The three-dimensional hydrodynamics of tadpole locomotion.

1997 ◽  
Vol 200 (22) ◽  
pp. 2807-2819 ◽  
Author(s):  
H Liu ◽  
R Wassersug ◽  
K Kawachi
Keyword(s):  
Unsteady Flow ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Small Region ◽  
High Amplitude ◽  
Three Dimensions ◽  
Cfd Model ◽  
Hind Limbs ◽  
Lower Amplitude ◽  
Low Efficiency

Tadpoles are unusual among vertebrates in having a globose body with a laterally compressed tail abruptly appended to it. Compared with most teleost fishes, tadpoles swim awkwardly, with waves of relatively high amplitude at both the snout and tail tip. In the present study, we analyze tadpole propulsion using a three-dimensional (3D) computational fluid dynamic (CFD) model of undulatory locomotion that simulates viscous and unsteady flow around an oscillating body of arbitrary 3D geometry. We first confirm results from a previous two-dimensional (2D) study, which suggested that the characteristic shape of tadpoles was closely matched to their unusual kinematics. Specifically, our 3D results reveal that the shape and kinematics of tadpoles collectively produce a small 'dead water' zone between the head-body and tail during swimming precisely where tadpoles can and do grow hind limbs--without those limbs obstructing flow. We next use our CFD model to show that 3D hydrodynamic effects (cross flows) are largely constrained to a small region along the edge of the tail fin. Although this 3D study confirms most of the results of the 2D study, it shows that propulsive (Froude) efficiency for tadpoles is overall lower than predicted from a 2D analysis. This low efficiency is not, however, a result of the high-amplitude undulations of the tadpole. This was demonstrated by forcing our 'virtual' tadpole to swim with fish-like kinematics, i.e. with lower-amplitude propulsive waves. That particular simulation yielded a much lower Froude efficiency, confirming that the large-amplitude lateral oscillations of the tadpole do, indeed, provide positive thrust. This, we believe, is the first time that the unsteady flow generated by an undulating vertebrate has been realistically modelled in three dimensions. Our study demonstrates the feasibility of using 3D CFD methods to model the locomotion of other undulatory organisms.

Paper 18: Fluid Dynamic Aspects of Unsteady Flow in Branched Ducts

1967 ◽  
Vol 182 (8) ◽  
pp. 167-174 ◽  
Author(s):  
B. E. L. Deckker ◽  
D. H. Male
Keyword(s):  
Boundary Conditions ◽  
Unsteady Flow ◽  
Fluid Dynamic ◽  
High Amplitude ◽  
Quantitative Information ◽  
Schlieren Method ◽  
Pressure Losses ◽  
Static Pressure Distribution ◽  
Flow Through ◽  
Hydraulic Analogy

Unsteady flow through three-branched pipe configurations has been investigated with the object of finding boundary conditions suitable for use in the analysis of high-amplitude waves using the method of characteristics. The schlieren method and the hydraulic analogy were used to obtain qualitative information about the quasi-steady flow patterns. Quantitative information concerning these patterns was obtained by the measurement of stagnation pressure losses and of the static pressure distribution. Several methods of deriving boundary conditions have been reviewed, and it is considered that those obtained directly by experiment are the most convenient to use.

scholarly journals Experimental Analysis and CFD Modeling for Conventional Basin-Type Solar Still

Energies ◽  
2020 ◽  
Vol 13 (21) ◽  
pp. 5734
Author(s):  
Mahmoud S. El-Sebaey ◽  
Asko Ellman ◽  
Ahmed Hegazy ◽  
Tarek Ghonim
Keyword(s):  
Fresh Water ◽  
Water Depth ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Cfd Modeling ◽  
Solar Still ◽  
Cfd Model ◽  
Climate Conditions ◽  
Experimental Values ◽  
Multi Phase

With the rising population, environmental pollution, and social development, potable water is reducing and being contaminated day by day continually. Thus, several researchers have focused their studies on seas and oceans in order to get potable fresh water by desalination of their saltwater. Solar still of basin type is one of the available technologies to purify water because of free solar energy. The computational fluid dynamic CFD model of the solar still can significantly improve means for optimization of the solar still structure because it reduces the need for conducting large amount of experiments. Therefore, the main purpose of this study is presenting a multi-phase, three-dimensional CFD model, which predicts the performance of the solar still without using any experimental measurements, depending on the CFD solar radiation model. Simulated results are compared with experimental values of water and glass cover temperatures and yield of fresh water in climate conditions of Sheben El-Kom, Egypt (latitude 30.5° N and longitude 31.01° E). The simulation results were found to be in acceptable agreement with the experimental measured data. The results indicated that the daily simulated and experimental accumulated productivities of the single-slope solar still were found to be 1.982 and 1.785 L/m2 at a water depth of 2 cm. In addition, the simulated and experimental daily efficiency were around 16.79% and 15.5%, respectively, for the tested water depth.

