**Commenced**in January 2007

**Frequency:**Monthly

**Edition:**International

**Paper Count:**2293

# Search results for: Unsteady flow

##### 2293 Investigation on Unsteady Flow of a Turbine Stage with Negative Bowed Stator

**Authors:**
Keke Gao,
Tao Lin,
Yonghui Xie,
Di Zhang

**Abstract:**

Complicated unsteady flow in axial turbines produces high-frequency unsteady aerodynamic exciting force, which threatens the safe operation of turbines. This paper illustrates how negative-bowed stator reduces the rotor unsteady aerodynamic exciting force by unsteady flow field. With the support of three-dimensional viscous compressible Navier-Stokes equation, the single axial turbines with 0, -10 and -20 degree bowed stator are comparably investigated, aiming to identify the flow field structure difference caused by various negative-bowed degrees. The results show that negative-bowed stator strengthens the turbulence kinetic energy, which is further strengthened with the increase of negative-bowed degree. Meanwhile, the flow phenomenon including stator wakes and passage vortex is shown. In addition, the interaction of upstream negative-bowed wakes contributes to the reduction of unsteady blade load fluctuation. Furthermore, the aerodynamic exciting force decreases with the increasing negative bowed degree, while the efficiency is correspondingly reduced. This paper provides the reference for the alleviation of the harmful impact caused by unsteady interaction with the method of wake control.

**Keywords:**
Unsteady flow,
axial turbine,
wake,
aerodynamic force,
loss.

##### 2292 Unsteady Flow and Heat Transfer of Nanofluid from Circular Tube in Cross-Flow

**Authors:**
H. Bayat,
M. Majidi,
M. Bolhasani,
A. Karbalaie Alilou,
A. Mirabdolah Lavasani

**Abstract:**

Unsteady flow and heat transfer from a circular cylinder in cross-flow is studied numerically. The governing equations are solved by using finite volume method. Reynolds number varies in range of 50 to 200; in this range flow is considered to be laminar and unsteady. Al2O3 nanoparticle with volume fraction in range of 5% to 20% is added to pure water. Effects of adding nanoparticle to pure water on lift and drag coefficient and Nusselt number is presented. Addition of Al2O3 has inconsiderable effect on the value of drags and lift coefficient. However, it has significant effect on heat transfer; results show that heat transfer of Al2O3 nanofluid is about 9% to 36% higher than pure water.

**Keywords:**
Nanofluid,
heat transfer,
unsteady flow,
forced
convection,
cross-flow.

##### 2291 Unsteadiness Effects on Variable Thrust Nozzle Performance

**Authors:**
A. M. Tahsini,
S. T. Mousavi

**Abstract:**

The purpose of this paper is to elucidate the flow unsteady behavior for moving plug in convergent-divergent variable thrust nozzle. Compressible axisymmetric Navier-Stokes equations are used to study this physical phenomenon. Different velocities are set for plug to investigate the effect of plug movement on flow unsteadiness. Variation of mass flow rate and thrust are compared under two conditions: First, the plug is placed at different positions and flow is simulated to reach the steady state (quasi steady simulation) and second, the plug is moved with assigned velocity and flow simulation is coupled with plug movement (unsteady simulation). If plug speed is high enough and its movement time scale is at the same order of the flow time scale, variation of the mass flow rate and thrust level versus plug position demonstrate a vital discrepancy under the quasi steady and unsteady conditions. This phenomenon should be considered especially from response time viewpoints in thrusters design.

**Keywords:**
Nozzle,
Numerical study,
Unsteady,
Variable thrust.

##### 2290 Unsteady Boundary Layer Flow over a Stretching Sheet in a Micropolar Fluid

**Authors:**
Roslinda Nazar,
Anuar Ishak,
Ioan Pop

**Abstract:**

**Keywords:**
Boundary layer,
micropolar fluid,
stretching surface,
unsteady flow.

##### 2289 Unsteady Flow between Two Concentric Rotating Spheres along with Uniform Transpiration

**Authors:**
O. Mahian,
A. B. Rahimi,
A. Kianifar,
A. Jabari Moghadam

**Abstract:**

**Keywords:**
Concentric spheres,
numerical study,
suction andblowing,
unsteady flow,
viscous torque.

##### 2288 Unsteady Free Convection Flow Over a Three-Dimensional Stagnation Point With Internal Heat Generation or Absorption

