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The purpose of this paper is to study numerically and experimentally incompressible Newtonian flow in a three‐dimensional cylindrical branching channel.

The flow configuration studied in the present investigation is such that a fully developed laminar flow enters an abruptly expanded cylinder and the flow leaves this cylinder by two identical cylindrical outlet branch pipes. A numerical analysis was performed by developing a three‐dimensional numerical code using the highly simplified marker and cell method. Representative velocities in the flow field are recorded by Laser Doppler Velocimeter measurements and volume flow rate from each outlet branch pipe is measured. Flow visualization in representative symmetrical planes is also carried out. Comparisons of numerical predictions and experimental data are presented and the reasonable agreement between the numerical and experimental results is encouraging.

The flow field in the three‐dimensional cylindrical branching channel is clarified within the range of laminar flow. The characteristics of the branch flow rate are obtained and show that there exist two distinct domains of strong asymmetric flow distribution from the outlet branch pipes, depending on the Reynolds numbers. It is further observed that the flow became time periodic as the Reynolds number is increased. It becomes apparent that the swirl flow component plays a key role in the flow phenomena.

The present investigation sheds light on the three‐dimensionality in the prevailing flow field for various inlet Reynolds numbers in the laminar flow range. Flow rate deflection characteristics in a three‐dimensional cylindrical branching channel are also obtained.

This paper aims to present the designing and investigating various types of impulse blade profiles to find the optimal profile that has better performance than the first or original blade. The studied model is a turbine with an output power below 1 MW and a large pressure ratio up to 20, which is used to gain relatively high specific work output. As a result of its low mass flow rate, the turbine is used under partial-admission conditions. The turbine’s stator is a group of convergence–divergence nozzles that provide supersonic flow.

More than 10 types of two-dimensional blade profiles were designed using the developed preliminary design calculations and numerical analysis. The numerical results are validated using the existing experimental results. Finally, the case with improved performance is introduced as the final optimum case.

It was found that the performance parameters such as efficiency, power and torque are increased by more than 8% in the selected best model, in comparison with the original model. Moreover, the total pressure loss is 12% decreased for the selected model. Finally, the selected profile with superior performance is proposed.

Simultaneous numerical tests are conducted to examine the interaction of different supersonic blade profiles with the partially injected flow to the rotor.

The purpose of this paper is to investigate, experimentally and numerically, the pressure pulse characteristics and unsteady flow behavior in a Francis turbine runner for moderate flow heads. The pressure pulses in the runner blade passage were predicted numerically for both moderate and high heads. The calculations were used to partition the turbine operating regions and to clarify the various for the unsteady flow behavior, especially the blade channel vortex in the runner.

Experimental and numerical analyses of pressure pulse characteristics at moderate flow heads in a Francis turbine runner were then extended to high heads through numerical modeling with 3D unsteady numerical simulations performed for a number of operating conditions. The unsteady Reynolds‐averaged Navier‐Stokes equations with the k‐ω‐based shear stress transport turbulence model were used to model the unsteady flow within the entire flow passage of a Francis turbine.

The dominate frequency of the predicted pressure pulses at runner inlet agree with the experimental results in the head cover at moderate flow heads. The influence of the blade passing frequency causes the simulated peak‐to‐peak amplitudes in the runner inlet to be larger than in the head cover. The measured and predicted pressure pulses at different positions along the runner are comparable. At the most unstable operating condition of 0.5a₀ guide vane opening, the pressure pulses in the runner blade passage are due to the blade channel vortex and the rotor‐stator interference. The predictions show that the frequency of the blade channel vortex is relatively low and it changes with the operating conditions.

The paper describes a study which experimentally and numerically investigated the pressure pulses characteristics in a Francis turbine runner at moderate flow heads. The pulse characteristics and unsteady flow behavior due to the blade channel vortex in the runner at high heads were investigated numerically, with the turbine operating regions then partitioned to identify safe operating regions.

The purpose of this paper is to study the effects of nonlinear partial slip on the walls for steady flow and heat transfer of an incompressible, thermodynamically compatible third grade fluid in a channel. The principal question the authors address in this paper is in regard to the applicability of the no‐slip condition at a solid‐liquid boundary. The authors present the effects of slip, magnetohydrodynamics (MHD) and heat transfer for the plane Couette, plane Poiseuille and plane Couette‐Poiseuille flows in a homogeneous and thermodynamically compatible third grade fluid. The problem of a non‐Newtonian plane Couette flow, fully developed plane Poiseuille flow and Couette‐Poiseuille flow are investigated.

The present investigation is an attempt to study the effects of nonlinear partial slip on the walls for steady flow and heat transfer of an incompressible, thermodynamically compatible third grade fluid in a channel. A very effective and higher order numerical scheme is used to solve the resulting system of nonlinear differential equations with nonlinear boundary conditions. Numerical solutions are obtained by solving nonlinear ordinary differential equations using Chebyshev spectral method.

