scholarly journals Experimental Investigation of the Flow Field in the Vicinity of an Oscillating Wave Surge Converter

2020 ◽  
Vol 8 (12) ◽  
pp. 976
Author(s):  
Moisés Brito ◽  
Rui M. L. Ferreira ◽  
Luis Teixeira ◽  
Maria G. Neves ◽  
Luís Gil
Keyword(s):  
Experimental Data ◽  
Boundary Layer ◽  
Mass Transfer ◽  
Flow Field ◽  
Nonlinear Behavior ◽  
Front Face ◽  
Regular Wave ◽  
Turbulent Field ◽  
Analytical Results ◽  
Power Capture

The main objective of this paper is to characterize the flow field on the front face of an oscillating wave surge converter (OWSC) under a regular wave. For this purpose, the longitudinal and vertical velocity components were measured using an Ultrasonic Velocity Profiler (UVP). In order to explain the main trends of the OWSC’s dynamics, the experimental data were firstly compared with the analytical results of potential theory. A large discrepancy was observed between experimental and analytical results, caused by the nonlinear behavior of wave-OWSC interaction that determine the turbulent field and the boundary layer. The experimental velocity field shows a strong ascendant flow generated by the mass transfer over the flap (overtopping) and flow rotation generated by the beginning of the flap deceleration and acceleration. These features (overtopping and flow rotation) have an important role on the power capture of OWSC and, therefore, analytical results are not accurate to describe the complex hydrodynamics of OWSC.

Time Scales for Unsteady Mass Transfer From a Sphere at Low-Finite Reynolds Numbers

2003 ◽  
Vol 125 (4) ◽  
pp. 716-723 ◽  
Author(s):  
Stanley J. Kleis ◽  
Ivan Rivera-Solorio
Keyword(s):  
Boundary Layer ◽  
Mass Transfer ◽  
Flow Field ◽  
Time Scales ◽  
Free Stream ◽  
Reynolds Numbers ◽  
Concentration Boundary Layer ◽  
Concentration Boundary ◽  
Boundary Layer Development ◽  
Layer Development

The problem of unsteady mass transfer from a sphere that impulsively moves from rest to a finite velocity in a non-uniform concentration distribution is studied. A range of low Reynolds numbers (Re<1) and moderate Peclet numbers (Pe ranges from 5.6 to 300) is investigated (typical of the parameters encountered in anchorage dependent cell cultures in micro gravity). Using time scales, the effects of flow field development, concentration boundary layer development and free stream concentration variation are investigated. For the range of parameters considered, the development of the flow field has a negligible effect on the time variation of the Sherwood number (Sh). The Sh time dependence is dominated by concentration boundary layer development for early times and free stream concentration variations at later times.

scholarly journals DNS of a turbulent boundary layer using inflow conditions derived from 4D-PTV data

2021 ◽  
Vol 62 (9) ◽  
Author(s):  
Jason Appelbaum ◽  
Duncan Ohno ◽  
Ulrich Rist ◽  
Christoph Wenzel
Keyword(s):  
Experimental Data ◽  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Flow Field ◽  
Nearest Neighbor ◽  
Tracer Particle ◽  
Flow Analysis ◽  
Mean Flow ◽  
Experimental Field ◽  
Inlet Region

AbstractUnsteady, 3D particle tracking velocimetry (PTV) data are applied as an inlet boundary condition in a direct numerical simulation (DNS). The considered flow case is a zero pressure gradient (ZPG) turbulent boundary layer (TBL) flow over a flat plate. The study investigates the agreement between the experimentally measured flow field and its simulated counterpart with a hybrid 3D inlet region. The DNS field inherits a diminishing contribution from the experimental field within the 3D inlet region, after which it is free to spatially evolve. Since the measurement does not necessarily provide a spectrally complete description of the turbulent field, the spectral recovery of the flow field is analyzed as the TBL evolves. The study summarizes the pre-processing methodology used to bring the experimental data into a form usable by the DNS as well as the numerical method used for simulation. Spectral and mean flow analysis of the DNS results show that turbulent structures with a characteristic length on the order of one average tracer particle nearest neighbor radius $${\bar{r}}_{\text {NN}}$$ r ¯ NN or greater are well reproduced and stay correlated to the experimental field downstream of the hybrid inlet. For turbulent scales smaller than $${\bar{r}}_{\text {NN}}$$ r ¯ NN , where experimental data are sparse, a relatively quick redevelopment of previously unresolved turbulent energy is seen. The results of the study indicate applicability of the approach to future DNS studies in which specific upstream or far field boundary conditions (BCs) are required and may provide the utility of decreasing high initialization costs associated with conventional inlet BCs. Graphic abstract

