scholarly journals Numerical investigation of the turbulence characteristics and energy dissipation mechanism of baffle drop shafts

2021 ◽  
Author(s):  
Qinghua Yang ◽  
Qian Yang
Keyword(s):  
Energy Dissipation ◽  
Flow Rate ◽  
High Energy ◽  
Design Flow ◽  
Low Flow ◽  
Turbulence Characteristics ◽  
Energy Dissipation Mechanism ◽  
Dissipation Mechanism ◽  
Drop Flow ◽  
Free Drop

Abstract The baffle drop shaft is widely used in deep tunnel drainage system due to its fine applicability and high energy dissipation. To fully study the turbulence characteristics and energy dissipation mechanism of baffle drop shafts, a 1:25 scale physical model test and the numerical simulation based on the Realizable k-ε model and Volume of Fluid (VOF) method were performed. The results showed that a baffle spacing that is too dense or too sparse is not conducive to energy dissipation and discharge. The minimum baffle spacing is the optimal structural design at the design flow rate when the flow regime is free-drop flow. The energy dissipation calculation model established in this paper has high accuracy for calculating the energy dissipation rate on the baffles in free-drop flow. The energy dissipation modes of the shaft can be divided into inlet energy dissipation, baffle energy dissipation, and shaft-bottom energy dissipation. Baffles play a major role in the energy dissipation at low flow rates, and the proportions of inlet and shaft-bottom energy dissipation increase with the increase in flow rate.

Turbulence Measurements in a Centrifugal Pump With a Synchronously Orbiting Impeller

1991 ◽  
Author(s):  
Ronald D. Flack ◽  
Steven M. Miner ◽  
Ronald J. Beaudoin
Keyword(s):  
Centrifugal Pump ◽  
Reynolds Stress ◽  
Flow Rate ◽  
Cross Product ◽  
Design Flow ◽  
Low Flow ◽  
Rate Variation ◽  
Flow Rates ◽  
The Individual ◽  
Design Flow Rate

Turbulence profiles were measured in a centrifugal pump with an impeller with backswept blades using a two directional laser velocimeter. Data presented includes radial, tangential, and cross product Reynolds stresses. Blade to blade profiles were measured at four circumferential positions and four radii within and one radius outside the four bladed impeller. The pump was tested in two configurations; with the impeller running centered within the volute, and with the impeller orbiting with a synchronous motion (ε/r2 = 0.016). Flow rates ranged from 40% to 106% of the design flow rate. Variation in profiles among the individual passages in the orbiting impeller were found. For several regions the turbulence was isotropic so that the cross product Reynolds stress was low. At low flow rates the highest cross product Reynolds stress was near the exit. At near design conditions the lowest cross product stress was near the exit, where uniform flow was also observed. Also, near the exit of the impeller the highest turbulence levels were seen near the tongue. For the design flow rate, inlet turbulence intensities were typically 9% and exit turbulence intensities were 6%. For 40% flow capacity the values increased to 18% and 19%, respectively. Large local turbulence intensities correlated with separated regions. The synchronous orbit did not increase the random turbulence, but did affect the turbulence in the individual channels in a systematic pattern.

scholarly journals Interfacial strength-controlled energy dissipation mechanism and optimization in impact-resistant nacreous structure

2019 ◽  
Vol 163 ◽  
pp. 107532 ◽  
Author(s):  
Kaijin Wu ◽  
Zhijun Zheng ◽  
Shuaishuai Zhang ◽  
Linghui He ◽  
Hongbin Yao ◽  
...  
Keyword(s):  
Energy Dissipation ◽  
Interfacial Strength ◽  
Energy Dissipation Mechanism ◽  
Dissipation Mechanism

Turbulence Measurements in a Centrifugal Pump With a Synchronously Orbiting Impeller

