scholarly journals Empirical, Dimensional and Inspectional Analysis in the Design of Bottom Intake Racks

Water ◽  
2018 ◽  
Vol 10 (8) ◽  
pp. 1035 ◽  
Author(s):  
Juan García ◽  
Luis Castillo ◽  
José Carrillo ◽  
Patricia Haro
Keyword(s):  
Discharge Coefficient ◽  
Experimental Studies ◽  
Three Dimensional ◽  
Design Parameters ◽  
Incoming Flow ◽  
Viscous Forces ◽  
The Mean ◽  
Definition Of ◽  
New Formulation ◽  
Bottom Intake

Flow over bottom racks is highly turbulent, three-dimensional and spatially varied. The design of bottom intake systems has mainly been studied in the laboratory. The comparison of existing experimental studies shows large deviations in the definition of design parameters such as wetted rack length. Each experimental study is limited to a single bar type or to a low range of void ratios, which makes it difficult to generalize the observed data. A combination of empirical, dimensional and inspectional analysis is presented as a useful tool to reduce the number of variables with influence in the design parameters, such as the wetted rack length or the mean discharge coefficient. This work includes a broad experimental campaign in which wetted rack length and mean discharge coefficient are characterized using five different bottom racks with different void ratios (area between bars divided by total area). T-shaped flat and circular bars are considered as well as five different longitudinal slopes. Empirical and inspectional analyses have allowed us to verify, in two different ways, the relation between wetted rack length and incoming flow through potential functions. The influence of the viscous forces has been studied as a function of the incoming flow. Similar results may be obtained when analysing the Froude number at the beginning of the rack, depending on the wetted rack length. A new formulation for calculating the mean discharge coefficient and wetted rack length is proposed.

A Mathematical Analysis of Directional Solidification of Aqueous Solutions

2019 ◽  
Vol 142 (2) ◽  
Author(s):  
Gideon Ukpai ◽  
Boris Rubinsky
Keyword(s):  
Mathematical Model ◽  
Aqueous Solutions ◽  
Mathematical Models ◽  
Directional Solidification ◽  
Experimental Studies ◽  
Three Dimensional ◽  
Design Parameters ◽  
Fundamental Study ◽  
Biological Matter ◽  
Intent To Use

Abstract Horizontal directional solidification techniques have been broadly utilized for the freezing of biological matter under conditions in which the freezing rate during solidification must be controlled and known. Directional solidification is used for diverse applications such as fundamental research on freezing of biological materials, cryopreservation of biological matter, and tissue engineering. This study is motivated by our intent to use directional solidification as a simplified model for the study of three-dimensional (3D) cryoprinting. In evaluating directional solidification in the context of 3D cryoprinting, we realized that current mathematical models of directional solidification are not adequately representative for this purpose, because they are simplified and one-dimensional (1D). Here, we introduce an experimentally verified and more representative two-dimensional (2D) mathematical model of directional solidification that can aid in the fundamental study of freezing of biological matter, in particular during 3D cryoprinting. The mathematical model was used to develop correlations between the freezing rates that a layer of an aqueous solution experiences during directional solidification and the various design parameters such as thickness of the sample and temperature gradients in the substrate. Results show that the freezing rates can be higher than those suggested by the previously used simplified 1D mathematical models. The results can be used for developing simplified models of 3D cryoprinting. In addition, the results suggest that many experimental studies on directional solidification of aqueous solutions and biological matter may require readjustment of analysis, in view of these findings.

Vortical structures in the near wake of tabs with various geometries

2017 ◽  
Vol 825 ◽  
pp. 167-188 ◽  
Author(s):  
A. M. Hamed ◽  
A. Pagan-Vazquez ◽  
D. Khovalyg ◽  
Z. Zhang ◽  
L. P. Chamorro
Keyword(s):  
Large Scale ◽  
Three Dimensional ◽  
Three Dimensions ◽  
Incoming Flow ◽  
Mean Flow ◽  
Near Wake ◽  
Hairpin Vortices ◽  
Vortical Structures ◽  
The Mean ◽  
Hairpin Structures

