scholarly journals Improvement of marina design technology using hydrodynamic models

2013 ◽  
Vol 6 (1) ◽  
pp. 63-72
Keyword(s):  
Mathematical Model ◽  
Flow Field ◽  
Flow Rate ◽  
Small Dimension ◽  
Water Circulation ◽  
Minor Importance ◽  
Hydrodynamic Models ◽  
Design Technology ◽  
Flow Rates ◽  
General Behavior

Á mathematical model is applied to calculate the water circulation in the marina of Latsi in Cyprus. The flow field in the marina shows the general behavior of coastal, wind driven flows, being strongly influenced by the characteristics of the entrance of the marina. The small dimension and the location of the entrance do not permit the inflow or outflow of significant flow rates, thus resulting to long flushing times. The use of two openings has been investigated. Computations show that the first opening plays a very important role, while the effect of the second opening is only of local and minor importance. This behavior is due to the orientation and the position of these openings with respect to the entrance. The use of the first opening results to a significant increase of the flow-rate passing through the inner part of the marina, which increases the magnitude of the velocities and reduce the flushing times. The use of the second opening leads to a significant short-circuiting path of the flow between the opening and the entrance. The first opening has been proposed for construction.

scholarly journals Influence of mineralization and injection flow rate on flow patterns in three-dimensional porous media

2019 ◽  
Vol 21 (27) ◽  
pp. 14605-14611 ◽  
Author(s):  
R. Moosavi ◽  
A. Kumar ◽  
A. De Wit ◽  
M. Schröter
Keyword(s):  
Porous Media ◽  
Flow Field ◽  
Flow Rate ◽  
Three Dimensional ◽  
Flow Patterns ◽  
Low Flow ◽  
Flow Rates ◽  
Injection Flow Rate ◽  
Injection Flow

At low flow rates, the precipitate forming at the miscible interface between two reactive solutions guides the evolution of the flow field.

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 Analysis of a novel high performance induction air heater

2018 ◽  
Vol 22 (Suppl. 3) ◽  
pp. 843-853 ◽  
Author(s):  
Umit Unver ◽  
Ahmet Yuksel ◽  
Alper Kelesoglu ◽  
Fikret Yuksel ◽  
Halil Unver
Keyword(s):  
Flow Field ◽  
Cross Section ◽  
Flow Rate ◽  
Thermal Efficiency ◽  
High Performance ◽  
Control Volume ◽  
Thermal Power ◽  
Heat Losses ◽  
Flow Rates ◽  
Air Mass

This study represents an experimental and numerical investigation of the enhanced prototypes of the induction air heaters. For this purpose, flow field is enhanced in order to avoid turbulence. The air mass flow rate, outlet construction and the application of insulation of the outer surface of the heater were selected as the performance enhancing parameters. Depending on the exit construction, the new designed prototypes are named as K-2 and K-3. Experiments were performed under two groups for three various flow rates. In the first group, non-insulation situation is examined. In the second group tests, insulation is applied to the outside of windings and inlet-outlet flaps which constitute the boundary of the control volume for the prevention of heat losses. The increasing flow rate boosted the thermal efficiency by 9%. Each of insulation and enlarging exit cross section increased the thermal efficiency by 13%. It was observed that the thermal power transferred to air with the new prototypes increased about 246 W more than the previous designs. The thermal efficiencies of the K-2 and K-3 type heaters were calculated as 77.14% and 87.1%, respectively.

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.

