Influence of Bed Size on the Flow Characteristics and Porosity of Randomly Packed Beds of Spheres

1973 ◽  
Vol 40 (3) ◽  
pp. 655-660 ◽  
Author(s):  
G. S. Beavers ◽  
E. M. Sparrow ◽  
D. E. Rodenz
Keyword(s):  
Rectangular Cross Section ◽  
Flow Characteristics ◽  
Operating Conditions ◽  
Darcy Law ◽  
Equivalent Diameter ◽  
Packed Beds ◽  
Sphere Diameter ◽  
Number Range ◽  
Inertia Term ◽  
Bed Porosity

Experiments were performed to investigate the flow characteristics and porosity of randomly packed beds of glass spheres for conditions where the bed size cannot be regarded as infinitely large compared with the sphere size. The operating conditions of the flow experiments extended over a Reynolds number range for which the flow was governed by the Forchheimer extension of the linear Darcy law. The influence of the bed bounding walls on the permeability, on the coefficient of the Forchheimer inertia term, and on the porosity, was studied by using beds of rectangular cross section. It was found that the permeability was not apparently influenced by the bounding walls when the equivalent diameter of the bed was greater than 12 times the sphere diameter, whereas the coefficient of the inertia term was affected by the presence of the walls for bed equivalent diameters as high as 40 sphere diameters. The porosity of the beds was not influenced by the bed size for values of the bed equivalent diameter greater than 15 sphere diameters. When the large-bed porosity value was used with the Carman-Kozeny relationship for the permeability as a function of sphere diameter, an excellent representation of accumulated experimental data was attained.

Unsteady simulations of migration and deposition of fly-ash particles in the first-stage turbine of an aero-engine

2021 ◽  
pp. 1-21
Author(s):  
Z. Hao ◽  
X. Yang ◽  
Z. Feng
Keyword(s):  
Fly Ash ◽  
Film Cooling ◽  
Particle Deposition ◽  
Flow Characteristics ◽  
Leading Edge ◽  
Velocity Model ◽  
Operating Conditions ◽  
Inlet Temperature ◽  
Internal Cooling ◽  
Aero Engine

Abstract Particulate deposits in aero-engine turbines change the profile of blades, increase the blade surface roughness and block internal cooling channels and film cooling holes, which generally leads to the degradation of aerodynamic and cooling performance. To reveal particle deposition effects in the turbine, unsteady simulations were performed by investigating the migration patterns and deposition characteristics of the particle contaminant in a one-stage, high-pressure turbine of an aero-engine. Two typical operating conditions of the aero-engine, i.e. high-temperature take-off and economic cruise, were discussed, and the effects of particle size on the migration and deposition of fly-ash particles were demonstrated. A critical velocity model was applied to predict particle deposition. Comparisons between the stator and rotor were made by presenting the concentration and trajectory of the particles and the resulting deposition patterns on the aerofoil surfaces. Results show that the migration and deposition of the particles in the stator passage is dominated by the flow characteristics of fluid and the property of particles. In the subsequential rotor passage, in addition to these factors, particles are also affected by the stator–rotor interaction and the interference between rotors. With higher inlet temperature and larger diameter of the particle, the quantity of deposits increases and the deposition is distributed mainly on the Pressure Side (PS) and the Leading Edge (LE) of the aerofoil.

scholarly journals Development of Hybrid Airlift-Jet Pump with Its Performance Analysis

2018 ◽  
Vol 8 (9) ◽  
pp. 1413 ◽  
Author(s):  
Dan Yao ◽  
Kwongi Lee ◽  
Minho Ha ◽  
Cheolung Cheong ◽  
Inhiug Lee
Keyword(s):  
Boundary Conditions ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Stokes Equations ◽  
Flow Characteristics ◽  
Operating Conditions ◽  
Navier Stokes ◽  
Jet Pump ◽  
Two Phase

