scholarly journals Numerical investigation of a small water turbine used for the power supply of underwater vehicles

2018 ◽  
Vol 10 (6) ◽  
pp. 168781401878365 ◽  
Author(s):  
Zhaoyong Mao ◽  
Jingang Bai
Keyword(s):  
Stokes Equations ◽  
Underwater Vehicles ◽  
Geometric Parameters ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Sliding Mesh ◽  
Small Water ◽  
Water Turbine ◽  
Computational Fluid Dynamics Simulations ◽  
Dynamics Simulations

The development of underwater vehicles is facing the problem of sustainable energy supply. This study introduces a small water turbine, the Lenz turbine, for energy generation from the ocean currents which will provide energy for the underwater vehicles. Computational fluid dynamics simulations of the effect of geometric parameters, including the blade radius, chord length, and pitch angle, on the performance of the turbine are conducted. The Reynolds-Averaged Navier–Stokes equations are numerically solved with a sliding mesh method. Thirteen sets of tests in total are performed at different values of tip-speed ratios. The tests are divided into three groups to study the effect of the three parameters mentioned above, separately. The obtained power coefficients, coefficient of torque, and the dynamic torque on a blade are then compared in each group of tests. Pressure contours and velocity contours are given to explain the reason how the geometric parameters affect the rotor performance.

scholarly journals Investigation on Resistance, Squat and Ship-Generated Waves of Inland Convoy Passing Bridge Piers in a Confined Waterway

2021 ◽  
Vol 9 (10) ◽  
pp. 1125
Author(s):  
Peng Du ◽  
Abdellatif Ouahsine ◽  
Philippe Sergent ◽  
Yannick Hoarau ◽  
Haibao Hu
Keyword(s):  
Stokes Equations ◽  
Lateral Position ◽  
Wave Pattern ◽  
Body Motion ◽  
Bridge Piers ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Sliding Mesh ◽  
Experimental Approaches ◽  
Mesh Technique

The average and unsteady hydrodynamics of an inland convoy passing bridge piers in a confined waterway were investigated using both numerical and experimental approaches. The numerical simulations are realized by solving the RANS (Reynolds-averaged Navier–Stokes) equations accounting for the solid body motion using the sliding mesh technique, while the experiments were carried out in the towing tank. The advancing resistance, trim, sinkage and ship-generated waves were analyzed as functions of the water depth, distance between bridge piers, draught and velocity. The existence of the piers is found to only influence the transient hydrodynamics of the convoy, but not the averaged properties. The ship-generated waves, especially the wave profiles at a specific lateral position, were characterized. Two wave crests exist at the pier position because of the additional reflections, creating a very complex wave pattern in the confined waterway.

Numerical Modeling of Unsteady Flow Through a Turbomachine Stage

1998 ◽  
Author(s):  
R. I. Issa ◽  
M. A. Sadri
Keyword(s):  
Numerical Method ◽  
Periodic Boundary ◽  
Stokes Equations ◽  
Unsteady Flows ◽  
Periodic Boundary Conditions ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Sliding Mesh ◽  
Flow Through ◽  
Implicit Numerical Method

A numerical method is presented for the simulation of unsteady flows through turbomachine stages with unequal numbers of rotor and stator blades. The method solves the two-dimensional incompressible, unsteady, ensemble averaged, Navier-Stokes equations together with transport equations for the k–ϵ turbulence model employed to simulate the effects of turbulence. The method employs an implicit pressure-based finite volume discretisation procedure. In order to simulate the flow in the rotor and stator passages simultaneously, a sliding mesh methodology is developed which allows the mesh mapping the rotor domain to move in a sliding action relative to the static mesh which maps the stator passage. Phase-lagged periodic boundary conditions are implemented in the context of the implicit numerical method developed to handle unequal rotor and stator pitches efficiently. The effectiveness and accuracy of the method are assessed against data for a rotor/stator configuration with unequal pitches in adjacent rows of a low speed turbine.

A Continuum - Molecular Dynamics Hybrid Method for Micro- and Nano-Fluid Flow

2010 ◽  
Author(s):  
Ali Kharazmi ◽  
Reza Kamali
Keyword(s):  
Molecular Dynamics ◽  
Stokes Equations ◽  
Computer Code ◽  
Quantitative Agreement ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Nano Fluid ◽  
Dynamics Simulations ◽  
The Continuum ◽  
Overlap Region

A computer program based on a Molecular Dynamics-Continuum hybrid numerical method has been developed in which the Navier-Stokes equations are solved in the continuum region and the atomistic molecular dynamics in molecular region. The prepared algorithm and the computer code are capable of computing flows in micro and nano-scale geometries. The coupling between the continuum equations and the molecular dynamics is constructed through constrained dynamics within an overlap region where both molecular and continuum equations are solved simultaneously. An Overlap region is introduced in two directions to improve the choice of using molecular region in smaller areas. The proposed method is used to simulate steady and start-up Couette flow showing quantitative agreement with results from analytical solutions and full molecular dynamics simulations.

