scholarly journals Effect of Bolts on Flow and Heat Transfer in a Rotor–Stator Disk Cavity

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
Sulfickerali Noor Mohamed ◽  
John W. Chew ◽  
Nicholas J. Hills
Keyword(s):  
Heat Transfer ◽  
Fluid Dynamics ◽  
Time Dependent ◽  
Navier Stokes ◽  
Cfd Simulations ◽  
Flow And Heat Transfer ◽  
Gap Ratio ◽  
Computational Fluid Dynamics Cfd ◽  
Dependent Flow ◽  
Insight Into

Previous studies have indicated some differences between steady computational fluid dynamics (CFD) predictions of flow in a rotor–stator disk cavity with rotating bolts compared to measurements. Recently, time-dependent CFD simulations have revealed the unsteadiness present in the flow and have given improved agreement with measurements. In this paper, unsteady Reynolds averaged Navier–Stokes (URANS) 360 deg model CFD calculations of a rotor–stator cavity with rotor bolts were performed in order to better understand the flow and heat transfer within a disk cavity previously studied experimentally by other workers. It is shown that the rotating bolts generate unsteadiness due to wake shedding which creates time-dependent flow patterns within the cavity. At low throughflow conditions, the unsteady flow significantly increases the average disk temperature. A systematic parametric study is presented giving insight into the influence of number of bolts, mass flow rate, cavity gap ratio, and the bolts-to-shroud gap ratio on the time-dependent flow within the cavity.

scholarly journals Effect of Bolts on Flow and Heat Transfer in a Rotor-Stator Disc Cavity

2016 ◽  
Author(s):  
Sulfickerali Noor Mohamed ◽  
John W. Chew ◽  
Nicholas J. Hills
Keyword(s):  
Heat Transfer ◽  
Flow Rate ◽  
Parametric Study ◽  
Time Dependent ◽  
Navier Stokes ◽  
Cfd Simulations ◽  
Flow And Heat Transfer ◽  
Gap Ratio ◽  
Dependent Flow ◽  
Insight Into

Previous studies have indicated some differences between steady CFD predictions of flow in a rotor-stator disc cavity with rotating bolts compared to measurements. Recently time-dependent CFD simulations have revealed the unsteadiness present in the flow and have given improved agreement with measurements. In this paper unsteady Reynolds averaged Navier-Stokes (URANS) 360° model CFD calculations of a rotor-stator cavity with rotor bolts were performed in order to better understand the flow and heat transfer within a disc cavity previously studied experimentally by other workers. It is shown that the rotating bolts generate unsteadiness due to wake shedding which creates time-dependent flow patterns within the cavity. At low throughflow conditions, the unsteady flow significantly increases the average disc temperature. A systematic parametric study is presented giving insight into the influence of number of bolts, mass flow rate, cavity gap ratio and the bolts-to-shroud gap ratio on the time depended flow within the cavity.

Computational Fluid Dynamics Modeling of Mixed Convection Flows in Building Enclosures

2013 ◽  
Author(s):  
Alexander Kayne ◽  
Ramesh Agarwal
Keyword(s):  
Heat Transfer ◽  
Fluid Dynamics ◽  
Experimental Data ◽  
Computational Fluid Dynamics ◽  
Mixed Convection ◽  
Turbulence Model ◽  
Numerical Algorithm ◽  
Navier Stokes ◽  
Cfd Simulations ◽  
Flow And Heat Transfer

In recent years Computational Fluid Dynamics (CFD) simulations are increasingly used to model the air circulation and temperature environment inside the rooms of residential and office buildings to gain insight into the relative energy consumptions of various HVAC systems for cooling/heating for climate control and thermal comfort. This requires accurate simulation of turbulent flow and heat transfer for various types of ventilation systems using the Reynolds-Averaged Navier-Stokes (RANS) equations of fluid dynamics. Large Eddy Simulation (LES) or Direct Numerical Simulation (DNS) of Navier-Stokes equations is computationally intensive and expensive for simulations of this kind. As a result, vast majority of CFD simulations employ RANS equations in conjunction with a turbulence model. In order to assess the modeling requirements (mesh, numerical algorithm, turbulence model etc.) for accurate simulations, it is critical to validate the calculations against the experimental data. For this purpose, we use three well known benchmark validation cases, one for natural convection in 2D closed vertical cavity, second for forced convection in a 2D rectangular cavity and the third for mixed convection in a 2D square cavity. The simulations are performed on a number of meshes of different density using a number of turbulence models. It is found that k-epsilon two-equation turbulence model with a second-order algorithm on a reasonable mesh gives the best results. This information is then used to determine the modeling requirements (mesh, numerical algorithm, turbulence model etc.) for flows in 3D enclosures with different ventilation systems. In particular two cases are considered for which the experimental data is available. These cases are (1) air flow and heat transfer in a naturally ventilated room and (2) airflow and temperature distribution in an atrium. Good agreement with the experimental data and computations of other investigators is obtained.

