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Turbulent Flows with Chemical Reaction
Published in Bart Merci, Tarek Beji, Fluid Mechanics Aspects of Fire and Smoke Dynamics in Enclosures, 2023
Turbulence is typically defined on the basis of a number of properties [13]: Randomness: there are fluctuations in the flow.Three-dimensionality: even if the mean flow is 2D or axisymmetric, the vortices or ‘eddies’ are always three-dimensional.There is a wide range of length scales and time scales in the flow. The largest scales are determined by the geometry at hand, while the smallest scales are determined by the Reynolds number. The smallest scales can easily be 10.000 times smaller than the largest scales.Turbulent mixing is very effective.There is strong diffusion and dissipation. Turbulence dies out quickly if not sustained by velocity gradients in the mean flow.There is an energy cascade, transferring energy from the mean flow (large scales) to turbulent fluctuations (to smaller and smaller scales). At the smallest scales, the ‘turbulence kinetic energy’ is dissipated into heat due to the viscous forces.
Introduction
Published in Mohamed Gad-el-Hak, MEMS, 2005
In both the chess problem and the turbulence problem, the further into the future one can optimize the problem the better (Figure 15.14). However, both problems get exponentially more difficult to optimize as the prediction horizon is increased. Because only intermediate-term optimization is tractable, representing the final objective in the cost functional is not always the best approach. In the chess problem, though the final aim is to capture the other player's king, it is most effective to adopt a mid-game strategy of establishing good board position and achieving material advantage. Similarly, if the turbulence control objective is reducing drag, Bewley et al. (2001) found that it is most effective along the way to minimize a finite-horizon cost functional related to the turbulent kinetic energy of the flow because the turbulent transport of momentum is responsible for inducing a substantial portion of the drag in a turbulent flow. In a sense, turbulence is the "cause" and high drag is the "effect," and it is most effective to target the "cause" in the cost functional when optimizations on only intermediate prediction horizons are possible.
Physics-Guided Deep Learning for Spatiotemporal Forecasting
Published in Anuj Karpatne, Ramakrishnan Kannan, Vipin Kumar, Knowledge-Guided Machine Learning, 2023
Rui Wang, Robin Walters, Rose Yu
Turbulence Kinetic Energy: In fluid dynamics, turbulence kinetic energy is the mean kinetic energy per unit mass associated with eddies in turbulent flow. Physically, the turbulence kinetic energy is characterised by measured root mean square velocity fluctuations, ((u′)2¯+(v′)2¯)/2,(u′)2¯=1T∑t=0T(u(t)−u¯)2
Flow and heat transfer of hydrocarbon fuel in the double-layer regenerative cooling channels
Published in Numerical Heat Transfer, Part A: Applications, 2023
Yuguang Jiang, Leqing Wang, Qilin Zhou, Nicolas Gascoin, Khaled Chetehouna, Wei Fan
The mechanism on heat transfer of double-layer-channel scheme is further presented from the perspective of detailed internal flow field of lower-layer channels (Figure 30). Cross sections with maximum bottom wall temperatures are selected as representatives. Comparing case H1/H2 = 1, case H1/H2 = 1/2, and case H1/H2 = 1/4, the near heated wall temperature gradient is smaller. In the range of y/H2 <0.65, the density of Case H1/H2 = 1 is lower. The velocity and turbulent kinetic energy are higher, which both benefit the heat transfer. Although fuel heat conductivity is lower in case H1/H2 = 1, it is neutralized by the above factors. The heat transfer of case H1/H2 = 1 is strongest.
Numerical Studies of Separation Performance of Knelson Concentrator for Beneficiation of Fine Coal
Published in International Journal of Coal Preparation and Utilization, 2021
Licheng Ma, Lubin Wei, Xueshuai Zhu, Darong Xu, Xinyu Pei, Hongchao Xue
In centrifugal force field, the effect of movement on the particle in solid-liquid two-phase flow is determined by the movement condition of the fluid. So the particle motion is depended on the fluid motion law. Figure 2 shows the snapshots of fluid configurations in rotation bowl. It depicts the contours of turbulence intensity of continuous phases obtained from the CFD simulation results. The rotation bowl is vacant (filled with air) at the beginning (t = 0 s). Then, feed flow is introduced through a central tube at the bottom simultaneously. The turbulent kinetic energy is the measure of turbulent intensity. According to the distribution of the turbulence intensity in the flow field, the flow control information can be obtained. As shown in Figure 2, the flow field of turbulent intensity can be divided into the upper part at the bottom of rotation wall and on the wall of the riffle, and lower part inside rotation wall.
Turbulent flow characteristics for enhanced thermal mixing in square and triangular jets
Published in Numerical Heat Transfer, Part A: Applications, 2020
From the viewpoint of flow mixing, the turbulent kinetic energy is an indicator of small-scale mixing. Figure 6 shows the axial distributions of the cross-sectional averaged turbulent intensity () for different inlet nozzles. As can be observed, the turbulent kinetic energies for noncircular jets are more enhanced than that of the round jet. Consequently, the kavg values for noncircular jets are quickly maximized near the inlet plane. It is interesting that the axial positions having the maximum value of kavg roughly coincide with the Lp value in Figure 3(a). For the initial and transitional regions of x/De≤ 10, the kavg values for noncircular jets rapidly increase, whereas the difference between the kavg values is very weak for the self-similar region. These results show that the change of the nozzle shape has great effects on the mixing for initial and transitional regions, although it does not affect the self-similar region.