1992 ◽  
Vol 114 (2) ◽  
pp. 350-358 ◽  
Author(s):  
R. D. Flack ◽  
S. M. Miner ◽  
R. J. Beaudoin
Keyword(s):  
Centrifugal Pump ◽  
Reynolds Stress ◽  
Flow Rate ◽  
Cross Product ◽  
Design Flow ◽  
Low Flow ◽  
Rate Variation ◽  
Flow Rates ◽  
The Individual ◽  
Design Flow Rate

Turbulence profiles were measured in a centrifugal pump with an impeller with backswept blades using a two-directional laser velocimeter. Data presented include radial, tangential, and cross product Reynolds stresses. Blade-to-blade profiles were measured at four circumferential positions and four radii within and one radius outside the four-bladed impeller. The pump was tested in two configurations: with the impeller running centered within the volute, and with the impeller orbiting with a synchronous motion (ε/r2 = 0.016). Flow rates ranged from 40 to 106 percent of the design flow rate. Variation in profiles among the individual passages in the oribiting impeller were found. For several regions the turbulence was isotropic so that the cross product Reynolds stress was low. At low flow rates the highest cross product Reynolds stress was near the exit. At near-design conditions the lowest cross product stress was near the exit, where uniform flow was also observed. Also, near the exit of the impeller the highest turbulence levels were seen near the tongue. For the design flow rate, inlet turbulence intensities were typically 9 percent and exit turbulence intensities were 6 percent. For 40 percent flow capacity the values increased to 18 and 19 percent, respectively. Large local turbulence intensities correlated with separated regions. The synchronous orbit did not increase the random turbulence, but did affect the turbulence in the individual channels in a systematic pattern.

scholarly journals Energy dissipative photoprotective mechanism of carotenoid spheroidene from the photoreaction center of purple bacteria Rhodobacter sphaeroides

2015 ◽  
Vol 17 (36) ◽  
pp. 23468-23480 ◽  
Author(s):  
Sundaram Arulmozhiraja ◽  
Naoki Nakatani ◽  
Akira Nakayama ◽  
Jun-ya Hasegawa
Keyword(s):  
Energy Dissipation ◽  
Rhodobacter Sphaeroides ◽  
Purple Bacteria ◽  
Minimum Energy ◽  
Intersystem Crossing ◽  
Triplet Energy ◽  
Energy Dissipation Mechanism ◽  
Dissipation Mechanism ◽  
Crossing Point

Triplet energy dissipation mechanism of a carotenoid: just bond twisting and stretching lead to minimum energy intersystem crossing point.

scholarly journals Investigation of the Flow Field in the Vicinity of an Axial Flow Fan During Low Flow Rates

2014 ◽  
Author(s):  
Francois G. Louw ◽  
Theodor W. von Backström ◽  
Sybrand J. van der Spuy
Keyword(s):  
Flow Field ◽  
Numerical Simulations ◽  
Flow Rate ◽  
Axial Flow ◽  
Operating Conditions ◽  
Design Flow ◽  
Low Flow ◽  
Axial Flow Fan ◽  
Free Vortex ◽  
Flow Rates

Large axial flow fans are used in forced draft air cooled heat exchangers (ACHEs). Previous studies have shown that adverse operating conditions cause certain sectors of the fan, or the fan as a whole to operate at very low flow rates, thereby reducing the cooling effectiveness of the ACHE. The present study is directed towards the experimental and numerical analyses of the flow in the vicinity of an axial flow fan during low flow rates. This is done to obtain the global flow structure up and downstream of the fan. A near-free-vortex fan, designed for specific application in ACHEs, is used for the investigation. Experimental fan testing was conducted in a British Standard 848, type A fan test facility, to obtain the fan characteristic. Both steady-state and time-dependent numerical simulations were performed, depending on the operating condition of the fan, using the Realizable k-ε turbulence model. Good agreement is found between the numerically and experimentally obtained fan characteristic data. Using data from the numerical simulations, the time and circumferentially averaged flow field is presented. At the design flow rate the downstream fan jet mainly moves in the axial and tangential direction, as expected for a free-vortex design criteria, with a small amount of radial flow that can be observed. As the flow rate through the fan is decreased, it is evident that the down-stream fan jet gradually shifts more diagonally outwards, and the region where reverse flow occur between the fan jet and the fan rotational axis increases. At very low flow rates the flow close to the tip reverses through the fan, producing a small recirculation zone as well as swirl at certain locations upstream of the fan.

