Impact on the Performance of Micro-Nozzle Straight Exit Section

2014 ◽  
Vol 635-637 ◽  
pp. 26-30
Author(s):  
Jun Jie Tong ◽  
Yun Hui Fang
Keyword(s):  
Stokes Equations ◽  
Maximum Velocity ◽  
Flow Coefficient ◽  
Navier Stokes ◽  
Exit Section ◽  
Thrust Coefficient ◽  
Navier Stokes Equations ◽  
Micro Nozzle ◽  
Pressure Contour ◽  
Velocity Contour

The FLUENT6.3 software is applied to simulate the supersonic flow in micro convergent-divergent nozzle. The simulation is complemented by computing steady 2-D Navier-stokes equations to analyze the pressure contour and velocity contour inside the micro nozzle which has straight exit section or not and the length of straight exit section l. Also the performances of fluent mass coefficients and thrust force efficiencies are studied. The numerical results show: That the nozzle has straight exit section or not and the section length l affect the pressure contour and velocity contour inside the thruster. Compared to the nozzle that has no straight exit section, the minimum pressure region and the maximum velocity region are close to the center of exit in the nozzle that has straight exit section. Also the affected region is increased. When the throat Reynolds number Re is small, the flow coefficient Cd and thrust coefficient ηF firstly increase then decrease with the increase of l.

scholarly journals Three Dimensional Effect of Axial Magnetic Field to Suppress Convection in the Solvent of Ge0.98Si0.02 Grown By the Traveling Solvent Method

2021 ◽  
Author(s):  
Leily Abidi
Keyword(s):  
Magnetic Field ◽  
Stokes Equations ◽  
Axial Magnetic Field ◽  
Three Dimensional ◽  
Maximum Velocity ◽  
Navier Stokes ◽  
Growth Interface ◽  
Navier Stokes Equations ◽  
Solvent Method ◽  
Element Technique

A three dimensional numerical simulation of the effect of an axial magnetic field on the fluid flow, heat and mass transfer within the solvent of GE0.98Si0.02 grown by the travelling solvent method is presented. The full steady state Navier-Stokes equations, as well as the energy, continuity and the mass transport equations, were solved numerically using the finite element technique. It is found that a strong convective flow exists in the solvent, which is known to be undesirable to achieve a uniform crystal. An external axial magnetic field is applied to suppress this convection. By increasing the magnetic induction, it is observed that the intensity of the flow at the centre of the crucible reduces at a faster rate than near the wall. This phenomenon creates a stable and flat growth interface and the silicon distribution in the horizontal plane becomes relatively homocentric. The maximum velocity is found to obey a power law with respect to the Hartmann number Umax Ha⁻⁷/⁴

scholarly journals Three Dimensional Effect of Axial Magnetic Field to Suppress Convection in the Solvent of Ge0.98Si0.02 Grown By the Traveling Solvent Method

2021 ◽  
Author(s):  
Leily Abidi
Keyword(s):  
Magnetic Field ◽  
Stokes Equations ◽  
Axial Magnetic Field ◽  
Three Dimensional ◽  
Maximum Velocity ◽  
Navier Stokes ◽  
Growth Interface ◽  
Navier Stokes Equations ◽  
Solvent Method ◽  
Element Technique

A three dimensional numerical simulation of the effect of an axial magnetic field on the fluid flow, heat and mass transfer within the solvent of GE0.98Si0.02 grown by the travelling solvent method is presented. The full steady state Navier-Stokes equations, as well as the energy, continuity and the mass transport equations, were solved numerically using the finite element technique. It is found that a strong convective flow exists in the solvent, which is known to be undesirable to achieve a uniform crystal. An external axial magnetic field is applied to suppress this convection. By increasing the magnetic induction, it is observed that the intensity of the flow at the centre of the crucible reduces at a faster rate than near the wall. This phenomenon creates a stable and flat growth interface and the silicon distribution in the horizontal plane becomes relatively homocentric. The maximum velocity is found to obey a power law with respect to the Hartmann number Umax Ha⁻⁷/⁴

Simulation of Microfluidic Flow Using Ferrofluids

2008 ◽  
Author(s):  
Akshay C. Gunde ◽  
Sushanta K. Mitra
Keyword(s):  
Magnetic Field ◽  
External Magnetic Field ◽  
Flow Control ◽  
Magnetic Particles ◽  
Stokes Equations ◽  
Maximum Velocity ◽  
Additional Term ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Microfluidic Flow

