2020-11-26T16:53:40Z
http://scientiairanica.sharif.edu/?_action=export&rf=summon&issue=286
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2010
17
6
Eect of Different Configurations on 3-D Analysis of Flow Through Stay Vanes and Guide Vanes of a Francis Turbine
B.
Firoozabadi
R.
Dadfar
G.
Ahmadi
Stay and guide vanes (distributor) are essential parts of a turbine. They are used to control
the
ow rate and to appropriately transfer the
ow momentum to the runner. In this work,
ow through
the distributor is analyzed. For various Boundary Conditions (BC) and dierent congurations, threedimensional
ows in the distributor of a Francis turbine are evaluated and compared with each other. The
numerical simulations were carried out using Fluent software and the results were validated with a GAMM
Francis turbine, where the geometry and detailed best eciency measurements were publically available.
In these simulations, the
ow was assumed to be steady and the eect of turbulence was included using
the k ???? " turbulence model. The study showed that an accurate prediction of velocity and pressure elds
through the distributor may be obtained by considering a representative runner chamber with a single
passage, including one blade of a stay and guide vane conguration. Furthermore, the corresponding
needed computational resources for such an analysis are quite modest.
Francis turbine
Stay vane
Guide vane
3-D simulation
2010
12
01
http://scientiairanica.sharif.edu/article_3365_dd7c3e63ceeae9794f31466c0e4779a8.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2010
17
6
Two-Dimensional Numerical Investigation of a Micro Combustor
M.S.
Saidi
Abolfazl
Irani Rahaghi
M. B.
Shafii
M. H.
Saidi
In this paper, a two-dimensional numerical approach is used to study the eect of micro
combustor height, mass
ow rate and external convection heat transfer coecient on the temperature and
species mass fraction proles. A premixed mixture of H2-Air with a multi-step chemistry is used. The
transient gas phase energy and species conservation equations result in an Advection-Diusion-Reaction
system that leads to two sti systems of PDEs. In the present work, the computational domain is
solved through the Strang splitting method, which is suitable for a nonlinear sti system of PDEs. A
revised boundary condition for the velocity equation is applied and its eect on the
ow characteristics is
investigated. The results show that both convection heat transfer coecient and micro combustor height
have a signicant eect on the combustion and heat transfer rates in the micro scales. Also increasing
the convective heat transfer coecient and decreasing the height and inlet mixture velocity, decreases
temperature and active radicals along the micro combustor. In addition, the slip
ow and thermal creep
boundary conditions in the studied scales have no signicant eect on the dierent parameters, but changes
slightly the cross section proles of the temperature. The 2-D numerical results show that the micro
combustion must be treated as two dimensional.
Micro combustor
numerical
Combustion
Micro-scale
Two-dimensional
2010
12
01
http://scientiairanica.sharif.edu/article_3366_e36d28a4ba6421f093e90c2c300e1e0c.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2010
17
6
Rayan: A Polyhedral Grid Co-located Incompressible Finite Volume Solver (Part I: Basic Design Features)
M.S.
Saidi
M.
SANI
In this work, basic design features of Rayan are documented. One of the new design
features presented in this work is the way Rayan handles polyhedral grids. Grid denition is combined
with the denition of the structure of the sparse coecient matrix, thereby releasing a considerable
part of the memory used by the grid to store otherwise required faces belonging to the cell part of the
connectivity description. The key idea is to use a uniform way for creating the structure of the coecient
matrix from the grid connectivity description and to access that data when computing the elements of
the coecient matrix. This saving requires many modications to the computational algorithm details,
which are addressed. Computational method features include a SIMPLE-based pressure-velocity coupling
and co-located variable arrangement in which all
ow variables are stored at cell centers, and mass
uxes
are stored on face centers. Also handling convective and diusive
uxes is described. The throughput is
benchmark validated and shows second order truncation properties, both in time and space.
Arbitrary polyhedral
Unstructured
Unsteady
Incompressible
Co-located
2010
12
01
http://scientiairanica.sharif.edu/article_3367_f2c50c87a594dc727c58233e2cb59c47.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2010
17
6
Analysis of Manipulators Using SDRE: A Closed Loop Nonlinear Optimal Control Approach
M.
Irani
M. H.
Korayem
S.
Rafee Nekoo
In this paper, the State Dependent Riccati Equation (SDRE) method is implemented on
robotic systems such as a mobile two-links planar robot and a xed 6R manipulator with complicated
dynamic equations. Dynamic modelings of both cases are presented using the Lagrange method.