A new pump, called the hybrid airlift-jet pump, is developed by reinforcing the advantages and minimizing the demerits of airlift and jet pumps. First, a basic design of the hybrid airlift-jet pump is schematically presented. Subsequently, its performance characteristics are numerically investigated by varying the operating conditions of the airlift and jet parts in the hybrid pump. The compressible unsteady Reynolds-averaged Navier-Stokes equations, combined with the homogeneous mixture model for multiphase flow, are used as the governing equations for the two-phase flow in the hybrid pump. The pressure-based methods combined with the Pressure-Implicit with Splitting of Operators (PISO) algorithm are used as the computational fluid dynamics techniques. The validity of the present numerical methods is confirmed by comparing the predicted mass flow rate with the measured ones. In total, 18 simulation cases that are designed to represent the various operating conditions of the hybrid pump are investigated: eight of these cases belong to the operating conditions of only the jet part with different air and water inlet boundary conditions, and the remaining ten cases belong to the operating conditions of both the airlift and jet parts with different air and water inlet boundary conditions. The mass flow rate and the efficiency are compared for each case. For further investigation into the detailed flow characteristics, the pressure and velocity distributions of the mixture in a primary pipe are compared. Furthermore, a periodic fluctuation of the water flow in the mass flow rate is found and analyzed. Our results show that the performance of the jet or airlift pump can be enhanced by combining the operating principles of two pumps into the hybrid airlift-jet pump, newly proposed in the present study.

Numerical Simulation on Heat Transfer and Fluid Flow Characteristics of Arrays With Nonuniform Plate Length Positioned Obliquely to the Flow Direction

1998 ◽  
Vol 120 (4) ◽  
pp. 991-998 ◽  
Author(s):  
L. B. Wang ◽  
G. D. Jiang ◽  
W. Q. Tao ◽  
H. Ozoe
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Flow Direction ◽  
Flow Characteristics ◽  
Numerical Results ◽  
The Body ◽  
Number Range ◽  
Plate Length ◽  
Nonuniform Plate ◽  
Short Plate

The periodically fully developed laminar heat transfer and pressure drop of arrays with nonuniform plate length aligned at an angle (25 deg) to air direction have been investigated by numerical analysis in the Reynolds number range of 50–1700. The body-fitted coordinate system generated by the multisurface method was adopted to retain the corresponding periodic relation of the lines in physical and computational domains. The computations were carried out just in one cycle. Numerical results show that both the heat transfer and pressure drop increase with the increase in the length ratio of the long plate to the short plate, and decrease with the decrease in the ratio of transverse pitch to the longitudinal pitch. The numerical results exhibit good agreement with available experimental data.

scholarly journals Investigating the In-Flow Characteristics of Multi-Operation Conditions of Cross-Flow Fan in Air Conditioning Systems

Processes ◽  
2019 ◽  
Vol 7 (12) ◽  
pp. 959
Author(s):  
Weijie Zhang ◽  
Jianping Yuan ◽  
Qiaorui Si ◽  
Yanxia Fu
Keyword(s):  
Pressure Distribution ◽  
Flow Rate ◽  
Total Pressure ◽  
Air Conditioning ◽  
Pressure Pulsation ◽  
Flow Characteristics ◽  
Cross Flow ◽  
Operating Conditions ◽  
Aerodynamic Noise ◽  
Cross Flow Fan