Due to the nonlinear and highly complicated nature of the governing equations and boundary conditions, finding an analytical or numerical solution is not easy. The authors obtained numerical solutions of the coupled nonlinear ordinary differential equations with nonlinear boundary conditions using higher order Chebyshev spectral collocation method. Spectral methods are proven to offer a superior intrinsic accuracy for derivative calculations.

To the best of the authors' knowledge, no such analysis is available in the literature which can describe the heat transfer, MHD and slip effects simultaneously on the flows of the non‐Newtonian fluids.

With aims to increase the aerodynamic efficiency of aerodynamic surfaces, study on flow control over these surfaces has gained importance. With the addition of flow control devices such as synthetic jets and vortex generators, the flow characteristics can be modified over the surface and, at the same time, enhance the performance of the body. One such flow control device is the tubercle. Inspired by the humpback whale’s flippers, these leading-edge serrations have improved the aerodynamic efficiency and the lift characteristics of airfoils and wings. This paper aims to discusses in detail the flow physics associated with tubercles and their effect on swept wings.

This study involves a series of experimental and numerical analyses that have been performed on four different wing configurations, with four different sweep angles corresponding to 0°, 10°, 20° and 30° at a low Reynolds number corresponding to Re_c=100,000.

Results indicate that the effect of tubercles diminishes with an increase in wing sweep. A significant performance enhancement was observed in the stall and post-stall regions. The addition of tubercles led to a smooth post-stall lift characteristic compared to the sudden loss in the lift with regular wings. Among the four different wings under observation, it was found that tubercles were most effective on the 0° configuration (no sweep), showing a 10.8% increment in maximum lift and a 38.5% increase in the average lift generated in the post-stall region. Tubercles were least effective on 30° configuration. Furthermore, with an increase in wing sweep, co-rotating vortices were distinctly observed rather than counter-rotating vortices.

While extensive numerical and experimental studies have been performed on straight wings with tubercles, studies on the tubercle effect on swept wings at low Reynolds number are minimal and mainly experimental in nature. This study uses numerical methods to explore the complex flow physics associated with tubercles and their implementation on swept wings. This study can be used as an introductory study to implement passive flow control devices in the low Reynolds number regime.

In this paper, experimental and numerical results of a lambda wing have been compared. The purpose of this paper is to study the behaviour of lambda wings using a CFD tool and to consider different numerical models to obtain the most accurate results. As far as the consideration of numerical methods is concerned, the main focus is on the evaluation of computational methods for an accurate prediction of contingent leading edge vortices’ path and the flow separation occurring because of the burst of these vortices on the wing.

Experimental tests are performed in a closed-circuit wind tunnel at the Reynolds number of 6 × 105 and angles of attack (AOA) ranging from 0 to 10 degrees. Investigated turbulence models in this study are Reynolds Averaged Navior–Stokes (RANS) models in a steady state. To compare the accuracy of the turbulence models with respect to experimental results, sensitivity study of these models has been plotted in bar charts.

The results illustrate that the leading edge vortex on this lambda wing is unstable and disappears soon. The effect of this disappearance is obvious by an increase in local drag coefficient in the junction of inner and outer wings. Streamlines on the upper surface of the wing show that at AOA higher than 8 degrees, the absence of an intense leading edge vortex leads to a local flow separation on the outer wing and a reverse in the flow.

Results obtained from the behaviour study of transition (TSS) turbulence model are more compatible with experimental findings. This model predicts the drag coefficient of the wing with the highest accuracy. Of all considered turbulence models, the Spalart model was not able to accurately predict the non-linearity of drag and pitching moment coefficients. Except for the TSS turbulence model, all other models are unable to predict the aerodynamic coefficients corresponding to AOA higher than 10 degrees.

The presented results in this paper include lift, drag and pitching moment coefficients in various AOA and also the distribution of aerodynamic coefficients along the span.

The presented results include lift, drag and pitching moment coefficients in various AOA and also aerodynamic coefficients distribution along the span.

The aim of this article is to present the results of a parametric analysis of the entropy generation due to mixed convection in the entry‐developing region between two differentially heated isothermal vertical plates.

The entropy generation was estimated via a numerical solution of the mass, momentum and energy conservation equations governing the flow and heat transfer in the vertical channel between the two parallel plates. The resultant temperature and velocity profiles were used to estimate the entropy generation and other heat transfer parameters over a wide range of the operating parameters. The investigated parameters include the buoyancy parameter (Gr/Re), Eckert number (Ec), Reynolds number (Re), Prandtl number (Pr) and the ratio of the dimensionless temperature of the two plates (θ_T).

The optimum values of the buoyancy parameter (Gr/Re) optimum at which the entropy generation assumes its minimum for the problem under consideration have been obtained numerically and presented over a wide range of the other operating parameters. The effect of the other operating parameters on the entropy generation is presented and discussed as well.