**Authors:**
Mohd Ariff Admon,
Abdul Rahman Mohd Kasim,
Sharidan Shafie

**Abstract:**

**Keywords:**
Free convection,
Boundary layer flow,
Stagnationpoint,
Heat generation

##### 2287 Heat Transfer Characteristics on Blade Tip with Unsteady Wake

**Authors:**
Minho Bang,
Seok Min Choi,
Jun Su Park,
Hokyu Moon,
Hyung Hee Cho

**Abstract:**

Present study investigates the effect of unsteady wakes on heat transfer in blade tip. Heat/mass transfer was measured in blade tip region depending on a variety of strouhal number by naphthalene sublimation technique. Naphthalene sublimation technique measures heat transfer using a heat/mass transfer analogy. Experiments are performed in linear cascade which is composed of five turbine blades and rotating rods. Strouhal number of inlet flow are changed ranging from 0 to 0.22. Reynolds number is 100,000 based on 11.4 m/s of outlet flow and axial chord length. Three different squealer tip geometries such as base squealer tip, vertical rib squealer tip, and camber line squealer tip are used to study how unsteady wakes affect heat transfer on a blade tip. Depending on squealer tip geometry, different flow patterns occur on a blade tip. Also, unsteady wakes cause reduced tip leakage flow and turbulent flow. As a result, as strouhal number increases, heat/mass transfer coefficients decrease due to the reduced leakage flow. As strouhal number increases, heat/ mass transfer coefficients on a blade tip increase in vertical rib squealer tip.

**Keywords:**
Gas turbine,
blade tip,
heat transfer,
unsteady wakes.

##### 2286 Numerical Flow Simulation around HSP Propeller in Open Water and behind a Vessel Wake Using RANS CFD Code

**Authors:**
Kadda Boumediene,
Mohamed Bouzit

**Abstract:**

The prediction of the flow around marine propellers and vessel hulls propeller interaction is one of the challenges of Computational fluid dynamics (CFD). The CFD has emerged as a potential tool in recent years and has promising applications. The objective of the current study is to predict the hydrodynamic performances of HSP marine propeller in open water and behind a vessel. The unsteady 3-D flow was modeled numerically along with respectively the K-ω standard and K-ω SST turbulence models for steady and unsteady cases. The hydrodynamic performances such us a torque and thrust coefficients and efficiency show good agreement with the experiment results.

**Keywords:**
Seiun Maru propeller,
steady,
unsteady,
CFD,
HSP.

##### 2285 Unsteady Stagnation-Point Flow towards a Shrinking Sheet with Radiation Effect

**Authors:**
F. M. Ali,
R. Nazar,
N. M. Arifin,
I. Pop

**Abstract:**

In this paper, the problem of unsteady stagnation-point flow and heat transfer induced by a shrinking sheet in the presence of radiation effect is studied. The transformed boundary layer equations are solved numerically by the shooting method. The influence of radiation, unsteadiness and shrinking parameters, and the Prandtl number on the reduced skin friction coefficient and the heat transfer coefficient, as well as the velocity and temperature profiles are presented and discussed in detail. It is found that dual solutions exist and the temperature distribution becomes less significant with radiation parameter.

**Keywords:**
Heat transfer,
Radiation effect,
Shrinking sheet Unsteady flow.

##### 2284 Unsteady Laminar Boundary Layer Forced Flow in the Region of the Stagnation Point on a Stretching Flat Sheet

**Authors:**
A. T. Eswara

**Abstract:**

**Keywords:**
Forced flow,
Keller-box method,
Stagnation point,
Stretching flat sheet,
Unsteady laminar boundary layer,
Velocity ratio parameter.

##### 2283 Unsteady Aerodynamics of Multiple Airfoils in Configuration

**Authors:**
Hossain Aziz,
Rinku Mukherjee

**Abstract:**

**Keywords:**
Aerodynamics,
Airfoils,
Configuration,
Unsteady.

##### 2282 Unsteady Water Boundary Layer Flow with Non-Uniform Mass Transfer

**Authors:**
G. Revathi,
P. Saikrishnan

**Abstract:**

**Keywords:**
Boundary layer,
heat transfer,
non-similar solution,
non-uniform mass,
unsteady flow.

##### 2281 Description of Unsteady Flows in the Cuboid Container

**Authors:**
K. Horáková,
K. Fraňa,
V. Honzejk

**Abstract:**

This part of study deals with description of unsteady isothermal melt flow in the container with cuboid shape. This melt flow is driven by rotating magnetic field. Input data (instantaneous velocities, grid coordinates and Lorentz forces) were obtained from in-house CFD code (called NS-FEM3D) which uses DDES method of computing. Description of the flow was performed by contours of Lorentz forces and caused velocity field. Taylor magnetic numbers of the flow were used 1.10^6, 5.10^6 and 1.10^7, flow was in 3D turbulent flow regime.