Design of fluid components using the topological optimization method

2019 ◽  
Vol 36 (5) ◽  
pp. 1430-1448
Author(s):  
L.C. Ruspini ◽  
E. Dari ◽  
C. Padra ◽  
G.H. Paissan ◽  
N.N. Salva
Keyword(s):  
Stokes Equations ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Optimization Method ◽  
Industrial Applications ◽  
Design Tool ◽  
Three Dimensions ◽  
Topological Optimization ◽  
Engineering Structures ◽  
Content Type

Purpose The purpose of this paper is to present applications of the topological optimization method dealing with fluid dynamic problems in two- and three dimensions. The main goal is to develop a tool package able to optimize topology in realistic devices (e.g. inlet manifolds) considering the non-linear terms on Navier–Stokes equations. Design/methodology/approach Using an in-house Fortran code, a Galerkin stabilized finite element is implemented method to solve the three equation systems necessary for the topological optimization method: the direct problem, adjoint problem and topological derivative. The authors address the non-linearity in the equations using an iterative method. Different techniques to create holes into a two-dimensional discrete domain are analyzed. Findings One technique to create holes produces more accurate and robust results. The authors present several examples of applications in two- and three-dimensional components, which highlight the potential of this method in the optimization of fluid components. Research limitations/implications The authors contribute to the methodology and design in engineering. Practical implications Engineering fluid flow systems are used in many different industrial applications, e.g. oil flow in pipes; air flow around an airplane wing; sailing submarines; blood flow in synthetic arteries; and thermal and fissure spreading problems. The aim of this work is to create an effective design tool for obtaining efficient engineering structures and devices. Originality/value The authors contribute by creating an application of the method to design a tridimensional realistic device, which can be essayed experimentally. Particularly, the authors apply the design tool to an inlet manifold.

scholarly journals NUMERICAL INVESTIGATION OF THE EFFECTS OF GEOMETRICAL PARAMETERS ON THE VORTEX SEPARATION PHENOMENON INSIDE A RANQUE-HILSCH VORTEX TUBE USED AS AN AIR SEPARATOR IN A HELICOPTER’S ENGINE

Aviation ◽  
2018 ◽  
Vol 22 (1) ◽  
pp. 13-23 ◽  
Author(s):  
Adib Bazgir ◽  
Nader Nabhani
Keyword(s):  
Vortex Tube ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Temperature Fields ◽  
Geometrical Parameters ◽  
Cfd Model ◽  
Steady State Condition ◽  
Axial Angle ◽  
Temperature Reduction ◽  
Vortex Separation

Air separators are fitted to helicopter engine intakes to remove potentially harmful dust from the influent air. Their use is necessary in desert environments to eliminate the risk of rapid engine wear and subsequent power deterioration. However, their employment is concomitant with an inherent loss in inlet pressure and, in some cases, auxiliary power. There are three main technologies: vortex tubes, barrier filters, and integrated inlet particle separators. In this work, a vortex tube is investigated numerically. The study was conducted on the number and axial angle of inlet nozzles. Two and three-dimensional models are investigated at a steady state condition then the standard k-ε turbulence model is utilised for determining the flow and temperature fields. The finite volume method base on a Computational Fluid Dynamic (CFD) model is verified through the comparison with experimental data and numerical results of a vortex tube, reported in literature sources. Increasing the number of inlet nozzles, increases the sensitivity of the temperature reduction and the highest possible temperature reduction can be obtained. A vortex tube with an axial angle inlet nozzle of yields better performance. The numerical simulation results indicated that the CFD model is capable of predicting the vortex separation phenomenon inside a Ranque-Hilsch vortex tube with different geometrical parameters.

Linearized Unsteady Viscous Turbomachinery Flows Using Hybrid Grids

2001 ◽  
Vol 123 (3) ◽  
pp. 568-582 ◽  
Author(s):  
L. Sbardella ◽  
M. Imregun
Keyword(s):  
Unsteady Flow ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Two Dimensions ◽  
Three Dimensions ◽  
Laplacian Operator ◽  
Finite Volume Scheme ◽  
Test Case ◽  
Flow Equations ◽  
Mixed Element