The results of this investigation are limited to the geometry of vertical channel parallel plates under isothermal boundary conditions. However, the concept of minimization of entropy generation via controlling the buoyancy parameter is applicable for any other geometry under any other thermal boundary conditions.

The results presented in this paper can be used for optimum designs of heat transfer equipment based on the principle of entropy generation minimization with particular focus on the optimum design of plate and frame heat exchanger and the optimization of electronic packages and stacked packaging of laminar‐convection‐cooled printed circuits.

This paper introduces the entropy generation minimization via controlling the operating parameters and clearly identifies the optimum buoyancy parameter (Gr/Re) at which entropy generation assumes its minimum under different operating conditions.

The purpose of this paper is to describe how the hydraulic performance and pressure fluctuations in the entire flow passage of a Francis turbine were predicted numerically for the highest head. The calculations are used to partition the turbine operating regions and to clarify the unsteady flow behavior in the entire flow passage including the blade channel vortex in the runner and vortex rope in the draft tube.

Three‐dimensional unsteady numerical simulations were performed for a number of operating conditions at the highest head. The unsteady Reynolds‐averaged Navier‐Stokes equations with the k‐ω based SST turbulence model were solved to model the unsteady flow within the entire flow passage of a Francis turbine.

The predicted pressure fluctuations in the draft tube agree well with the experimental results at low heads. However the peak‐to‐peak amplitudes in the spiral case are not as well predicted so the calculation domain and the inlet boundary conditions need to be improved. The unsteady simulation results are better than the steady‐state results. At the most unstable operating condition of case a0.5h1.26, the pulse in the flow passage is due to the rotor‐stator interference between the runner and the guide vanes, the blade channel vortex in the runner blade passage and the vortex rope in the draft tube.

This study investigates the characteristics of the dominant unsteady flow frequencies in different parts of the turbine for various guide vane openings at the highest head. The unsteady flow patterns in the turbine, including the blade channel vortex in the runner and the helical vortex rope in the draft tube, are classified numerically, and the turbine operating regions are partitioned to identify safe operating regions.

This paper aims to use a fractional constitutive model with a nonlocal velocity gradient for replacing the nonlinear constitutive model to characterize its complex rheological behavior, where non-linear characteristics exist, for example, the inherent viscous behavior of the crude oil. The feasibility and flexibility of the fractional model are tested via a case study of non-Newtonian fluid. The finite element method is non-Newtonian used to numerically solve both momentum equation and energy equation to describe the fluid flow and convection heat transfer process.

This paper provides a comprehensive theoretical and numerical study of flow and heat transfer of non-Newtonian fluids in a pipe based on the fractional constitutive model. Contrary to fractional order a, the rheological property of non-Newtonian fluid changes from shear-thinning to shear-thickening with the increase of power-law index n, therefore the flow and heat transfer are hindered to some extent.

This paper discusses two dimensionless parameters on flow regime and thermal patterns, including Reynolds number (Re) and Nusselt number (Nu) in evaluating the flow rate and heat transfer rate. Analysis results show that the viscosity of the non-Newtonian fluid decreases with the rheological index (order α) increasing. While large fractional (order α) corresponds to the enhancement of heat transfer capacity.

First, it is observed that the increase of the Re results in an increase of the local Nusselt number (Nul). It means the heat transfer enhancement ratio increases with Re. Meanwhile, the increasement of the Nul indicating the enhancement in the heat transfer coefficient, produces a higher speed flow of crude oil.

This study presents a new numerical investigation on characteristics of steady-state pipe flow and forced convection heat transfer by using a fractional constitutive model. The influences of various non-dimensional characteristic parameters of fluid on the velocity and temperature fields are analyzed in detail.

The purpose of this current study is to identify the optimal stable position of airship, with reference to spatial variation of atmospheric wind flow, so as to reduce the vibrations and thus aid in the development of control mechanism of airship dynamics.

Study of uniform flow under steady‐state conditions was carried out through the measurements of pressure and velocity in a wind tunnel at low Mach numbers on airship model (in order of size, 1:13) inclined to the uniform air stream at various angles. The measurements have been made for a range of angles of incidence, in both vertical and horizontal planes, with a Reynolds number, based on the free stream velocity and a body cross‐sectional dimension, of order of four and six, respectively. Steady‐state numerical simulations were performed, serving comparative investigation with experimental data for the specific case of the model inclined to the free stream, with orientation of side‐slip (yaw) angle β=0 and angle of attack (pitch) α=0.

The numerical results showed similar trend as found by experimental analysis. In this study, several factors such as the pressure (C_p), lift (C_L), drag (C_D) coefficients, pressure and air velocity were taken into account for comparative analysis. The analysis paved the way in identification of constructively stable position of airship model with orientation of β=0 and α=0, with respect to air flow direction.

The current findings aid in the development of control mechanism of airship dynamics.

The experimental analysis of the airship model is presented along with computational fluid dynamics analysis of optimised shape of airship model in different orientations with respect to direction of airflow.