The vortical structures and turbulence statistics in the near wake of rectangular, trapezoidal, triangular and ellipsoidal tabs were experimentally studied in a refractive-index-matching channel. The tabs share the same bulk dimensions, including a 17 mm height, a 28 mm base width and a $24.5^{\circ }$ inclination angle. Measurements were performed at two Reynolds numbers based on the tab height, $Re_{h}\simeq 2000$ (laminar incoming flow) and 13 000 (turbulent incoming flow). Three-dimensional, three-component particle image velocimetry (PIV) was used to study the mean flow distribution and dominant large-scale vortices, while complementary high-spatial-resolution planar PIV measurements were used to quantify high-order statistics. Instantaneous three-dimensional fields revealed the coexistence of a coherent counter-rotating vortex pair (CVP) and hairpin structures. The CVP and hairpin vortices (the primary structures) exhibit distinctive characteristics and strength across $Re_{h}$ and tab geometries. The CVP is coherently present in the mean flow field and grows in strength over a significantly longer distance at the low $Re_{h}$ due to the lower turbulence levels and the delayed shedding of the hairpin vortices. These features at the low $Re_{h}$ are associated with the presence of Kelvin–Helmholtz instability that develops over three tab heights downstream of the trailing edge. Moreover, a secondary CVP with an opposite sense of rotation resides below the primary one for the four tabs at the low $Re_{h}$. The interaction between the hairpin structures and the primary CVP is experimentally measured in three dimensions and shows complex coexistence. Although the CVP undergoes deformation and splitting at times, it maintains its presence and leads to significant mean spanwise and wall-normal flows.

scholarly journals Residual fuel atomization process simulation

2017 ◽  
Vol 169 (2) ◽  
pp. 108-112
Author(s):  
Oleh KLYUS ◽  
Nadezhda ZAMIATINA
Keyword(s):  
Environmental Performance ◽  
Droplet Diameter ◽  
Combustion Process ◽  
Experimental Studies ◽  
Jet Fuel ◽  
Compression Ignition ◽  
Atomization Process ◽  
Fuel Atomization ◽  
The Mean ◽  
Definition Of

The process of atomization of fuel in engines with compression ignition is determining in organization of the combustion process, the result of which are the economic and environmental performance of the engine. One of the main parameters of the spray jet fuel is the mean droplet diameter. The article presents the results of analytical and experimental studies by the definition of mean diameter of Sauter droplet of atomized residual fuel IFO380.

Feasibility of Shape Memory Alloy Wire Actuation for an Active Steerable Cannula

2015 ◽  
Vol 9 (2) ◽  
Author(s):  
Bardia Konh ◽  
Naresh V. Datla ◽  
Parsaoran Hutapea
Keyword(s):  
Shape Memory Alloy ◽  
Shape Memory ◽  
Breast Biopsy ◽  
Experimental Studies ◽  
Three Dimensional ◽  
Needle Insertion ◽  
Design Parameters ◽  
Fe Model ◽  
In Series ◽  
Steerable Cannula

Needle insertion is used in many diagnostic and therapeutic percutaneous medical procedures such as brachytherapy, thermal ablations, and breast biopsy. Insufficient accuracy using conventional surgical cannulas motivated researchers to provide actuation forces to the cannula's body for compensating the possible errors of surgeons/physicians. In this study, we present the feasibility of using shape memory alloy (SMA) wires as actuators for an active steerable surgical cannula. A three-dimensional (3D) finite element (FE) model of the active steerable cannula was developed to demonstrate the feasibility of using SMA wires as actuators to bend the surgical cannula. The material characteristics of SMAs were simulated by defining multilinear elastic isothermal stress–strain curves that were generated through a matlab code based on the Brinson model. Rigorous experiments with SMA wires were done to determine the material properties as well as to show the capability of the code to predict a stabilized SMA transformation behavior with sufficient accuracy. In the FE simulation, birth and death method was used to achieve the prestrain condition on SMA wire prior to actuation. This numerical simulation was validated with cannula deflection experiments with developed prototypes of the active cannula. Several design parameters affecting the cannula's deflection such as the cannula's Young's modulus, the SMA's prestrain, and its offset from the neutral axis of the cannula were studied using the FE model. Real-time experiments with different prototypes showed that the quickest response and the maximum deflection were achieved by the cannula with two sections of actuation compared to a single section of actuation. The numerical and experimental studies showed that a highly maneuverable active cannulas can be achieved using the actuation of multiple SMA wires in series.