The Alteration of Runner and Partial Vanes on a Fixed Blade Propeller Water Turbine Basing on the Full Passage Simulation

2008 ◽  
Author(s):  
Lanjin Zhang ◽  
Zhengwei Wang ◽  
Qingqing He ◽  
Guangjie Peng
Keyword(s):  
Finite Element ◽  
Stokes Equations ◽  
Draft Tube ◽  
Internal Flow ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
High Loss ◽  
Water Turbine ◽  
Volume Method ◽  
Spiral Casing

Basing on the 3D-steady Navier-Stokes equations with standard k-ε turbulence closure models, non-structure mesh with fitted body coordinate and finite element based finite volume method, the internal flow on the full passage of the 6.5-meters head fixed blade propeller water turbine is analyzed. Numerical results show that the low output is caused by unsuitable full passage. The flow on the stay vanes isn’t uniform and the circumferential velocity of the runner rim is too large, which leads to a high loss in the draft tube. So the runner and partial stay vanes in the concrete spiral casing are redesigned. The output of the full passage with new runner and new partial stay vanes under 6.5-meters head is 295KW larger than the old one with 240KW output, and the efficiency is 81%, which is larger than former 70%. The redesign of runner and stay vanes is successful.

scholarly journals Multiphase Effects in Dynamic Systems Under Vibration

2016 ◽  
Author(s):  
Timothy J. O’Hern ◽  
John R. Torczynski ◽  
Jonathan R. Clausen
Keyword(s):  
Stokes Equations ◽  
Navier Stokes ◽  
Arbitrary Lagrangian Eulerian ◽  
Mesh Distortion ◽  
Navier Stokes Equations ◽  
Sliding Mesh ◽  
Vibrational Response ◽  
Near Resonance ◽  
Narrow Gaps ◽  
Piston Position

Analysis, simulations, and experiments are performed for a piston in a vibrated liquid-filled cylinder, where the damping caused by forcing liquid through narrow gaps depends almost linearly on the piston position. Adding a little gas completely changes the dynamics of this spring-mass-damper system when it is subject to vibration. When no gas is present, the piston’s vibrational response is highly overdamped due to the viscous liquid being forced through the narrow gaps. When a small amount of gas is added, Bjerknes forces cause some gas to migrate below the piston. The resulting pneumatic spring enables the liquid to move with the piston so that little liquid is forced through the gaps. This “Couette mode” thus has low damping and a strong resonance near the frequency given by the pneumatic spring constant and the piston mass. Near this frequency, the piston response is large, and the nonlinearity from the varying gap length produces a net force on the piston. This “rectified” force can be many times the piston’s weight and can cause the piston to compress its supporting spring. A surrogate system in which the gas regions are replaced by upper and lower bellows with similar compressibility is studied. A recently developed theory for the piston and bellows motions is compared to finite element simulations. The liquid obeys the unsteady incompressible Navier-Stokes equations, and the piston and the bellows obey Newton’s 2nd Law. Due to the large piston displacements near resonance, an Arbitrary Lagrangian Eulerian (ALE) technique with a sliding-mesh scheme is used to limit mesh distortion. Theory and simulation results for the piston motion are in good agreement. Experiments are performed with liquid only, with gas present, and with upper and lower bellows replacing the gas. Liquid viscosity, bellows compressibility, vibration amplitude, and gap geometry are varied to determine their effects on the frequency at which the rectified force makes the piston move down. This critical frequency is found to depend on whether the frequency is increased or decreased with time.

Effects of stator splitter blades on aerodynamic performance of a single-stage transonic axial compressor

2020 ◽  
Vol 14 (4) ◽  
pp. 7369-7378
Author(s):  
Ky-Quang Pham ◽  
Xuan-Truong Le ◽  
Cong-Truong Dinh
Keyword(s):  
Stokes Equations ◽  
Three Dimensional ◽  
Axial Compressor ◽  
Aerodynamic Performance ◽  
Numerical Results ◽  
Single Stage ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Operating Stability ◽  
Length Coverage

Splitter blades located between stator blades in a single-stage axial compressor were proposed and investigated in this work to find their effects on aerodynamic performance and operating stability. Aerodynamic performance of the compressor was evaluated using three-dimensional Reynolds-averaged Navier-Stokes equations using the k-e turbulence model with a scalable wall function. The numerical results for the typical performance parameters without stator splitter blades were validated in comparison with experimental data. The numerical results of a parametric study using four geometric parameters (chord length, coverage angle, height and position) of the stator splitter blades showed that the operational stability of the single-stage axial compressor enhances remarkably using the stator splitter blades. The splitters were effective in suppressing flow separation in the stator domain of the compressor at near-stall condition which affects considerably the aerodynamic performance of the compressor.

Sensitivity analysis for Navier-Stokes equations on unstructured meshes using complex variables

AIAA Journal ◽  
2001 ◽  
Vol 39 ◽  
pp. 56-63
Author(s):  
W. Kyle Anderson ◽  
James C. Newman ◽  
David L. Whitfield ◽  
Eric J. Nielsen
Keyword(s):  
Sensitivity Analysis ◽  
Stokes Equations ◽  
Unstructured Meshes ◽  
Complex Variables ◽  
Navier Stokes ◽  
Navier Stokes Equations
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