Experimental Investigation of Air Flow Through a Perforated Tile in a Raised Floor Data Center

2015 ◽  
Vol 137 (1) ◽  
Author(s):  
Vaibhav K. Arghode ◽  
Yogendra Joshi
Keyword(s):  
Flow Field ◽  
Flow Rate ◽  
Air Flow ◽  
Base Case ◽  
Flow Rates ◽  
Cold Air ◽  
Air Jet ◽  
Image Velocimetry ◽  
Flow Features ◽  
Staggered Arrangement

Raised floor data centers supply cold air from a pressurized plenum to the server racks through perforated floor tiles. Hence, the design of an efficient air delivery scheme requires better understanding of the flow features, through and above the perforated tiles. Different tiles with circular pores in a staggered arrangement and with the same thickness are considered. Tile sheet porosities of 23% and 40%, air flow rates of 0.56 m3/s (1177 CFM) and 0.83 m3/s (1766 CFM), and pore sizes of 3.18 mm (1/8 in.) and 6.35 mm (1/4 in.) are investigated. Tiles with 38.1 mm (1.5 in.) region blocked along the edges is compared to the base case with 12.7 mm (0.5 in.) blocked edges. Width reduced to 0.46 m (1.5 ft) from standard width of 0.61 m (2 ft) is also examined. Reduced tile width is used to simulate 0.91 m (3 ft) cold aisle instead of standard 1.22 m (4 ft) cold aisle, with potential to save floor space. A case where the rack is recessed by 76.2 mm (3 in.) from the tile edge is also included in the investigation, as there is a possibility of having racks nonadjacent to the tile edges. Particle image velocimetry (PIV) technique is used to characterize the flow field emerging from a perforated tile and entering the adjacent rack. Experiments suggest that lower tile porosity significantly increases cold air bypass from the top, possibly due to higher air jet momentum above the tile, as compared to a tile with higher porosity. For the air flow rates investigated here, the flow field was nearly identical and influence of flow rate was nondistinguishable. The influence of pore size was non-negligible, even when the porosity and flow rate for the two cases were same. Larger blockage of the tile edges resulted in higher cold air bypass from the top. Reduction in the tile width showed improved air delivery to the rack with considerably reduced cold air bypass. Recessing the rack did not affect the flow field significantly.

scholarly journals Study on Thermal Effect of Nozzle Flowmeter Based on Fluid-Solid Coupling Method

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Liang-Huai Tong ◽  
Su-Lu Zheng ◽  
Yu-Liang Zhang ◽  
Yan-Juan Zhao ◽  
Kai-Yuan Zhang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Numerical Calculation ◽  
Flow Field ◽  
Pressure Distribution ◽  
Thermal Effect ◽  
Flow Rate ◽  
Dynamic Stress ◽  
Transfer Effect ◽  
Coupling Method ◽  
Flow Rates

Nozzle flowmeter is widely used in industry. In this paper, in order to study the influence of different flow rates and inner wall temperatures on the thermal effect and flow field of the nozzle flowmeter, the fluid-solid coupling numerical calculation of the thermal effect and flow field of nozzle flowmeter is carried out under four different flow rates and five different inner wall temperatures. It is found that, with the increase of flow rate, the heat transfer effect of the nozzle flowmeter is weakened under different inner wall temperatures. The pressure distribution in the fluid domain, the dynamic stress, and fluid-induced vibration deformation generated by the fluid of the nozzle flowmeter are less affected by inner wall temperatures.

Experimental Study of Ingestion in the Rotor-Stator Disk Cavity of a Subscale Axial Turbine Stage

2014 ◽  
Author(s):  
J. Balasubramanian ◽  
P. S. Pathak ◽  
J. K. Thiagarajan ◽  
P. Singh ◽  
R. P. Roy ◽  
...  
Keyword(s):  
Flow Field ◽  
Flow Rate ◽  
Discharge Coefficient ◽  
Computational Effort ◽  
Radial Clearance ◽  
Turbine Stage ◽  
Flow Rates ◽  
Axial Turbine ◽  
Discharge Coefficients ◽  
Purge Flow