Evaluation of Aerodynamic Characteristics of Mega-Yacht Superstructures by CFD Simulations

2020 ◽  
Vol 36 (04) ◽  
pp. 259-270
Author(s):  
Ahmet Ziya Saydam ◽  
Serhan Gokcay ◽  
Mustafa Insel
Keyword(s):  
Aerodynamic Characteristics ◽  
Temperature Gradients ◽  
Time Dependent ◽  
Navier Stokes ◽  
Noise Generation ◽  
Velocity Data ◽  
Cfd Simulations ◽  
Recent Developments ◽  
Computational Fluid Dynamics Cfd

Air wake distribution around the superstructure of a mega-yacht is a key concern for the designer because of various reasons such as comfort expectations in recreational deck areas, self-noise generation, air pollution and temperature gradients due to exhaust interactions, and safety of helicopter operations such as landing/take off and hovering. The Reynolds-averaged Navier-Stokes (RANS) technique in computational fluid dynamics (CFD) is frequently used in studies on mega-yacht hydrodynamics and aerodynamics with satisfactory results. In this article, a case study is presented for the utilization of CFD in a mega-yacht's superstructure design. The flow field in recreational open areas has been analyzed for the increase in velocity due to the existence of the superstructure. A reduction in self-noise of the mast structure has been aimed by reducing flow separation and vorticity. Time-dependent velocity data obtained with scale-resolving simulations are presented for the evaluation of helicopter landings. The capabilities and limitations of the RANS technique are discussed along with recent developments in modeling approaches.

Characteristics of Fully Developed Flow and Heat Transfer in Channels With Varying Wall Geometry

2013 ◽  
Vol 136 (2) ◽  
Author(s):  
Abhishek G. Ramgadia ◽  
Arun K. Saha
Keyword(s):  
Heat Transfer ◽  
Time Dependent ◽  
Navier Stokes ◽  
Fully Developed Flow ◽  
Flow And Heat Transfer ◽  
Collocated Grid ◽  
Wall Profile ◽  
Energy Equations ◽  
Volume Method ◽  
Wall Geometry

Present study focuses on numerical investigation of fully developed flow and heat transfer through three channels having sine-shaped, triangle-shaped, and arc-shaped wall profiles. All computations are performed at Reynolds number of 600. Finite volume method on collocated grid is used to solve the time-dependent Navier–Stokes and energy equations in primitive variable form. For all the geometries considered in the study, the ratios Hmin/Hmax and L/a are kept fixed to 0.4 and 8.0, respectively. The thermal performances of all the three wall configurations are assessed using integral parameters as well as instantaneous, time-averaged and fluctuating flow fields. The geometry with the sinusoidal-shaped wall profile is found to produce the best thermal properties as compared to the triangle-shaped and the arc-shaped profiles though the obtained heat transfer is the highest for the arc-shaped geometry.

Axisymmetric Stagnation-Point Flow and Heat Transfer of a Viscous Fluid on a Moving Cylinder With Time-Dependent Axial Velocity and Uniform Transpiration

2004 ◽  
Vol 126 (6) ◽  
pp. 997-1005 ◽  
Author(s):  
R. Saleh ◽  
A. B. Rahimi
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Axial Velocity ◽  
Time Dependent ◽  
Navier Stokes ◽  
Flow And Heat Transfer ◽  
Moving Cylinder ◽  
Self Similar ◽  
Suction Rate ◽  
Axial Speed