**Keywords:**
In-house computing code,
Lorentz forces,
magnetohydrodynamics,
rotating magnetic field.

##### 2280 Unsteady 3D Post-Stall Aerodynamics Accounting for Effective Loss in Camber Due to Flow Separation

**Authors:**
Aritras Roy,
Rinku Mukherjee

**Abstract:**

**Keywords:**
Post-stall,
unsteady,
wing,
aerodynamics.

##### 2279 Unsteady Heat and Mass Transfer in MHD Flow of Nanofluids over Stretching Sheet with a Non-Uniform Heat Source/Sink

**Authors:**
Bandaris Shankar,
Yohannes Yirga

**Abstract:**

In this paper, the problem of heat and mass transfer in unsteady MHD boundary-layer flow of nanofluids over stretching sheet with a non uniform heat source/sink is considered. The unsteadiness in the flow and temperature is caused by the time-dependent stretching velocity and surface temperature. The unsteady boundary layer equations are transformed to a system of non-linear ordinary differential equations and solved numerically using Keller box method. The velocity, temperature, and concentration profiles were obtained and utilized to compute the skin-friction coefficient, local Nusselt number, and local Sherwood number for different values of the governing parameters viz. solid volume fraction parameter, unsteadiness parameter, magnetic field parameter, Schmidt number, space-dependent and temperature-dependent parameters for heat source/sink. A comparison of the numerical results of the present study with previously published data revealed an excellent agreement.

**Keywords:**
Manetohydrodynamics,
nanofluid,
non-uniform heat source/sink,
unsteady.

##### 2278 Study of the Flow Structure in a Penstock in Unsteady Regime

**Authors:**
F. Nkontchou Ngongang,
M. Tchawe Tchawe,
B. Djeumako,
B. Kenmeugne

**Abstract:**

In this work, the flow structure in the Songloulou dam, is visualized in a time interval to observe the different fluid layers in our structure. Firstly, the three-dimensional modelling of the penstock is carried out in the software Gambit, followed by calculations in Fluent that proceeds introduction of boundary conditions. After calculation, we identified four periods corresponding to four regimes. In the first, spanning from 0.00 to 1.50s, we have the non-developed hydraulically rough turbulent regime, characterized by abrupt variations with modifications of the velocity fields. The second extends from 1.50 to 3.50s, where we have the transition regime characterized by slight variations and modifications of the velocity fields but with a great difference of the values of the current lines. From 3.50 to 5.00s, we encounter the third, which is the fully developed turbulent hydraulically rough regime, characterized by fields that vary no more, but have minute differences in the streamlines. The last period is from 5.00s and more, where we have a flow that is almost stationary, hence there are no changes in the fields.

**Keywords:**
Unsteady flow,
penstock,
friction coefficient,
hydroelectric dam.

##### 2277 CFD of Oscillating Airfoil Pitch Cycle by using PISO Algorithm

**Authors:**
Muhammad Amjad Sohail,
Rizwan Ullah

**Abstract:**

**Keywords:**
Angle of attack,
Centre of pressure,
subsonic flow,
pitching moment coefficient,
turbulence mode

##### 2276 A Fast, Portable Computational Framework for Aerodynamic Simulations

**Authors:**
Mehdi Ghommem,
Daniel Garcia,
Nathan Collier,
Victor Calo

**Abstract:**

**Keywords:**
Unsteady aerodynamics,
numerical simulations,
mixed-language approach,
potential flow.

##### 2275 Shear Layer Investigation through a High-Load Cascade in Low-Pressure Gas Turbine Conditions

**Authors:**
Mehdi Habibnia Rami,
Shidvash Vakilipour,
Mohammad H. Sabour,
Rouzbeh Riazi,
Hossein Hassannia

**Abstract:**

This paper deals with the steady and unsteady flow behavior on the separation bubble occurring on the rear portion of the suction side of T106A blade. The first phase was to implement the steady condition capturing the separation bubble. To accurately predict the separated region, the effects of three different turbulence models and computational grids were separately investigated. The results of Large Eddy Simulation (LES) model on the finest grid structure are acceptably in a good agreement with its relevant experimental results. The second phase is mainly to address the effects of wake entrance on bubble disappearance in unsteady situation. In the current simulations, from what was suggested in an experiment, simulating the flow unsteadiness, with concentrations on small scale disturbances instead of simulating a complete oncoming wake, is the key issue. Subsequently, the results from the current strategy to apply the effects of the wake and two other experimental work were compared to be in a good agreement. Between the two experiments, one of them deals with wake passing unsteady flow, and the other one implements experimentally the same approach as the current Computational Fluid Dynamics (CFD) simulation.