Present day microfluidics widely uses electrokinetic effects like eletrosmosis and electrophoresis to achieve flow control. These methods require extensive micromachining processes. Also, the fabrication of valves and valve-seats is difficult, which frequently leads to leakages and eventual breakdown of the system. This paper introduces the use of ferrofluids as an alternative for flow control in microchannels. Numerical simulation of flow through a microchannel using a ferrofluid in the presence of an external magnetic field is performed by coupling the flow and magnetic phenomena. An additional term calculated from the ferrofluid magnetization equations, is introduced in the Navier-Stokes equations to account for the magnetic force. The maximum velocity in a magnetically driven flow is shown to be a linear function of magnitude of magnetization of the permanent magnet. Further, the insertion of micron-size magnetic particles (referred here as magnetic plugs) in the flow field has been discussed. These plugs can be used to provide appropriate barriers to the flow by controlling their movement externally. Using the combination of ferrofluid and magnetic plugs, flow control can be achieved by the variation of external magnetic field alone.

Numerical analysis on effects of blade number on hydrodynamic performance of low-pitch marine cycloidal propeller

2019 ◽  
Vol 234 (2) ◽  
pp. 490-501
Author(s):  
Mohammad Bakhtiari ◽  
Hassan Ghassemi
Keyword(s):  
Numerical Method ◽  
Stokes Equations ◽  
Thrust Force ◽  
Circular Disk ◽  
Hydrodynamic Performance ◽  
Navier Stokes ◽  
Thrust Coefficient ◽  
Navier Stokes Equations ◽  
Blade Number ◽  
Marine Propulsion

Marine cycloidal propeller, as a special type of marine propulsion system, is used for ships that require high maneuverability, such as tugs and ferries. In a marine cycloidal propeller, the thrust force is generated by rotation of a circular disk with a number of lifting blades fitted on the periphery of the disk, so that the propeller axis of rotation is perpendicular to the direction of thrust force. Each blade pitches about its own axis, and the thrust magnitude and direction can be adjusted by controlling the pitching angle of the blades. Therefore, the propulsion and maneuvering units are combined together and no separate rudder is needed to maneuver the ship. Two configurations of marine cycloidal propeller have been studied and developed based on propeller pitch: low-pitch propeller (designed for advance coefficient less than one, means λ < 1) and high-pitch propeller (designed for λ > 1). Low-pitch marine cycloidal propellers are used in applications with low-speed maneuvering requirements, such as tugboats and minesweepers. In this study, the effects of blade number on hydrodynamic performance of low-pitch marine cycloidal propeller with pure cycloidal motion of the blades are investigated. The turbulent flow around marine cycloidal propeller is solved using a 2.5D numerical method based on unsteady Reynolds-averaged Navier–Stokes equations with shear-stress transport k–ω turbulent model. The presented numerical method was validated against experimental data and showed good agreement. The results showed that the thrust coefficient of marine cycloidal propeller generally decreases by increasing the blade number, whereas the torque coefficient increases. Consequently, the hydrodynamic efficiency of marine cycloidal propeller drops as the blade number increases.

scholarly journals CFD Analysis of the First-Stage Rotor and Stator in a Two-Stage Mixed Flow Pump

2005 ◽  
Vol 2005 (1) ◽  
pp. 23-29 ◽  
Author(s):  
Steven M. Miner
Keyword(s):  
Stokes Equations ◽  
Flow Coefficient ◽  
Navier Stokes ◽  
Design Parameters ◽  
Mixed Flow ◽  
Two Stage ◽  
Navier Stokes Equations ◽  
Pressure Profiles ◽  
Turbulence Effects ◽  
Flow Pump

A commercial computational fluid dynamics (CFD) code is used to compute the flow field within the first-stage rotor and stator of a two-stage mixed flow pump. The code solves the 3D Reynolds-averaged Navier-Stokes equations in rotating and stationary cylindrical coordinate systems for the rotor and stator, respectively. Turbulence effects are modeled using a standardk−εturbulence model. Stage design parameters are rotational speed890 rpm, flow coefficientφ=0.116, head coefficientψ=0.094, and specific speed2.01(5475 US). Results from the study include velocities, and static and total pressures for both the rotor and stator. Comparison is made to measured data for the rotor. The comparisons in the paper are for circumferentially averaged results and include axial and tangential velocities, static pressure, and total pressure profiles. Results of this study show that the computational results closely match the shapes and magnitudes of the measured profiles, indicating that CFD can be used to accurately predict performance.

