Swimming speed of zebrafish in jet-stirred turbulence

In the nighttime stable boundary layer (SBL), shear and turbulence are generated in the layer between the maximum of the low-level jet (LLJ) and the earth's surface. Here, it is investigated whether gross properties of the LLJ—its height and speed—could be used to diagnose turbulence intensities in this subjet layer. Data on the height and speed of the LLJ maximum were available at high vertical and temporal resolution using the high-resolution Doppler lidar (HRDL). These data were used to estimate a subjet layer shear, which was computed as the ratio of the speed to the height of the jet maximum, and a jet Richardson number RiJ, averaged at 15-min intervals for 10 nights when HRDL LLJ data were available for this study. The shear and RiJ values were compared with turbulence kinetic energy (TKE) values measured near the top of the 60-m tower at the Cooperative Atmosphere–Surface Exchange Study-1999 (CASES-99) main site. TKE values were small for RiJ greater than 0.4, but as RiJ decreased to less ...

In this study, Gluconacetobacter Xylinus was used to produce BC (bacterial cellulose) both in static and dynamic culture conditions. Critical TKE (turbulent kinetic energy) values were estimated through CFD simulation for all the agitator rotation speeds of the bioreactor adopted in this research. TKE value of maximum 0.03 mSUP2/SUP/sSUP2/SUP lead to the highest yield of BC, above which BC production drastically diminished. The pellicle size of BC and water content decreased with TKE value. The experimental and CFD results show that TKE values above 0.09 mSUP2/SUP/sSUP2/SUP elicit short fibrous BC production and transformation of cells to the mutant counterparts.

Field experimental study of traffic-induced turbulence on highways

Stirring in bioreactors is an important element for the efficient cultivation of cell cultures in biotechnological production. But high-speed stirrers can create high level of shear stresses that negatively affect microorganisms. Therefore, it is important to develop the design of new stirring devices to minimize the negative impact of shear stresses on cells during cultivation. The purpose of this study is to analyze the effect of the designs of turbine stirring devices, proposed by authors, on the parameters of the stirring process during the cultivation of cell cultures by methods of computer modeling. The computer modeling was performed in ANSYS for the process of liquid stirring in a bioreactor. Two new designs of turbine stirrers have been proposed. The idea of the new design is to divide the working blade into two, i.e. to create a cutout in the blade. In the first case, the cutout is a rectangle, in the second - a parallelogram. To compare the efficiency of the proposed designs, we also modeled the stirring with a classical turbine 6-blade stirrer. Based on the modeling results, were obtained contours of the velocity distribution, turbulent kinetic energy, shear strain rate, velocity vectors, and ISO-surfaces forming the core of the rotation vortex. It was found that the presence of cutouts in the turbine stirrer does not lead to a decrease in the velocity of the main flows and redistribution of motion vectors, but significantly reduces the value of turbulent kinetic energy from and shear strain rate. The maximum value of turbulent kinetic energy for the classical stirrer is 2.489 m2/s2, while for the stirrers with cutouts it barely reaches 1.245 m2/s2. The shear stresses decrease by 10 % from 19.63·10-3 Pa for the classical design to 17.67·10-3 Pa for the stirrer with parallelogram-shaped cutouts. The further development of this study will be to analyze the influence of the geometric parameters of the stirrer with parallelogram-shaped cutouts on the qualitative indicators of stirring. The results obtained in this work can be used by engineers and technologists to design bioreactors with reduced values of shear stresses.

Chapter 2 - Turbulence generation by different types of impellers

Analysis on the influence of rotational speed to aerodynamic performance of vertical axis wind turbine

Spatiotemporal dynamics of the atmospheric kinetic energy and its components caused by the ordered and turbulent motions of air masses are estimated from minisodar measurements of three velocity vector components and their variances within the lowest 5–200 m layer of the atmosphere, with a particular emphasis on the turbulent kinetic energy. The layered structure of the total atmospheric kinetic energy has been established. From the diurnal hourly dynamics of the altitude profiles of the turbulent kinetic energy (TKE) retrieved from minisodar data, four layers are established by the character of the altitude TKE dependence, namely, the near-ground layer, the surface layer, the layer with a linear TKE increase, and the transitive layer above. In the first layer, the most significant changes of the TKE were observed in the evening hours. In the second layer, no significant changes in the TKE values were observed. A linear increase in the TKE values with altitude was observed in the third layer. In the fourth layer, the TKE slightly increased with altitude and exhibited variations during the entire observation period. The altitudes of the upper boundaries of these layers depended on the time of day. The MKE values were much less than the corresponding TKE values, they did not exceed 50 m2/s2. From two to four MKE layers were distinguished based on the character of its altitude dependence. The two-layer structures were observed in the evening and at night (under conditions of the stable atmospheric boundary layer). In the morning and daytime, the four-layer MKE structures with intermediate layers of linear increase and subsequent decrease in the MKE values were observed. Our estimates demonstrated that the TKE contribution to the total atmospheric kinetic energy considerably (by a factor of 2.5–3) exceeded the corresponding MKE contribution.