**Keywords:**
T106A turbine cascade,
shear-layer separation,
steady and unsteady conditions,
turbulence models,
OpenFOAM.

##### 2274 Analytical solution of Gas Flow Through a Micro-Nano Porous Media by Homotopy Perturbation method

**Authors:**
Jamal Amani Rad,
Kourosh Parand

**Abstract:**

**Keywords:**
Unsteady gas equation,
Homotopy perturbation method(HPM),
Porous medium,
Nonlinear ODE

##### 2273 Conjugate Heat transfer over an Unsteady Stretching Sheet Mixed Convection with Magnetic Effect

**Authors:**
Kai-Long Hsiao

**Abstract:**

**Keywords:**
Finite-difference method,
Conjugate heat transfer,
Unsteady Stretching Sheet,
MHD,
Mixed convection.

##### 2272 Numerical Evaluation of the Aerodynamic Efficiency of the Stevens and Jolly Vertical- Axis Windmill (1895)

**Authors:**
M. Raciti Castelli,
E. Benini

**Abstract:**

**Keywords:**
CFD,
vertical-axis rotor,
windmill.

##### 2271 Bifurcations and Chaotic Solutions of Two-dimensional Zonal Jet Flow on a Rotating Sphere

**Authors:**
Eiichi Sasaki,
Shin-ichi Takehiro,
Michio Yamada

**Abstract:**

**Keywords:**
rotating sphere,
two-dimensional flow,
bifurcationstructure

##### 2270 Radiation Effects on the Unsteady MHD Free Convection Flow Past in an Infinite Vertical Plate with Heat Source

**Authors:**
Tusharkanta Das,
Tumbanath Samantara,
Sukanta Kumar Sahoo

**Abstract:**

Unsteady effects of MHD free convection flow past in an infinite vertical plate with heat source in presence of radiation with reference to all critical parameters that appear in field equations are studied in this paper. The governing equations are developed by usual Boussinesq’s approximation. The problem is solved by using perturbation technique. The results are obtained for velocity, temperature, Nusselt number and skin-friction. The effects of magnetic parameter, prandtl number, Grashof number, permeability parameter, heat source/sink parameter and radiation parameter are discussed on flow characteristics and shown by means of graphs and tables.

**Keywords:**
Heat transfer,
radiation,
MHD,
free convection,
porous medium,
suction.

##### 2269 Unsteady Poiseuille Flow of an Incompressible Elastico-Viscous Fluid in a Tube of Spherical Cross Section on a Porous Boundary

**Authors:**
Sanjay Baburao Kulkarni

**Abstract:**

Exact solution of an unsteady flow of elastico-viscous fluid through a porous media in a tube of spherical cross section under the influence of constant pressure gradient has been obtained in this paper. Initially, the flow is generated by a constant pressure gradient. After attaining the steady state, the pressure gradient is suddenly withdrawn and the resulting fluid motion in a tube of spherical cross section by taking into account of the porosity factor of the bounding surface is investigated. The problem is solved in twostages the first stage is a steady motion in tube under the influence of a constant pressure gradient, the second stage concern with an unsteady motion. The problem is solved employing separation of variables technique. The results are expressed in terms of a nondimensional porosity parameter (K) and elastico-viscosity parameter (β), which depends on the Non-Newtonian coefficient. The flow parameters are found to be identical with that of Newtonian case as elastic-viscosity parameter tends to zero and porosity tends to infinity. It is seen that the effect of elastico-viscosity parameter, porosity parameter of the bounding surface has significant effect on the velocity parameter.

**Keywords:**
Elastico-viscous fluid,
Porous media,
Second order
fluids,
Spherical cross-section.

##### 2268 Unsteady Flow of an Incompressible Elastico-Viscous Fluid of Second order Type in Tube of Ellipsoidal Cross Section on a Porous Boundary

**Authors:**
Sanjay Baburao Kulkarni

**Abstract:**

Exact solution of an unsteady flow of elastico-viscous fluid through a porous media in a tube of ellipsoidal cross section under the influence of constant pressure gradient has been obtained in this paper. Initially, the flow is generated by a constant pressure gradient. After attaining the steady state, the pressure gradient is suddenly withdrawn and the resulting fluid motion in a tube of ellipsoidal cross section by taking into account of the porosity factor of the bounding surface is investigated. The problem is solved in twostages the first stage is a steady motion in tube under the influence of a constant pressure gradient, the second stage concern with an unsteady motion. The problem is solved employing separation of variables technique. The results are expressed in terms of a nondimensional porosity parameter (K) and elastico-viscosity parameter (β), which depends on the Non-Newtonian coefficient. The flow parameters are found to be identical with that of Newtonian case as elastic-viscosity parameter tends to zero and porosity tends to infinity. It is seen that the effect of elastico-viscosity parameter and the porosity parameter of the bounding surface has significant effect on the velocity parameter.