Characteristics of Discharge Coefficient in a Rotating Disk System

1999 ◽  
Vol 121 (4) ◽  
pp. 663-669 ◽  
Author(s):  
D. J. Maeng ◽  
J. S. Lee ◽  
R. Jakoby ◽  
S. Kim ◽  
S. Wittig
Keyword(s):  
Discharge Coefficient ◽  
Three Dimensional ◽  
Compressibility Factor ◽  
Rotating Disk ◽  
Operating Conditions ◽  
Disk System ◽  
Rotating System ◽  
Rotor Disk ◽  
Discharge Behavior ◽  
Definition Of

The discharge coefficient of a long orifice in a rotating system is measured to examine the rotational effect on discharge behavior. The rotating system is comprised of a rotating disk and two stators on both sides of the rotating disk. Test rig is constructed to simulate the real turbine operating conditions. Pressure ratios between upstream and downstream cavities of the orifice range from 1.05 to 1.8, and rotational speed of the rotor disk is varied up to 10,000 rpm. The orifice hole bored through the rotor disk has length-to-diameter ratio of 10. For a better interpretation of discharge behavior, three-dimensional velocity field in the downstream and upstream cavities of the rotor is measured using a Laser Doppler Velocimetry. A new definition of the rotational discharge coefficient is introduced to consider the momentum transfer from the rotor to the orifice flow. Additional loss in the discharge coefficient due to pressure loss in the orifice hole at the inlet and exit regions is quantitatively presented in terms of the Rotation number and the compressibility factor. The effect of corner radiusing at the orifice inlet is also investigated at various rotational conditions.

Three-dimensional flow structures in laminar falling liquid films

2014 ◽  
Vol 743 ◽  
pp. 75-123 ◽  
Author(s):  
Georg F. Dietze ◽  
W. Rohlfs ◽  
K. Nährich ◽  
R. Kneer ◽  
B. Scheid
Keyword(s):  
Surface Waves ◽  
Stokes Equations ◽  
Experimental Studies ◽  
Three Dimensional ◽  
Liquid Films ◽  
Capillary Waves ◽  
Flow Structures ◽  
Two Dimensional ◽  
Viscous Forces ◽  
Falling Liquid Films

AbstractFull numerical simulations of the Navier–Stokes equations for four cases of vertically falling liquid films with three-dimensional surface waves have been performed. Flow conditions are based on several previous experimental studies where the streamwise and spanwise wavelengths were imposed, which we exploit by simulating periodic wave segments. The considered flows are laminar but approach conditions at which intermittent wave-induced turbulence has been observed elsewhere. Working liquids range from water to silicone oil and cover a large interval of the Kapitza number ($\textit {Ka}=18\mbox{--}3923$), which relates capillary to viscous forces. Simulations were performed on a supercomputer, using a finite-volume code and the volume of fluid and continuum surface force methods to account for the multiphase nature of the flow. Our results show that surface waves, consisting of large horseshoe-shaped wave humps concentrating most of the liquid and preceded by capillary ripples on a thin residual film, segregate the flow field into two regions: an inertia-dominated one in the large humps, where the local Reynolds number is up to five times larger than its mean value, and a visco-capillary region, where capillary and/or viscous forces dominate. In the inertial region, an intricate structure of different-scale vortices arises, which is more complicated than film thickness variations there suggest. Conversely, the flow in the visco-capillary region of large-$\textit {Ka} $ fluids is entirely governed by the local free-surface curvature through the action of capillary forces, which impose the pressure distribution in the liquid film. This results in flow separation zones underneath the capillary troughs and a spanwise cellular flow pattern in the region of capillary wave interference. In some cases, capillary waves bridge the large horseshoe humps in the spanwise direction, coupling the two aforementioned regions and leading the flow to oscillate between three- and two-dimensional wave patterns. This persists over long times, as we show by simulations with the low-dimensional model of Scheid et al. (J. Fluid Mech., vol. 562, 2006, pp. 183–222) after satisfactory comparison with our direct simulations at short times. The governing mechanism is connected to the bridging capillary waves, which drain liquid from the horseshoe humps, decreasing their amplitude and wave speed and causing them to retract in the streamwise direction. Overall, it is observed that spanwise flow structures (not accounted for in two-dimensional investigations) are particularly complex due to the absence of gravity in this direction.