A contribution to the problem of turbulent mass transfer at high values of the Schmidt number and to the hydrodynamics of the turbulent boundary layer

1986 ◽  
Vol 51 (1) ◽  
pp. 75-80 ◽  
Author(s):  
Václav Kolář ◽  
František Vašák ◽  
Zdeněk Brož
Keyword(s):  
Experimental Data ◽  
Boundary Layer ◽  
Mass Transfer ◽  
Turbulent Boundary Layer ◽  
Transition Layer ◽  
Schmidt Number ◽  
Interface Parameters ◽  
Turbulent Mass Transfer

It has been shown in the paper that under the turbulence (Re > 104) and at high values of the Schmidt number (Sc > 103), when the principal resistance to mass transfer is concentrated in the laminar layer immediately adhering to the interface, significant instabilities appear induced by the turbulent disturbances in the neighbouring transition layer, or by the discontinuities at the interface. Parameters have been determined characterizing this phenomenon on the basis of experimental data and their values have been compared with the data published in the literature as characteristics of the periodic viscous sublayers.

Temperature Scalings and Profiles in Forced Convection Turbulent Boundary Layers

2008 ◽  
Vol 130 (2) ◽  
Author(s):  
Xia Wang ◽  
Luciano Castillo ◽  
Guillermo Araya
Keyword(s):  
Experimental Data ◽  
Boundary Layer ◽  
Mass Transfer ◽  
Pressure Gradient ◽  
Temperature Profile ◽  
Forced Convection ◽  
Boundary Layers ◽  
Heat Mass Transfer ◽  
Turbulent Boundary Layers ◽  
Similarity Analysis

Based on the theory of similarity analysis and the analogy between momentum and energy transport equations, the temperature scalings have been derived for forced convection turbulent boundary layers. These scalings are shown to be able to remove the effects of Reynolds number and the pressure gradient on the temperature profile. Furthermore, using the near-asymptotic method and the scalings from the similarity analysis, a power law solution is obtained for the temperature profile in the overlap region. Subsequently, a composite temperature profile is found by further introducing the functions in the wake region and in the near-the-wall region. The proposed composite temperature profile can describe the entire boundary layer from the wall all the way to the outer edge of the turbulent boundary layer at finite Re number. The experimental data and direct numerical simulation (DNS) data with zero pressure gradient and adverse pressure gradient are used to confirm the accuracy of the scalings and the proposed composite temperature profiles. Comparison with the theoretical profiles by Kader (1981, “Temperature and Concentration Profiles in Fully Turbulent Boundary Layers,” Int. J. Heat Mass Transfer, 24, pp. 1541–1544; 1991, “Heat and Mass Transfer in Pressure-Gradient Boundary Layers,” Int. J. Heat Mass Transfer, 34, pp. 2837–2857) shows that the current theory yields a higher accuracy. The error in the mean temperature profile is within 5% when the present theory is compared to the experimental data. Meanwhile, the Stanton number is calculated using the energy and momentum integral equations and the newly proposed composite temperature profile. The calculated Stanton number is consistent with previous experimental results and the DNS data, and the error of the present prediction is less than 5%. In addition, the growth of the thermal boundary layer is obtained from the theory and the average error is less than 5% for the range of Reynolds numbers between 5×105 and 5×106 when compared with the empirical correlation for the experimental data of isothermal boundary layer conditions.

Simulation Study on the Characteristics of Flow Field in the Process of Wave Impact

2012 ◽  
Vol 212-213 ◽  
pp. 1172-1176
Author(s):  
Jin Feng
Keyword(s):  
Experimental Data ◽  
Free Surface ◽  
Flow Field ◽  
Simulation Study ◽  
Numerical Models ◽  
Two Dimensional ◽  
Regular Wave ◽  
Wave Impact ◽  
Distribution Rule ◽  
Wave Slamming

In order to study the characteristics of flow field in the process of wave impact, two-dimensional regular wave numerical models were established based on the software FLUENT. RANS equations were adopted. The standard equations were used to close the Reynolds equations. VOF method was used to reconstruct the free surface. After three typical cases of wave slamming on open-piled structures were reproduced, the models were verified by experimental data and the flow field surrounding the structure was displayed visually. Then the processes of wave impact under various wave height, period and over height were simulated. The influences of the three parameters on the distribution of vertical velocities were analyzed, which shows that the distribution rule of the vertical velocities is similar to the wave impact pressures.