scholarly journals ЧИСЛЕННОЕ МОДЕЛИРОВАНИЕ ВЗАИМОДЕЙСТВИЯ НЕДОРАСШИРЕННОЙ СВЕРХЗВУКОВОЙ СТРУИ ГАЗА С ПЛОСКОЙ ПРЕГРАДОЙ

2018 ◽  
Vol 26 (4) ◽  
pp. 73-80
Author(s):  
С.А. Николин ◽  
А.А. Приходько
Keyword(s):  
Experimental Data ◽  
Stokes Equations ◽  
Gas Jet ◽  
Navier Stokes ◽  
Exit Section ◽  
Nozzle Exit Section ◽  
Navier Stokes Equations ◽  
Supersonic Gas Jet ◽  
Calculated Region ◽  
Flat Obstacle

The results of numerical modeling based on the nonstationary Reynolds-averaged Navier – Stokes equations for the interaction of an underexpanded supersonic gas jet with a flat obstacle, which was established at different distances from the nozzle exit section are presented. The results of the calculations are presented in the form of the distribution of the Mach number and the density gradient in the calculated region, and the pressure and friction coefficients over the surface of the plate. The results of the numerical calculation are compared with the experimental data.

scholarly journals FEATURES OF MODELING THE FLOW AROUND THE HELICOPTER MAIN ROTOR TAKING INTO ACCOUNT ARBITRARY BLADES MOTION

2019 ◽  
Vol 22 (3) ◽  
pp. 25-34
Author(s):  
V. A. Vershkov ◽  
B. S. Kritsky ◽  
R. M. Mirgazov
Keyword(s):  
Turbulence Model ◽  
Stokes Equations ◽  
Navier Stokes ◽  
Incoming Flow ◽  
Main Rotor ◽  
Thrust Coefficient ◽  
Navier Stokes Equations ◽  
Ansys Cfx ◽  
Sst Turbulence Model ◽  
Helicopter Main Rotor

The article considers the problem of the flow around the helicopter main rotor taking into account blades flapping in the plane of rotation and in the plane of thrust as well as the elastic blades deformation. The rotor rotation is modeled by the method of converting Navier-Stokes equations from a fixed coordinate system associated with the incoming flow into a rotating system associated with the rotor hub. For axial flow problems, this makes it possible to formulate the problem as stationary at a constant rotational speed of rotor. For a mode of skewed flow around the rotor in the terms of incident flow in this system it is necessary to solve the non-stationary problem. To solve the problem, the method of deformable grids is used, in which the equations are copied taking into account the grid nodes motion determined in accordance with the spatial blades motion, and SST turbulence model is used for closure. The results of the test calculations of the main rotor aerodynamic characteristics with and without blade flapping are presented in this paper. The coefficients of the main rotor thrust cT and the blades hinge moments mh are compared. The calculations were carried out in the CFD software ANSYS CFX (TsAGI License No. 501024). The flow around a four-bladed main rotor of a radius of 2.5 meters is modeled in the regime of skewed flow. The speed of the incoming flow came to 85 m/s under normal atmospheric conditions. The rotor was at an angle of attack of −10˚. To calculate the rotor motion without taking into account the flapping movements, we used the nonstationary system of Navier-Stokes equations with the closure with SST turbulence model. The calculation was being carried out until the change in the maximum value of the rotor thrust during one revolution became less than 1%. For modeling flapping blade movements, the control laws and equations describing the angle of blade flapping as a function from its azimuth angle obtained from the experiment were used. The procedure for reconstructing the grid according to a given law was conducted using standard grid deformation methods presented in the ANSYS CFX software. When solving the nonstationary Navier-Stokes equations, a dual time step was used. The obtained results show that accounting of the effect of flapping movements and cyclic control of the blades has an impact on the character of changing the main rotor thrust coefficient during one revolution and significantly changes the shape of the graph of the hinge moment coefficient of each blade.

Laminar flow in a square duct of strong curvature

1977 ◽  
Vol 83 (3) ◽  
pp. 509-527 ◽  
Author(s):  
J. A. C. Humphrey ◽  
A. M. K. Taylor ◽  
J. H. Whitelaw
Keyword(s):  
Stokes Equations ◽  
Laser Doppler Anemometry ◽  
Longitudinal Velocity ◽  
Flow Analysis ◽  
Maximum Velocity ◽  
Outer Wall ◽  
Navier Stokes ◽  
Upstream Region ◽  
Dean Number ◽  
Navier Stokes Equations