An analysis was conducted to investigate how reaction system turbulence affects the butadiene-isoprene copolymerization in the presence of the TiCl4 + Al(i-Bu)3 catalytic system. A model was developed, which integrates CFD simulations of TiCl4 + Al(i-Bu)3 particle breakage based on population balance equations with the kinetic modeling of the butadiene-isoprene copolymerization. It was established that an increase in turbulent kinetic energy leads to a reduction in catalyst particle size, an increase in active site concentration, an acceleration of the copolymerization process, and a decrease in the average molecular weights of the copolymer. Furthermore, catalytic activity correlates with both the average and maximum values of turbulent kinetic energy in the reaction system, whereas the effect of the average residence time of catalytic particles under turbulent conditions is insignificant. Based on these results, recommendations were provided for optimizing the impact of reaction system turbulence on TiCl4 + Al(i-Bu)3 particles to enhance the butadiene-isoprene copolymerization rate and achieve precise control over the molecular weight characteristics of the copolymer. The findings of this study can be applied to optimize the synthesis technology of the cis-1,4 butadiene-isoprene copolymer, which is used in the production of frost-resistant rubber.

The objective of the current work was to evaluate flow and turbulent kinetic energy in different transcatheter aortic valve implants using highly undersampled time-resolved multi-point 3-directional phase-contrast measurements (4D Flow MRI) in an in vitro setup. A pulsatile flow setup was used with a compliant tubing mimicking a stiff left ventricular outflow tract and ascending aorta. Five different implants were measured using a highly undersampled multi-point 4D Flow MRI sequence. Velocities and turbulent kinetic energy values were analysed and compared. Strong variations of turbulent kinetic energy distributions between the valves were observed. Maximum turbulent kinetic energy values ranged from 100 to over 500J/m3 while through-plane velocities were similar between all valves. Highly accelerated 4D Flow MRI for the measurement of velocities and turbulent kinetic energy values allowed for the assessment of hemodynamic parameters in five different implant models. The presented setup, measurement protocol and analysis methods provides an efficient approach to compare different valve implants and could aid future novel valve designs.

In order to study the influence of the presence of floodplain vegetations on the flow structure of compound open channels, a three-dimensional large eddy simulation model for compound open-channel flows with vegetations was established, and the flow motion of the compound open channel under the action of non-submerged vegetations was simulated. The simulation results are in good agreement with the previous numerical simulation results, indicating that the model established in this paper is reliable and effective in the numerical simulation of compound open-channel flows with vegetations. The influence of the presence of floodplain vegetations on the flow structure of compound open channels and the influence of different vegetation densities on the flow structure of compound open channels were analyzed. The results show that the presence of floodplain vegetations significantly changes the flow structure within the compound open-channel flow. Due to the presence of vegetations, the longitudinal average velocity of the floodplain decreases, the longitudinal average velocity of the main channel increases, the maximum values of turbulent kinetic energy and Reynolds stress at the junction of the main channel and the floodplain increase, the boundary shear stress on the main channel and the floodplain decreases, and the apparent shear stress increases. The higher the vegetation density, the smaller the longitudinal average velocity of the floodplain, the greater the intensity of the leftward shift of the maximum longitudinal average velocity of the main channel, the stronger the secondary flow, the greater the maximum values of turbulent kinetic energy and Reynolds stress near the confluence of the main channel and the floodplain, while the boundary shear stress of the main channel and the floodplain decreases, and the peak value of the apparent shear stress near the confluence of the main channel and the floodplain increases.