While it is widely recognized that ingestion of hot gas from the main annulus of axial gas turbine stages into rotor-stator disk cavities depend strongly on the unsteadiness of the prevailing flow field, the large computational effort needed to simulate the flow field renders its use in the design of turbine internal air system and seals difficult. As an alternative, considerable effort has been devoted in recent years to develop simple orifice models of disk cavity rim seals based on time-averaged flow information; these models contain empirical discharge coefficients for ingestion into and egress from the cavities. The present experimental work in a subscale axial turbine stage reports a simple orifice model of an axially-overlapping radial-clearance seal at the disk cavity rim and values of the discharge coefficients over a range of purge flow rate supplied to the cavity. In the experiments, the ingestion process was dominated by the main gas annulus flow. Time-averaged static pressure distribution was measured in the main annulus and in the disk cavity; the driving force for ingestion and egress was taken to be the pressure differential between the main annulus and the rim cavity at prescribed locations. Time-averaged ingestion was measured using the tracer gas technique; the pressure and ingestion data were combined to obtain the ingestion and egress discharge coefficients at several purge flow rates. The location on the vane platform 1mm upstream of its lip represented the main gas annulus pressure in the calculation of discharge coefficients. In the rim cavity, two locations on the stator, one in the ‘seal region’ and the other slightly inward radially, were prescribed to represent the rim cavity pressure as well as the sealing effectiveness. Two corresponding sets of ingestion and egress discharge coefficients are reported for the various purge flow rates. The ingestion discharge coefficient obtained using the seal region location in the rim cavity decreased as the purge flow rate increased; the corresponding egress discharge coefficient increased with purge flow rate. For the rim cavity location slightly inward radially from the seal region, the egress discharge coefficient maintained the same trend; however, the ingestion discharge coefficient decreased only slightly as the purge flow rate increased. It is suggested that the seal region location in the rim cavity is the more appropriate location in calculating the rim seal discharge coefficients. The ratio of ingestion to egress discharge coefficients exhibited considerable variation with purge flow rate.

Study of the Flow Field and Performances of a Centrifugal Pump During Unstable Operating Conditions by CFD

2015 ◽  
Author(s):  
Romain Prunières ◽  
Neo Imai ◽  
Yasuhiro Inoue ◽  
Takashi Okihara ◽  
Takahide Nagahara
Keyword(s):  
Flow Field ◽  
Flow Rate ◽  
Experimental Tests ◽  
Operating Conditions ◽  
Low Flow ◽  
Performance Curve ◽  
Centrifugal Pumps ◽  
Flow Rates ◽  
Computational Fluid Dynamics Cfd ◽  
Local Dent

Centrifugal pumps curve instability, characterized by a local dent and uprising head curve, often causes severe problems such as vibrations and noises. At low flow rates, stability of performance curve is necessary for reliable operation of the pump. Most of the studies regarding centrifugal pumps curves instability focus on flow rate around 60 % of the best efficiency flow rate. The purpose of present investigation is to analyse the causes of the occurrence of performance curve instability by means of Computational Fluid Dynamics (CFD) and to understand the mechanism of such instability at flow rates around 30 % of best efficiency flow rate. In order to understand the causes of the performance curve instability, two impellers with different outlet shape are analysed. During experimental tests, performance curve instability appeared around 30 % of the best efficiency flow rate on the first impeller while the second impeller remains stable. CFD analysis also shows unstable performance curve for the first impeller, and stable for the second one. Hence, a detailed analysis of the flow field of the two impellers and a quantitative comparison are performed in order to characterize the instability phenomenon.

