the geometry. Mean and root-mean-square (rms) velocities were calculated for the fluid phase. The flow structures were identified and located using the gamma criteria. The results showed that the particle loading changed the locations of the recirculation regions within the cavity. The mean velocities were nominally unaffected by loading for a respective Reynolds number case. Prior literature suggested that the particles would attenuate the turbulence, however, the current data showed no single trend. Turbulence modulation of the flow was found to be sensitive to the Reynolds number and location within the flow field. The changes in the turbulence appeared to be primarily due to the differences in the location in the flow structures.


Author(s):  
Xu Chu ◽  
Wenkang Wang ◽  
Johannes Müller ◽  
Hendrik Von Schöning ◽  
Yanchao Liu ◽  
...  

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