scholarly journals Effect of Two- and Three-Dimensionally Designed Guide Vanes with Different Camber Length on Static Pressure Recovery of a Wall-Mounted Axial Fan

Processes ◽  
2021 ◽  
Vol 9 (9) ◽  
pp. 1595
Author(s):  
Yong-In Kim ◽  
Yong-Uk Choi ◽  
Cherl-Young Jeong ◽  
Kyoung-Yong Lee ◽  
Young-Seok Choi
Keyword(s):  
Flow Rate ◽  
Guide Vane ◽  
Dynamic Pressure ◽  
Pressure Rise ◽  
Design Flow ◽  
Low Flow ◽  
Axial Fan ◽  
Flow Angle ◽  
Numerical Effort ◽  
Vane Angle

This study was based on a numerical effort to use the motor support (prop) as a guide vane when the motor of a wall-mounted axial fan was located at the fan outlet while maintaining the structural and spatial advantage. The design for the guide vane followed two- and three-dimensional methods. The inlet vane angle, meridional length (total), and meridional length with a vane angle of zero (0) degrees (linear) were considered as design variables. At the design and some low flow rate points, the 2D design offered the most favorable performance when the meridional length with a vane angle of zero (0) degrees (linear) was 30% based on total length, and was the worst for 70%. The 3D design method applied in this study did not outperform the 2D design. In the 2D design concept, averaging the flow angle for the entire span at the design flow rate could ensure a better pressure rise over a more comprehensive flow rate range than weighting the flow angle for a specific span. In addition, the numerical results were validated through an experimental test, with an important discussion of the swirl (dynamic pressure) component. The influence of the inlet motor and turbulence model are presented as a previous confirmation.

Compressible Simulation of Flow and Sound Around a Small Axial-Flow Fan With Flow Through Casing Slits

2020 ◽  
Vol 142 (10) ◽  
Author(s):  
Hiroshi Yokoyama ◽  
Katsutake Minowa ◽  
Kohei Orito ◽  
Masahito Nishikawara ◽  
Hideki Yanada
Keyword(s):  
Flow Field ◽  
Flow Rate ◽  
Aerodynamic Performance ◽  
Design Flow ◽  
Low Flow ◽  
Axial Fan ◽  
Flow Rates ◽  
Blade Tip ◽  
Flow Through ◽  
Design Flow Rate

Abstract Small axial fans are used for cooling electronic equipment and are often installed in a casing with various slits. Direct aeroacoustic simulations and experiments were performed with different casing opening ratios to clarify the effects of the flow through the casing slits on the flow field and acoustic radiation around a small axial fan. Both the predicted and measured results show that aerodynamic performance deteriorates at and near the design flow rate and is higher at low flow rates by completely closing the casing slits compared with the fan in the casing with slits. The predicted flow field shows that the vortical structures in the tip vortices are spread by the suppression of flow through the slits at the design flow rate, leading to the intensification of turbulence in the blade wake. Moreover, the pressure fluctuations on the blade surface are intensified, which increases the aerodynamic sound pressure level. The suppression of the outflow of pressurized air through the downstream part of the slits enhances the aerodynamic performance at low flow rates. Also, the predicted surface streamline at the design flow rate shows that air flows along the blade tip for the fan with slits, whereas the flow toward the blade tip appears for the fan without slits. As a result, the pressure distributions on the blade and the torque exerted on the fan blade are affected by the opening ratio of slits.

Sign in / Sign up

Export Citation Format

Share Document