scholarly journals Characteristics of Discharge Coefficient in a Rotating Disk System

1998 ◽  
Author(s):  
D. J. Maeng ◽  
J. S. Lee ◽  
R. Jakoby ◽  
S. Kim ◽  
S. Wittig
Keyword(s):  
Discharge Coefficient ◽  
Three Dimensional ◽  
Compressibility Factor ◽  
Rotating Disk ◽  
Operating Conditions ◽  
Disk System ◽  
Rotating System ◽  
Rotor Disk ◽  
Discharge Behavior ◽  
Definition Of

The discharge coefficient of a long orifice in a rotating system is measured to examine the rotational effect on discharge behavior. The rotating system is comprised of a rotating disk and two stators on both sides of the rotating disk. Test rig is constructed to simulate the real turbine operating conditions. Pressure ratios between upstream and downstream cavities of the orifice range from 1.05 to 1.8, and rotational speed of the rotor disk is varied up to 10,000 rpm. The orifice hole bored through the rotor disk has length-to-diameter ratio of 10. For a better interpretation of discharge behavior, three-dimensional velocity field in the downstream and upstream cavities of the rotor is measured using a Laser Doppler Velocimetry. A new definition of the rotational discharge coefficient is introduced to consider the momentum transfer from the rotor to the orifice flow. Additional loss in the discharge coefficient due to pressure loss in the orifice hole at the inlet and exit regions is quantitatively presented in terms of the Rotation number and the compressibility factor. The effect of comer radiusing at the orifice inlet is also investigated at various rotational conditions.

Three-Dimensional Unsteady Simulation of Cavitating Flows in Injector Passages

1999 ◽  
Vol 122 (4) ◽  
pp. 791-797 ◽  
Author(s):  
R. A. Bunnell ◽  
S. D. Heister
Keyword(s):  
Discharge Coefficient ◽  
Three Dimensional ◽  
Exit Plane ◽  
Cavitating Flows ◽  
Discharge Characteristics ◽  
Unsteady Simulation ◽  
The Mean ◽  
Liquid Rocket ◽  
Vorticity Transport

Fully 3-D, unsteady, viscous simulations are performed on a plain-orifice pressure atomizer being fed by a manifold with a crossflow. This geometry replicates features present in both liquid rocket and diesel engine injectors. Both noncavitating and cavitating conditions are considered to determine the role of cavitation on the orifice discharge characteristics. The presence of cavitation is shown to affect both the mean and unsteady components of the orifice discharge coefficient. The presence of a significant cavitation zone can inhibit vorticity transport causing nearly all the fluid to be ejected through a crescent-shaped sector of the orifice exit plane. [S0098-2202(00)01604-7]

scholarly journals Three-dimensional numerical simulation of flow in vertical slot fishways: validation of the model and characterization of the flow

RBRH ◽  
2019 ◽  
Vol 24 ◽  
Author(s):  
Daniela Guzzon Sanagiotto ◽  
Júlia Brusso Rossi ◽  
Luísa Lüdtke Lauffer ◽  
Juan Martín Bravo
Keyword(s):  
Numerical Simulation ◽  
Computational Cost ◽  
Experimental Studies ◽  
Three Dimensional ◽  
Maximum Flow ◽  
Mean Value ◽  
Vertical Slot ◽  
Longitudinal Slope ◽  
The Mean

ABSTRACT Vertical slot fishways allow energy dissipation as a function of the pool, longitudinal slope, baffle and vertical slot design. The mean and turbulent flow patterns in these structures must be compatible with the fish target. The design of these structures is commonly based on previous successful fishways as well as simplified theoretical equations and empirical relationships. To aid in the design of these structures, a three-dimensional hydrodynamic model was used to simulate the flow, and experimental studies were used to validate the model. The mean velocities, pressures and parameters indicative of turbulence were analyzed. The maximum flow velocities were up to 32% higher than the values obtained using a simplified theoretical equation. The evaluation of the volumetric dissipated power indicated that the mean value for the pool was lower than 150 W/m3; however, analysis of the spatial distribution showed that in some areas, the values can exceed 1000 W/m3. The results indicate that the numerical simulation was able to adequately represent the flow considering the computational cost involved. Accordingly, it can be used as a complementary tool for the design of new fishways and for the analysis of modifications in existing ones.

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