Afterwards, the Dynamic Load Carrying Capacity (DLCC), which is an important characteristic of robots,
is calculated for these two systems. DLCC is calculated for the predened end-eector path, where motor
torque limits and tracking error constraints are imposed for this calculation. For a mobile two-links planar
robot, the stability constraint is discussed by applying a zero moment point approach. A nonlinear feedback
control law is designed for the fully nonlinear dynamics of two cases using a nonlinear closed-loop optimal
control method. For solving the SDRE equation that appears in the optimal control solution, a power
series approximation method is applied. DLCC is obtained, subject to accuracy and torque constraints,
by applying this feedback control law for the square and linear path of the end-eector for mobile twolink
and a 6R manipulator, respectively. Finally, simulations are done for both cases and the DLCC of
manipulators is determined. Also, actual end-eector positions, required control eorts and the angular
position and velocity of joints are presented for full load conditions, and results are discussed
Mobile manipulator
6R robot
Nonlinear optimal control
DLCC
SDRE
2010
12
01
http://scientiairanica.sharif.edu/article_3368_debfc926cad7ab30e82d581a1e36b057.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2010
17
6
Experimental Investigation of Transition on a Plunging Airfoil
M. R.
Soltani
F.
Rasi Marzabadi
Extensive tests were carried out on a section of a wind turbine blade. The eect of reduced
frequency on the boundary layer transition point of the model oscillating in plunge has been investigated.
The spatial-temporal progressions of the transition point and the state of the unsteady boundary layer were
measured using multiple hot-lm sensors. The measurements showed that reduced frequency highly aects
variations of the transition point and results in a hysteresis loop in the dynamic transition locations. The
dominated frequencies of the boundary layer are found to be a function of the reduced frequency and mean
angle of attack.
Boundary layer transition
Plunging
Reduced frequency
Airfoil
Wind Turbine
2010
12
01
http://scientiairanica.sharif.edu/article_3369_af413a66059698a549aad7561abb8267.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2010
17
6
Experimental and Numerical Analysis of Turbulent Air Flow Around a Surface Mounted Hemisphere
M.
Yaghoubi
M.M.
Tavakol
The air
ow field around a surface mounted hemisphere for different velocities is
investigated experimentally and numerically. Hot-film anemometry is used in a wind tunnel to analyze
the
ow structure for different regions of
ow domain around the hemisphere. The
ow Reynolds number
is varied based on the hemisphere diameter and free stream velocities. The air velocity is taken as 5, 7
and 8.5 m/s, with corresponding Reynolds numbers of 35000, 50000 and 64000. To illustrate the
ow
pattern around the hemisphere, variations of
ow velocity at various vertical sections along the midplane,
and cross-stream velocities for various surfaces and heights, are measured and plotted. Corresponding
numerical solutions are also carried out to visualize the
ow reversal, horseshoe vortices and recirculation
zones around and downstream of the hemisphere. It is concluded that the
ow is highly Reynolds number
dependent, especially at the reversed
ow region upstream and downstream of the hemisphere. Moreover,
the eect of hemisphere location in the tunnel is studied, and velocity distributions are compared and
presented in the wake of the hemisphere for constant free stream velocity.
Hot-film anemometer
Reversed ow
Reynolds number
Wake structure
Turbulent ow
2010
12
01
http://scientiairanica.sharif.edu/article_3370_c6ef644791be52b01639315d5a565ac3.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2010
17
6
Experimental Study of Small and Medium Break LOCA in the TTL-2 Thermo-Hydraulic Test Loop and Its Modeling with RELAP5/MOD3.2 Code
M.
Taherzadeh
J.
Jafari
H.
Arabnezhad
N.
Vosoughi
Small and medium break LOCA accidents at low pressure and under low velocity conditions
have been studied in the TTL-2 Thermo-hydraulic Test Loop, experimentally. TTL-2 is a thermal
hydraulic test facility which is designed and constructed in NSTRI to study thermal hydraulic parameters
under normal operational and accident conditions of nuclear research reactors. A nodalization has been
developed for the TTL-2 and experimental results have been compared with RELAP5/MOD3.2 results.
The considered accidents are a 25% and 50% cold leg break without emergency core cooling systems.
Results show good agreement between experiments and RELAP5/MOD3.2 results. This research provides
experimental data for evaluation of thermo hydraulic codes for nuclear research reactors, and veries
that RELAP5/MOD3.2 has a good capability to estimate the thermal hydraulic behavior of low pressure
and low velocity thermal hydraulic systems, such as research reactors under steady state and transient
conditions.
TTL-2 thermal hydraulic test loop
LOCA
RELAP5/MOD3.2
Experimental results
Code validation
Research reactor
2010
12
01
http://scientiairanica.sharif.edu/article_3371_754a8719a61cf3d431919c324e106a18.pdf