The paper describes the theory and the numerical implementation of a three-dimensional finite volume scheme for the solution of the linearized, unsteady Favre-averaged Navier–Stokes equations for turbomachinery applications. A further feature is the use of mixed element grids, consisting of triangles and quadrilaterals in two dimensions, and of tetrahedra, triangular prisms, and hexahedra in three dimensions. The linearized unsteady viscous flow equations are derived by assuming small harmonic perturbations from a steady-state flow and the resulting equations are solved using a pseudo-time marching technique. Such an approach enables the same numerical algorithm to be used for both the nonlinear steady and the linearized unsteady flow computations. The important features of the work are the discretization of the flow domain via a single, unified edge-data structure for mixed element meshes, the use of a Laplacian operator, which results in a nearest neighbor stencil, and the full linearization of the Spalart–Allmaras turbulence model. Four different test cases are presented for the validation of the proposed method. The first one is a comparison against the classical subsonic flat plate cascade theory, the so-called LINSUB benchmark. The aim of the second test case is to check the computational results against the asymptotic analytical solution derived by Lighthill for an unsteady laminar flow. The third test case examines the implications of using inviscid, frozen-turbulence, and fully turbulent models when linearizing the unsteady flow over a transonic turbine blade, the so-called 11th International Standard Configuration. The final test case is a rotor/stator interaction, which not only checks the validity of the formulation for a three-dimensional example, but also highlights other issues, such as the need to linearize the wall functions. Detailed comparisons were carried out against measured steady and unsteady flow data for the last two cases and good overall agreement was obtained.

scholarly journals CFD Investigation of Vehicle’s Ventilation Systems and Analysis of ACH in Typical Airplanes, Cars, and Buses

2021 ◽  
Vol 13 (12) ◽  
pp. 6799
Author(s):  
Behrouz Pirouz ◽  
Domenico Mazzeo ◽  
Stefania Anna Palermo ◽  
Seyed Navid Naghib ◽  
Michele Turco ◽  
...  
Keyword(s):  
Energy Demand ◽  
Infection Prevention ◽  
Fluid Dynamic ◽  
Demand Management ◽  
Three Dimensional ◽  
Hvac Systems ◽  
Cfd Modeling ◽  
Cfd Model ◽  
Cabin Environment

The simulation of the ventilation and the heating, ventilation, and air conditioning (HVAC) systems of vehicles could be used in the energy demand management of vehicles besides improving the air quality inside their cabins. Moreover, traveling by public transport during a pandemic is a concerning factor, and analysis of the vehicle’s cabin environments could demonstrate how to decrease the risk and create a safer journey for passengers. Therefore, this article presents airflow analysis, air changes per hour (ACH), and respiration aerosols’ trajectory inside three vehicles, including a typical car, bus, and airplane. In this regard, three vehicles’ cabin environment boundary conditions and the HVAC systems of the selected vehicles were determined, and three-dimensional numerical simulations were performed using computational fluid dynamic (CFD) modeling. The analysis of the airflow patterns and aerosol trajectories in the selected vehicles demonstrate the critical impact of inflow, outflow, and passenger’s locations in the cabins. The CFD model results exhibited that the lowest risk could be in the airplane and the highest in the bus because of the location of airflows and outflows. The discrete CFD model analysis determined the ACH for a typical car of about 4.3, a typical bus of about 7.5, and in a typical airplane of about 8.5, which were all less than the standard protocol of infection prevention, 12 ACH. According to the results, opening windows in the cars could decrease the aerosol loads and improve the low ACH by the HVAC systems. However, for the buses, a new design for the outflow location or an increase in the number of outflows appeared necessary. In the case of airplanes, the airflow paths were suitable, and by increasing the airflow speed, the required ACH might be achieved. Finally, in the closed (recirculating) systems, the role of filters in decreasing the risk appeared critical.

Research on Windage Power Loss of Spur Gear Base on CFD

2012 ◽  
Vol 184-185 ◽  
pp. 450-455 ◽  
Author(s):  
Ning Zhao ◽  
Qing Jian Jia
Keyword(s):  
Computational Fluid Dynamic ◽  
Power Loss ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Spur Gear ◽  
Cfd Model ◽  
Major Parameter ◽  
Proportional Relationship ◽  
Tooth Flank ◽  
Icem Cfd

The paper established three-dimensional Computational fluid dynamic (CFD) model of the oil-air mixture in the gearbox after meshing by ICEM CFD simulated the turbulence model by the CFD. The method of calculate the windage power loss (WPL) of the spur gear were put forward. In order to reduced the WPL, compared the results between the CFD model with different modulus、clearance of the shroud and radius of the modification of gear top. The modulus is major parameter to WPL; the gear with shroud have lower WPL , WPL of the tooth flank and clearance of the tooth flank shroud do not show the proportional relationship, the gear with smallest clearance of gear side have lowest WPL，the modification of gear top can reduce the eddy scale which can reduce the WPL.

scholarly journals Clap-and-fling mechanism in a hovering insect-like two-winged flapping-wing micro air vehicle

2016 ◽  
Vol 3 (12) ◽  
pp. 160746 ◽  
Author(s):  
Hoang Vu Phan ◽  
Thi Kim Loan Au ◽  
Hoon Cheol Park
Keyword(s):  
Drag Force ◽  
Cfd Simulation ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Flapping Wing ◽  
Micro Air Vehicle ◽  
Force Generation ◽  
Vertical Force ◽  
Cfd Model ◽  
Air Vehicle