A total of seven versions of two-equation turbulence models (four versions of low Reynolds number k–ε model, one k–ω model and two versions of k–ε / k–ω blended models) are tested against the direct numerical simulation (DNS) data of a one-dimensional oscillatory boundary layer with flat crested free-stream velocity that results from a steep pressure gradient. A detailed comparison has been made for cross-stream velocity, turbulent kinetic energy (TKE), Reynolds stress, and ratio of Reynolds stress and turbulent kinetic energy. It is observed that the newer versions of k–ε model perform very well in predicting the velocity, turbulent kinetic energy, and Reynolds stress. The k–ω model and blended models underestimate the peak value of turbulent kinetic energy that may be explained by the Reynolds stress to TKE ratio in the logarithmic zone. The maximum bottom shear stress is well predicted by the k–ε model proposed by Sana et al. and the original k–ω model.

Variations in discharge and turbulent kinetic energy (TKE) were studied at a point‐source submarine groundwater discharge (SGD), within a fringing reef lagoon, from quadrature (neap) to syzygy (spring) tides. The principal factors affecting discharge and TKE variations were tides and waves. Field data indicated discharge, and TKE varied with high and low tides, and with quadrature and syzygy. Maximum discharge and TKE values were observed during low tides when the hydrostatic pressure over the jet was minimal, while the lowest discharge and TKE values were found at high tides. Syzygy tides produced consistent saltwater intrusion during high tides, while quadrature tides produced the greatest TKE values. In general, as the discharge intensified during low tides, jet temperatures decreased suggesting that waters originated further within the aquifer. At the same time jet salinities increased, suggesting a mixing of aquifer and seawater. To reconcile these two seemingly opposing views, it is proposed that the jet conduit is connected to a stratified chamber with seawater below brackish water. The greatest subtidal discharge occurred during quadrature tides. Syzygy produced low subtidal discharge driven by flow reversals (flow into the aquifer) observed throughout syzygy high tides in conjunction with the peak wave setup (>5 cm) observed during a storm. While tides were the primary driving force of the discharge, waves played a nonnegligible role. Wave effects on the discharge were most evident during syzygy high tides combined with a storm, when the subtidal spring discharge was weakest and salt intrusion developed.

Curved channels and aquatic vegetation are commonly present in the riverine environment. In this study, the effects of vegetation density and distribution on the hydrodynamic characteristics of a mixed layer developed over a 180-degree curved channel were investigated through flume experiments. Wooden sticks were used to simulate rigid vegetation distributed along the half side of the channel, and a 200 Hz acoustic Doppler velocimeter (ADV) was employed to measure the three-dimensional instantaneous velocity at five selected cross sections along the curved channel. Experimental results show that the vegetation covering the half of the channel significantly affects the hydrodynamic structure of the curved channel flow, and the unequal vegetation resistance induces the K-H instability at the vegetation and non-vegetation interface, resulting in a standard hyperbolic tangent function of streamwise velocity distribution along the lateral direction. The influence of curve position on turbulence kinetic energy is far greater than that of vegetation density and vegetation distribution. The peak value of turbulent kinetic energy is comprehensively affected by vegetation density and distribution, and the peak position of turbulent kinetic energy at the interface is changed by different vegetation distribution. The combined effect of the curve and the partly covered vegetation increases the mixing between the water bodies, enhancing turbulent kinetic energy, and vegetation along the concave bank plays a more significant role. For turbulent bursting, the inward and outward interactions are mainly bursting events in the vegetation area, while ejections and sweeps are dominant in the non-vegetation area. However, the critical vegetation condition to initiate large-scale coherent structure (LSS) in the mixed layer and the influence of flexible vegetation need to be further studied in the future.

Wind flow over the low-rise building models with gabled roofs having different pitch angles

Water transferring to the dam downstream creates high levels of kinetic energy. Stepped spillways are amongst the most effective spillways in reducing the kinetic energy of the flow moving towards the downstream. The geometry of the steps in stepped spillways can affect the reduction of kinetic energy of the flow transferring to the downstream. Therefore, in this study the effect of different number of steps and discharge on flow pattern especially energy dissipation were investigated. The VOF method was used to simulate the flow surface and the k-ε (RNG) turbulence model was used for flow turbulence simulation. Comparing the results obtained from the numerical simulation with the experimental data indicated an acceptable level of consistency. Comparing the obtained results showed that decreasing the number of the steps of pooled stepped spillways reduced flow velocity and increased the relative energy dissipation at the end of the spillway. Decreasing the number of steps increased the turbulent kinetic energy value. Also, the maximum turbulent kinetic energy was obtained near the step's pool. Moreover the results indicated that the value of turbulent kinetic energy increased along the spillway.