The unsteady viscous flow and heat transfer in the vicinity of an axisymmetric stagnation point of an infinite moving cylinder with time-dependent axial velocity and with uniform normal transpiration Uo are investigated. The impinging free stream is steady and with a constant strain rate k¯. An exact solution of the Navier–Stokes equations and energy equation is derived in this problem. A reduction of these equations is obtained by use of appropriate transformations for the most general case when the transpiration rate is also time-dependent but results are presented only for uniform values of this quantity. The general self-similar solution is obtained when the axial velocity of the cylinder and its wall temperature or its wall heat flux vary as specified time-dependent functions. In particular, the cylinder may move with constant speed, with exponentially increasing–decreasing axial velocity, with harmonically varying axial speed, or with accelerating–decelerating oscillatory axial speed. For self-similar flow, the surface temperature or its surface heat flux must have the same types of behavior as the cylinder motion. For completeness, sample semisimilar solutions of the unsteady Navier–Stokes and energy equations have been obtained numerically using a finite-difference scheme. Some of these solutions are presented for special cases when the time-dependent axial velocity of the cylinder is a step-function, and a ramp function. All the solutions above are presented for Reynolds numbers, Re=ka¯2/2υ, ranging from 0.1 to 100 for different values of dimensionless transpiration rate, S=Uo/ka¯, where a is cylinder radius and υ is kinematic viscosity of the fluid. Absolute value of the shear-stresses corresponding to all the cases increase with the increase of Reynolds number and suction rate. The maximum value of the shear- stress increases with increasing oscillation frequency and amplitude. An interesting result is obtained in which a cylinder moving with certain exponential axial velocity function at any particular value of Reynolds number and suction rate is axially stress-free. The heat transfer coefficient increases with the increasing suction rate, Reynolds number, Prandtl number, oscillation frequency and amplitude. Interesting means of cooling and heating processes of cylinder surface are obtained using different rates of transpiration. It is shown that a cylinder with certain type of exponential wall temperature exposed to a temperature difference has no heat transfer.

Axisymmetric Stagnation—Point Flow and Heat Transfer of a Viscous Fluid on a Rotating Cylinder With Time-Dependent Angular Velocity and Uniform Transpiration

2006 ◽  
Vol 129 (1) ◽  
pp. 106-115 ◽  
Author(s):  
A. B. Rahimi ◽  
R. Saleh
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Reynolds Number ◽  
Angular Velocity ◽  
Stokes Equations ◽  
Time Dependent ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Flow And Heat Transfer ◽  
Self Similar

The unsteady viscous flow and heat transfer in the vicinity of an axisymmetric stagnation point of an infinite rotating circular cylinder with transpiration U0 are investigated when the angular velocity and wall temperature or wall heat flux all vary arbitrarily with time. The free stream is steady and with a strain rate of Γ. An exact solution of the Navier-Stokes equations and energy equation is derived in this problem. A reduction of these equations is obtained by the use of appropriate transformations for the most general case when the transpiration rate is also time-dependent but results are presented only for uniform values of this quantity. The general self-similar solution is obtained when the angular velocity of the cylinder and its wall temperature or its wall heat flux vary as specified time-dependent functions. In particular, the cylinder may rotate with constant speed, with exponentially increasing/decreasing angular velocity, with harmonically varying rotation speed, or with accelerating/decelerating oscillatory angular speed. For self-similar flow, the surface temperature or its surface heat flux must have the same types of behavior as the cylinder motion. For completeness, sample semi-similar solutions of the unsteady Navier-Stokes equations have been obtained numerically using a finite-difference scheme. Some of these solutions are presented for special cases when the time-dependent rotation velocity of the cylinder is, for example, a step-function. All the solutions above are presented for Reynolds numbers, Re=Γa2∕2υ, ranging from 0.1 to 1000 for different values of Prandtl number and for selected values of dimensionless transpiration rate, S=U0∕Γa, where a is cylinder radius and υ is kinematic viscosity of the fluid. Dimensionless shear stresses corresponding to all the cases increase with the increase of Reynolds number and suction rate. The maximum value of the shear stress increases with increasing oscillation frequency and amplitude. An interesting result is obtained in which a cylinder rotating with certain exponential angular velocity function and at particular value of Reynolds number is azimuthally stress-free. Heat transfer is independent of cylinder rotation and its coefficient increases with the increasing suction rate, Reynolds number, and Prandtl number. Interesting means of cooling and heating processes of cylinder surface are obtained using different rates of transpiration.