Flow field decomposition applied to experimental data obtained for a transitional boundary layer

1996 ◽  
Vol 56 (2-3) ◽  
pp. 103-112 ◽  
Author(s):  
M. Fischer ◽  
M. Wiegel ◽  
T. Herberg ◽  
G. Heiderich
Keyword(s):  
Experimental Data ◽  
Boundary Layer ◽  
Flow Field ◽  
Transitional Boundary Layer

An Interferometric Study of Mass Transfer From a Vertical Plate at Low Reynolds Numbers

1966 ◽  
Vol 88 (4) ◽  
pp. 399-406 ◽  
Author(s):  
M. M. El-Wakil ◽  
G. E. Myers ◽  
R. J. Schilling
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Boundary Layer ◽  
Mass Transfer ◽  
Natural Convection ◽  
Free Convection ◽  
Forced Convection ◽  
Boundary Layers ◽  
Reynolds Numbers ◽  
Perturbation Solutions

Experimental concentration profiles in steady-state, two-component boundary layers formed by the evaporation of a volatile liquid from a porous vertical flat plate into a heated airstream were obtained by an interferometric technique. Tests were conducted with benzene and n-heptane as the evaporating fluids with airstream temperatures ranging from 70 to 94 F and airstream velocities ranging from 90 to 120 fpm. The Reynolds number range, based on the distance from the leading edge of the plate, was from 75 to 1800. It was experimentally observed that transition from laminar flow occurred at Reynolds numbers between 300 and 600. These values, much lower than generally reported in the literature for heat transfer alone, are believed to be related to the relatively thick boundary layers induced by mass transfer of the heavier-than-air fluid from the plate and the associated free-convection effects. While the flow was primarily forced convection, the experimental data indicated a strong natural-convection effect when compared with analytical predictions based on forced convection alone. This was due primarily to the mass transfer into the boundary layer. An attempt was made to analytically account for the effects of mass transfer and natural convection on the Sherwood-Reynolds numbers relationship by utilizing perturbation solutions for the analogous heat transfer problem. The trends shown by this analysis agreed with the experimental data in the laminar portion of the boundary layer. The absolute magnitudes, however, still differed significantly, showing that first-order perturbation solutions of the mass transfer and free-convection effects are inadequate and pointing to the need for more theoretical work.

Mass Transfer Considerations in the Design of Vapor-Phase photocatalytic Reactors

1998 ◽  
Vol 3 (2) ◽  
Author(s):  
Ali Τ- Raissi ◽  
Eric D. Martin ◽  
Sivakumar Jaganathan
Keyword(s):  
Fluid Dynamics ◽  
Experimental Data ◽  
Mass Transfer ◽  
Computational Fluid Dynamics ◽  
Flow Field ◽  
Vapor Phase ◽  
Flow Reactor ◽  
Scale Up ◽  
Computational Techniques ◽  
Photocatalytic Reactors

AbstractAs the bench-scale photoreactors are upscaled to progressively larger units, heat and mass transfer considerations become increasingly important. Powerful analytical and computational techniques are available to augment experimental data and aid process optimization and scale up. In this paper, the analytical and computational techniques available for the design of vapor-phase photocatalytic reactors are discussed. First, the Graetz- Nusselt-Leveque problem in annuli is analyzed and its application to the design of the photocatalytic reactors described. Then, the analytical predications are compared to experimental flow reactor data. Finally, results from a Computational Fluid Dynamics program simulating a flow field within an annular baffled photoreactor are given and discussed. These techniques are particularly useful as they simplify the design and scale-up of vapor-phase photocatalytic reactors.