**Keywords:**
Elastico-viscous fluid,
Ellipsoidal cross-section,
Porous media,
Second order fluids.

##### 2267 Numerical Simulation of unsteady MHD Flow and Heat Transfer of a Second Grade Fluid with Viscous Dissipation and Joule Heating using Meshfree Approach

**Authors:**
R. Bhargava,
Sonam Singh

**Abstract:**

**Keywords:**
EFGM,
MHD,
Oscillatory stretching sheet,
Unsteady,
Viscoelastic

##### 2266 Unsteady MHD Flow of an Incompressible Elastico-Viscous Fluid in a Tube of Spherical Cross Section on a Porous Boundary

**Authors:**
Sanjay Baburao Kulkarni

**Abstract:**

Exact solution of an unsteady MHD flow of elasticoviscous fluid through a porous media in a tube of spherical cross section under the influence of magnetic field and constant pressure gradient has been obtained in this paper. Initially, the flow is generated by a constant pressure gradient. After attaining the steady state, the pressure gradient is suddenly withdrawn and the resulting fluid motion in a tube of spherical cross section by taking into account of the porosity factor and magnetic parameter of the bounding surface is investigated. The problem is solved in two-stages the first stage is a steady motion in tube under the influence of a constant pressure gradient, the second stage concern with an unsteady motion. The problem is solved employing separation of variables technique. The results are expressed in terms of a non-dimensional porosity parameter (K), magnetic parameter (m) and elasticoviscosity parameter (β), which depends on the Non-Newtonian coefficient. The flow parameters are found to be identical with that of Newtonian case as elastic-viscosity parameter and magnetic parameter tends to zero and porosity tends to infinity. It is seen that the effect of elastico-viscosity parameter, porosity parameter and magnetic parameter of the bounding surface has significant effect on the velocity parameter.

**Keywords:**
Elastico-viscous fluid,
Porous media,
Second order
fluids,
Spherical cross-section,
Magnetic parameter.

##### 2265 Use of Time-Depend Effects for Mixing and Separation of the Two-Phase Flows

**Authors:**
N. B. Fedosenko,
A.A Iatcenko,
S.A. Levanov

**Abstract:**

**Keywords:**
Two-phase,
mixing,
separating,
flow control

##### 2264 Numerical Investigation of Dynamic Stall over a Wind Turbine Pitching Airfoil by Using OpenFOAM

**Authors:**
Mahbod Seyednia,
Shidvash Vakilipour,
Mehran Masdari

**Abstract:**

Computations for two-dimensional flow past a stationary and harmonically pitching wind turbine airfoil at a moderate value of Reynolds number (400000) are carried out by progressively increasing the angle of attack for stationary airfoil and at fixed pitching frequencies for rotary one. The incompressible Navier-Stokes equations in conjunction with Unsteady Reynolds Average Navier-Stokes (URANS) equations for turbulence modeling are solved by OpenFOAM package to investigate the aerodynamic phenomena occurred at stationary and pitching conditions on a NACA 6-series wind turbine airfoil. The aim of this study is to enhance the accuracy of numerical simulation in predicting the aerodynamic behavior of an oscillating airfoil in OpenFOAM. Hence, for turbulence modelling, *k-ω-SST* with low-Reynolds correction is employed to capture the unsteady phenomena occurred in stationary and oscillating motion of the airfoil. Using aerodynamic and pressure coefficients along with flow patterns, the unsteady aerodynamics at pre-, near-, and post-static stall regions are analyzed in harmonically pitching airfoil, and the results are validated with the corresponding experimental data possessed by the authors. The results indicate that implementing the mentioned turbulence model leads to accurate prediction of the angle of static stall for stationary airfoil and flow separation, dynamic stall phenomenon, and reattachment of the flow on the surface of airfoil for pitching one. Due to the geometry of the studied 6-series airfoil, the vortex on the upper surface of the airfoil during upstrokes is formed at the trailing edge. Therefore, the pattern flow obtained by our numerical simulations represents the formation and change of the trailing-edge vortex at near- and post-stall regions where this process determines the dynamic stall phenomenon.

**Keywords:**
CFD,
Moderate Reynolds number,
OpenFOAM,
pitching oscillation,
unsteady aerodynamics,
wind turbine.