Numerical Model for the Unsteady Flow Features of a Squirrel Cage Fan

2009 ◽  
Author(s):  
Rafael Ballesteros-Tajadura ◽  
Francisco Israel Guerras Colo´n ◽  
Sandra Velarde-Sua´rez ◽  
Jesu´s Manuel Ferna´ndez Oro ◽  
Katia Mari´a Argu¨elles Di´az ◽  
...  
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Flow Rate ◽  
Flow Distribution ◽  
Experimental Tests ◽  
Centrifugal Fan ◽  
Flow Rates ◽  
Squirrel Cage ◽  
Flow Features ◽  
Separation Zones

This paper shows a numerical research on the unsteady flow field inside a squirrel cage fan. The studied features are both the instantaneous flow fields and the average fluid flow associated to the blade passage frequency. The squirrel cage fan studied is a small centrifugal fan with a twin impeller configuration, each with 23 forward curved blades. The blades chord is 0.013 m and each impeller has a diameter of 0.08 m and a width of 0.094 m. The impellers operate inside an external spiral casing with a rectangular exit, followed by the outlet duct. A first series of experimental tests were performed in order to characterize the unit. The performance curves (head, power and efficiency versus flow rate) were measured. These tests show a nominal flow rate at around 0.098 m3/s and a specific speed ωs = 1.9. From there on, three different flow rates were considered to study different flow behaviours in the impeller. In parallel with the mentioned experimental study, the unsteady 3D flow field inside the fan equipped with the same impeller was modelled for the referred flow rates, by means of the commercial CFD code FLUENT. To facilitate the modification of any geometrical feature, the mesh of the modelled fan was divided in several regions: inlet duct, impeller, volute and diffuser with outlet duct. The main goal of the paper is to show the numerical results obtained on the absolute and relative frames. Three main flow features will be analysed: the inlet flow distribution, the blade to blade field and the impeller exit flow. At the fan inlet, special care will be taken to detect possible recirculation or separation zones. On the other hand, and for each studied flow rate, the distribution of outlet flow field is also analysed. Conclusions on flow uniformity are drawn.

scholarly journals Hyperfiltration and inner stripe hypertrophy may explain findings by Gamble and coworkers

2010 ◽  
Vol 298 (4) ◽  
pp. F962-F972 ◽  
Author(s):  
Anita T. Layton ◽  
Thomas L. Pannabecker ◽  
William H. Dantzler ◽  
Harold E. Layton
Keyword(s):  
Mathematical Model ◽  
Boundary Conditions ◽  
Transport Properties ◽  
Flow Rate ◽  
Collecting Duct ◽  
Urine Osmolality ◽  
Urine Flow ◽  
Supplemental Feeding ◽  
Duct System ◽  
Flow Rates

Simulations conducted in a mathematical model were used to exemplify the hypothesis that elevated solute concentrations and tubular flows at the boundary of the renal outer and inner medullas of rats may contribute to increased urine osmolalities and urine flow rates. Such elevated quantities at that boundary may arise from hyperfiltration and from inner stripe hypertrophy, which are correlated with increased concentrating activity (Bankir L, Kriz W. Kidney Int. 47: 7–24, 1995). The simulations used the region-based model for the rat inner medulla that was presented in the companion study (Layton AT, Pannabecker TL, Dantzler WH, Layton HE. Am J Physiol Renal Physiol 298: F000–F000, 2010). The simulations were suggested by experiments which were conducted in rat by Gamble et al. (Gamble JL, McKhann CF, Butler AM, Tuthill E. Am J Physiol 109: 139–154, 1934) in which the ratio of NaCl to urea in the diet was systematically varied in eight successive 5-day intervals. The simulations predict that changes in boundary conditions at the boundary of the outer and inner medulla, accompanied by plausible modifications in transport properties of the collecting duct system, can significantly increase urine osmolality and flow rate. This hyperfiltration-hypertrophy hypothesis may explain the finding by Gamble et al. that the maximum urine osmolality attained from supplemental feeding of urea and NaCl in the eight intervals depends on NaCl being the initial predominant solute and on urea being the final predominant solute, because urea in sufficient quantity appears to stimulate concentrating activity. More generally, the hypothesis suggests that high osmolalities and urine flow rates may depend, in large part, on adaptive modifications of cortical hemodynamics and on outer medullary structure and not entirely on an extraordinary concentrating capability that is intrinsic to the inner medulla.

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