This study used numerical and experimental approaches to investigate the role played by the clap-and-fling mechanism in enhancing force generation in hovering insect-like two-winged flapping-wing micro air vehicle (FW-MAV). The flapping mechanism was designed to symmetrically flap wings at a high flapping amplitude of approximately 192°. The clap-and-fling mechanisms were thereby implemented at both dorsal and ventral stroke reversals. A computational fluid dynamic (CFD) model was constructed based on three-dimensional wing kinematics to estimate the force generation, which was validated by the measured forces using a 6-axis load cell. The computed forces proved that the CFD model provided reasonable estimation with differences less than 8%, when compared with the measured forces. The measurement indicated that the clap and flings at both the stroke reversals augmented the average vertical force by 16.2% when compared with the force without the clap-and-fling effect. In the CFD simulation, the clap and flings enhanced the vertical force by 11.5% and horizontal drag force by 18.4%. The observations indicated that both the fling and the clap contributed to the augmented vertical force by 62.6% and 37.4%, respectively, and to the augmented horizontal drag force by 71.7% and 28.3%, respectively. The flow structures suggested that a strong downwash was expelled from the opening gap between the trailing edges during the fling as well as the clap at each stroke reversal. In addition to the fling phases, the influx of air into the low-pressure region between the wings from the leading edges also significantly contributed to augmentation of the vertical force. The study conducted for high Reynolds numbers also confirmed that the effect of the clap and fling was insignificant when the minimum distance between the two wings exceeded 1.2c (c = wing chord). Thus, the clap and flings were successfully implemented in the FW-MAV, and there was a significant improvement in the vertical force.

Three-Dimensional Numerical Modeling of Pier Scour Under Current and Waves Using Level-Set Method

2015 ◽  
Vol 137 (3) ◽  
Author(s):  
Mohammad Saud Afzal ◽  
Hans Bihs ◽  
Arun Kamath ◽  
Øivind A. Arntsen
Keyword(s):  
Free Surface ◽  
Level Set Method ◽  
Level Set ◽  
Three Dimensional ◽  
Three Dimensions ◽  
Navier Stokes ◽  
Reasonable Assumption ◽  
Cfd Model ◽  
Time Step ◽  
Pier Scour

A three-dimensional (3D) computational fluid dynamics (CFD) model is used to calculate the scour and the deposition pattern around a pier for two different boundary conditions: constant discharge and regular waves. The CFD model solves Reynolds-Averaged Navier–Stokes (RANS) equations in all three dimensions. The location of the free-surface is represented using the level-set method (LSM), which calculates the complex motion of the free-surface in a very realistic manner. For the implementation of waves, the CFD code is used as a numerical wave tank. For the geometric representation of the moveable sediment bed, the LSM is used. The numerical results for the local scour prediction are compared with physical experiments. The decoupling of the hydrodynamic and the morphodynamic time step is tested and found to be a reasonable assumption. For the two situations of local pier scour under current and wave conditions, the numerical model predicts the general evolution (geometry, location, and maximum scour depth) and time development of the scour hole accurately.

scholarly journals A novel quantitative analysis method for idiopathic epiretinal membrane

PLoS ONE ◽  
2021 ◽  
Vol 16 (3) ◽  
pp. e0247192
Author(s):  
Davide Allegrini ◽  
Giovanni Montesano ◽  
Stefania Marconi ◽  
Nicoletta Rosso ◽  
Giovanni Ometto ◽  
...  
Keyword(s):  
Visual Acuity ◽  
Epiretinal Membrane ◽  
Three Dimensional ◽  
Small Region ◽  
Posterior Pole ◽  
Three Dimensions ◽  
Dimensional Changes ◽  
Corrected Visual Acuity ◽  
Three Dimensional Measurement ◽  
Best Corrected Visual Acuity

Purpose To introduce a novel method to quantitively analyse in three dimensions traction forces in a vast area of the ocular posterior pole. Methods Retrospective analysis of 14 eyes who underwent peeling surgery for idiopathic, symptomatic and progressive epiretinal membrane. The technique measures the shift in position of vascular crossings after surgery from a fixed point, which is the retinal pigmented epithelium. This shift is defined as the relaxation index (RI) and represents a measure of the postoperative movement of the retina due to released traction after surgery. Results Best-corrected visual acuity was significantly better than baseline at all follow ups while the RI had its maximum value at baseline. Moreover, we found a significant correlation between best-corrected visual acuity at 6 months and RI at baseline. Conclusion While all previous published methods focused on bi-dimensional changes observed in a small region, this study introduces a three-dimensional assessment of tractional forces. Future integration of RI into built-in processing software will allow systematic three-dimensional measurement of intraretinal traction.

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