Aerodynamic Behaviour of a Novel Three-Dimensional Shaped Transonic Compressor Rotor Blade

2008 ◽  
Author(s):  
Roberto Biollo ◽  
Ernesto Benini
Keyword(s):  
Experimental Data ◽  
Boundary Layer ◽  
Numerical Model ◽  
Flow Field ◽  
Mass Flow ◽  
Three Dimensional ◽  
Tip Clearance ◽  
Stall Margin ◽  
Layer Interaction ◽  
Boundary Layer Interaction

This paper compares the aerodynamic behaviour of baseline and redesigned versions of the well-known NASA Rotor 37. The aerodynamic behaviour of the two rotors was evaluated using an accurate and validated 3-D CFD RANS model. The redesigned version showed both higher efficiency and wider stall margin. The new rotor was modeled by giving to the radial stacking line of baseline blade a three-dimensional shape. The blade was curved mainly toward the direction of rotor rotation. The applied blade curvature comes from previous personal investigations on the effects of stacking line shape in transonic bladings. Steady-state simulations were carried out to calculate the flow field inside the two rotors. The numerical model was developed using a commercial CFD code. The code was validated by simulating the Rotor 37 and comparing the computed results to the experimental data available in the open literature. The validation process gave a satisfactory agreement between predictions and measurements, showing that the overall features of the three-dimensional shock structure, shock-boundary layer interaction and tip clearance flows are calculated well in the numerical solution. With respect to the baseline rotor, the redesigned version gave a higher efficiency in a large part of the operating range, with a maximum increment of about 1.2 percentage points around the peak efficiency condition. The improvements in efficiency can be associated with a less detrimental shock-blade boundary layer interaction at the outer span, probably due to the different three-dimensional shock structure developed. At the outer span, in fact, the new blade showed a blade-to-blade shock front more oblique than in the baseline rotor. Further, the new blade positively impacted the flow field near the casing at low flow operating conditions. A less detrimental shock-tip clearance vortex-boundary layer interaction, along with a considerable reduction of the low momentum fluid region after the shock, was observed. CFD flow visualizations showed clearly a higher stall margin. The last stable operating point provided by the numerical model implemented gave a normalized mass flow of about 92% in the case of Rotor 37 (in accordance with experimental data) and about 90% in the case of redesigned version. The two rotors showed a similar choking mass flow rate.

Laminar Boundary Layer Development Around a Circular Cylinder: Fluid Flow and Heat-Mass Transfer Characteristics

2010 ◽  
Vol 132 (12) ◽  
Author(s):  
A. Alper Ozalp ◽  
Ibrahim Dincer
Keyword(s):  
Boundary Layer ◽  
Mass Transfer ◽  
Circular Cylinder ◽  
Moisture Diffusivity ◽  
Front Face ◽  
Cylinder Surface ◽  
Transfer Coefficients ◽  
Mass Transfer Coefficients ◽  
Practical Applications ◽  
Transfer Characteristics

This paper presents a comprehensive computational work on the hydrodynamic, thermal, and mass transfer characteristics of a circular cylinder, subjected to confined flow at the cylinder Reynolds number of Red=40. As the two-dimensional, steady and incompressible momentum and energy equations are solved using ANSYS-CFX (version 11.0), the moisture distributions are computed by a new alternating direction implicit method based software. The significant results, highlighting the influence of blockage (β=0.200–0.800) on the flow and heat transfer mechanism and clarifying the combined roles of β and moisture diffusivity (D=1×10−8–1×10−5 m2/s) on the mass transfer behavior, are obtained for practical applications. It is shown that the blockage augments the friction coefficients (Cf) and Nusselt numbers (Nu) on the complete cylinder surface, where the average Nu are evaluated as Nuave=3.66, 4.05, 4.97, and 6.51 for β=0.200, 0.333, 0.571, and 0.800. Moreover, the blockage shifts separation (θs) and maximum Cf locations (θCf−max) downstream to the positions of θs=54.10, 50.20, 41.98, and 37.30 deg and θCf−max=51.5, 53.4, 74.9, and 85.4 deg. The highest blockage of β=0.800 encourages the downstream backward velocity values, which as a consequence disturbs the boundary layer and weakens the fluid-solid contact. The center and average moisture contents differ significantly at the beginning of drying process, but in the last 5% of the drying period they vary only by 1.6%. Additionally, higher blockage augments mass transfer coefficients (hm) on the overall cylinder surface; however, the growing rate of back face mass transfer coefficients (hm−bf) is dominant to that of the front face values (hm−ff), with the interpreting ratios of h¯m−bf/h¯m=0.50 and 0.57 and h¯m−ff/h¯m=1.50 and 1.43 for β=0.200 and 0.800.

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