Calculated values of the three velocity components and measured values of the longitudinal component are reported for the flow of water in a 90° bend of 40 x 40mm cross-section; the bend had a mean radius of 92mm and was located downstream of a 1[sdot ]8m and upstream of a 1[sdot ]2m straight section. The experiments were carried out at a Reynolds number, based on the hydraulic diameter and bulk velocity, of 790 (corresponding to a Dean number of 368). Flow visualization was used to identify qualitatively the characteristics of the flow and laser-Doppler anemometry to quantify the velocity field. The results confirm and quantify that the location of maximum velocity moves from the centre of the duct towards the outer wall and, in the 90° plane, is located around 85% of the duct width from the inner wall. Secondary velocities up to 65% of the bulk longitudinal velocity were calculated and small regions of recirculation, close to the outer corners of the duct and in the upstream region, were also observed.The calculated results were obtained by solving the Navier–Stokes equations in cylindrical co-ordinates. They are shown to exhibit the same trends as the experiments and to be in reasonable quantitative agreement even though the number of node points used to discretize the flow for the finite-difference solution of the differential equations was limited by available computer time and storage. The region of recirculation observed experimentally is confirmed by the calculations. The magnitude of the various terms in the equations is examined to determine the extent to which the details of the flow can be represented by reduced forms of the Navier–Stokes equations. The implications of the use of so-called ‘partially parabolic’ equations and of potential- and rotational-flow analysis of an ideal fluid are quantified.

Study of Three-Dimensional Wall Effects on Micro Nozzle’s Performance

2011 ◽  
Vol 308-310 ◽  
pp. 1497-1504
Author(s):  
Jun Jie Tong ◽  
Ji Wen Cen ◽  
Jin Liang Xu
Keyword(s):  
Stokes Equations ◽  
Three Dimensional ◽  
Numerical Results ◽  
Navier Stokes ◽  
Two Dimensional ◽  
Test Results ◽  
Wall Effects ◽  
Navier Stokes Equations ◽  
Micro Nozzle ◽  
Test Process

According to the lever moment equilibrium, the thrust test is performed for a flat micro convergent-divergent micro nozzle with 11.72 geometry expansion ratios. During the test process, since the distances between the Piezoelectric sensors point and the bearing point are much larger than the distance between the nozzle and the bearing point, thus the thrust signal is amplified. Compared with the test results, the FLUENT6.1 software is also applied to compute steady two-dimensional and three-dimensional Navier-stokes equations for numerical results by parallel computing. The numerical results and test results show that： for the flat micro nozzle with small ratio of throat depth and width, three-dimensional wall effects are not negligible. Three-dimensional numerical results agree well with the test results while there are large differences between two-dimensional numerical results and test results. With the throat Renaults being increased, the corresponding differences between two-dimensional numerical results and test results decreased accordingly

scholarly journals Wake structure of a transversely rotating sphere at moderate Reynolds numbers

2009 ◽  
Vol 621 ◽  
pp. 103-130 ◽  
Author(s):  
M. GIACOBELLO ◽  
A. OOI ◽  
S. BALACHANDAR
Keyword(s):  
Vortex Shedding ◽  
Free Stream ◽  
Stokes Equations ◽  
Maximum Velocity ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Stream Velocity ◽  
Wake Structure ◽  
Navier Stokes Equations ◽  
Chebyshev Spectral Collocation

The uniform flow past a sphere undergoing steady rotation about an axis transverse to the free stream flow was investigated numerically. The objective was to reveal the effect of sphere rotation on the characteristics of the vortical wake structure and on the forces exerted on the sphere. This was achieved by solving the time-dependent, incompressible Navier–Stokes equations, using an accurate Fourier–Chebyshev spectral collocation method. Reynolds numbers Re of 100, 250 and 300 were considered, which for a stationary sphere cover the axisymmetric steady, non-axisymmetric steady and vortex shedding regimes. The study identified wake transitions that occur over the range of non-dimensional rotational speeds Ω* = 0 to 1.00, where Ω* is the maximum velocity on the sphere surface normalized by the free stream velocity. At Re = 100, sphere rotation triggers a transition to a steady double-threaded structure. At Re = 250, the wake undergoes a transition to vortex shedding for Ω* ≥ 0.08. With an increasing rotation rate, the recirculating region is progressively reduced until a further transition to a steady double-threaded wake structure for Ω* ≥ 0.30. At Re = 300, wake shedding is suppressed for Ω* ≥ 0.50 via the same mechanism found at Re = 250. For Ω* ≥ 0.80, the wake undergoes a further transition to vortex shedding, through what appears to be a shear layer instability of the Kelvin–Helmholtz type.

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