Assessment of Heat Transfer and Airflow Characteristics in Air-Conditioned Room: 3D Time-Dependent Model

2004 ◽  
Author(s):  
Ramiz Kameel ◽  
Essam E. Khalil
Keyword(s):  
Heat Transfer ◽  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Time Dependent ◽  
Design System ◽  
Cfd Model ◽  
Dependent Model ◽  
Recirculation Zones ◽  
Computational Fluid Dynamics Cfd ◽  
Time Dependent Model

Airflow characteristics in ventilated and air-conditioned spaces play an important role to attain comfort and hygiene conditions. This paper utilizes a 3D time-dependent Computational Fluid Dynamics (CFD) model to assess the airflow characteristics in different air-conditioned spaces. It is found that the optimum airside design system can be attained, if the airflow is directed to pass all the enclosure areas before the extraction. Still most of these factors and evaluation indices have the shortage of adequately describe the influence of the recirculation zones on the occupancy zone and also on the fresh supplied air. The model of evaluation should assess the airflow characteristics in any enclosure according to its position in the enclosure and the expected target of it along its pass to the extraction.

Numerical Simulation of Flow and Heat Transfer with Large-Eddy Simulation in a Mixing T-Junction

2012 ◽  
Vol 152-154 ◽  
pp. 1319-1324
Author(s):  
Tao Lu ◽  
Xing Guo Zhu ◽  
Ping Wang ◽  
Wei Yyu Zhu
Keyword(s):  
Heat Transfer ◽  
Fluid Dynamics ◽  
Large Eddy Simulation ◽  
Root Mean Square ◽  
Mean Square ◽  
Main Duct ◽  
Eddy Simulation ◽  
Flow And Heat Transfer ◽  
Large Eddy ◽  
Computational Fluid Dynamics Cfd

In the present paper, large-eddy simulation (LES) based on commercial computational fluid dynamics (CFD) software FLUENT for prediction of flow and heat transfer in a mixing T-junction was completed. Mean and root mean square (RMS) temperature and velocity were defined to describe the distributions and fluctuations of temperature and velocity. Numerical results indicate that profiles between symmetrical planes are almost same and the root mean square temperature and velocity close to the center of the main duct in the downstream are larger than those near the main duct wall. The prediction of the fluctuations of temperature and velocity is significant to understand the knowledge of the cause of thermal fatigue in a mixing T-junction.

Airflow and Cooling in a Data Center

2010 ◽  
Vol 132 (7) ◽  
Author(s):  
Suhas V. Patankar
Keyword(s):  
Fluid Dynamics ◽  
Data Center ◽  
Cfd Simulations ◽  
Flow Rates ◽  
Factors Affecting ◽  
Hot Air ◽  
Airflow Distribution ◽  
Computational Fluid Dynamics Cfd ◽  
Cooling Air ◽  
Insight Into

This paper deals with the distribution of airflow and the resulting cooling in a data center. First, the cooling challenge is described and the concept of a raised-floor data center is introduced. In this arrangement, cooling air is supplied through perforated tiles. The flow rates of the cooling air must meet the cooling requirements of the computer servers placed next to the tiles. These airflow rates are governed primarily by the pressure distribution under the raised floor. Thus, the key to modifying the flow rates is to influence the flow field in the under-floor plenum. Computational fluid dynamics (CFD) is used to provide insight into various factors affecting the airflow distribution and the corresponding cooling. A number of ways of controlling the airflow distribution are explored. Then attention is turned to the above-floor space, where the focus is on preventing the hot air from entering the inlets of computer serves. Different strategies for doing this are considered. The paper includes a number of comparisons of measurements with the results of CFD simulations.

Maximization of Solar Gains of an Air Collector by Simulations

2013 ◽  
Vol 284-287 ◽  
pp. 483-487 ◽  
Author(s):  
Ondrej Sikula ◽  
Vit Merka ◽  
Jiri Hirs ◽  
Josef Plášek
Keyword(s):  
Heat Transfer ◽  
Solar Energy ◽  
Solar Collector ◽  
Cfd Simulations ◽  
Ansys Fluent ◽  
Operation Conditions ◽  
Flow And Heat Transfer ◽  
Solar Air Collector ◽  
Computational Fluid Dynamics Cfd ◽  
The Impact

The paper deals with numerical simulations of the impact of design, shading, positioning and orientation of a solar air collector an efficiency of exploitation of solar energy. The solar collector is used to preheat of an air, which then is supplied into the building. There are various requirements for solar air collectors. We are focused on maximization of solar energy gain by optimizing geometry, orientation and positioning of a solar air collector. To achieve the desired objective was a combination of two methods used. The firs one is Computational Fluid Dynamics (CFD) simulations of flow and heat transfer by convection, conduction and radiation in software ANSYS Fluent. The second one is the numerical simulation of the annual operations of the collector in the software BSim. The result of this work is an optimal design and operation conditions of the air collector.

Sign in / Sign up

Export Citation Format

Share Document