Cross-flow fans are widely used in numerous applications such as low-pressure ventilation, household appliances, laser instruments, and air-conditioning equipment. Cross-flow fans have superior characteristics, including simple structure, small size, stable airflow, high dynamic pressure coefficient, and low noise. In the present study, numerical simulation and experimental research were carried out to study the unique secondary flow and eccentric vortex flow characteristics of the internal flow field in multi-operating conditions. To this end the vorticity and the circumferential pressure distribution in the air duct are obtained based on the performed experiments and the correlation between spectral characteristics of multiple operating conditions and the inflow state is established. The obtained results show that when the area of the airflow passage decreases while the area of the eccentric vortex area gradually increases, then the airflow of the cross-flow fan decreases, the outlet expands, and the flow pattern uniformity reduces. It was found that wakes form in the vicinity of the blade and the tail of the volute tongue, which generate pressure pulsation, and aerodynamic noise. The pressure distribution along the inner circumference shows that the total minimum pressure appears in the eccentric vortex near the volute tongue and the volute returns near the zone. Moreover, it was found that the total pressure near the eccentric vortex is significantly smaller than that of the main flow zone. As the flow rate decreases, the pressure pulsation amplitude of the eccentric vortex region significantly increases, while the static and total pressure pulsation amplitudes are gradually increased. Close to the eccentric vortex on the inner side of the blade in the volute tongue area, total pressure is low, total pressure on the outside of the blade is not affected, and pressure difference between the inner and outer sides is large. When the flow rate of the cross-flow fan is 0.4 Qd, there is no obvious peak at the harmonic frequency of the blade passage frequency. This shows that the aerodynamic noise is caused by the main unstable flow.

scholarly journals Development of an assembly for the realization of a transducer able to operate at very high temperatures

2019 ◽  
Vol 283 ◽  
pp. 07011
Author(s):  
Didier Flotté ◽  
David Macel ◽  
Abd Ennour Bouzenad ◽  
Frédéric Navacchia
Keyword(s):  
Stainless Steel ◽  
High Temperatures ◽  
Nuclear Reactor ◽  
New Technology ◽  
Operating Conditions ◽  
Equivalent Diameter ◽  
Assembly Technique ◽  
The One ◽  
Piezoelectric Disc ◽  
Very High

Monitoring the operation of the latest-generation nuclear reactor requires ultrasonic transducers able to operate at very high temperatures (> 600°C). To achieve this, CEA has requested from “Institut de Soudure” to help developing a new technology for these transducers compared to the one previously developed. This began with the development of a reliable assembly technique between a lithium niobate piezoelectric disc whose Curie temperature exceeds 1100°C and stainless steel discs. The chosen solution was to braze the niobate disc between two stainless steel discs. Parallel to this development, it was also necessary to develop a NDE procedure to verify the quality of the brazing assemblies. This development began with a simulation of immersion ultrasonic testing of the assemblies. The constraints were to be able to control the two brazed interfaces from the same access face, with the possibility of detecting and dimensioning defects with an equivalent diameter of 0.25 mm. This phase is important to define the optimal transducer with the associated operating conditions. The first assemblies validated the preliminary choices. To exploit the cartographies obtained, a signal processing procedure was developed. This enabled an automatic characterization of the indications observed. However, the analysis of the signals observed proved to be more complex than the one predicted by the simulation. Once the origin of the various observed signals was identified it was then possible to define windows allowing the construction of the cartographies to analyze. In case of a good quality assembly, it was possible to qualify the generated beam and to image it in the focal plane but with an observed signal having a very low damping. These first encouraging results, however, show that there is still some validation and development work to increase the sensitivity of the developed translator and its damping.

Assessment of Scavenge Efficiency for a Helicopter Particle Separation System

2011 ◽  
Author(s):  
Leiyong Jiang ◽  
Michael Benner ◽  
Jeff Bird
Keyword(s):  
Shape Factor ◽  
Flow Characteristics ◽  
Particle Separation ◽  
Operating Conditions ◽  
Separation Mechanism ◽  
Separation System ◽  
Small Particles ◽  
Inlet Velocity ◽  
Separation Systems ◽  
Large Particles

The effectiveness of a typical helicopter particle separation system has been numerically assessed at practical operating conditions and sand environments for various scenarios. The particle separation mechanism and its limitation are revealed by the flow characteristics and particle trajectories in the flow-field. The separation-by-inertia concept is effective for removing large particles, but problematic for small particles of diameter (d) ≤ 36μm. The particle size, shape factor, and rebound characteristics exert substantial effects on particle scavenge efficiency. On the other hand, the effects of gravity, particle inlet velocity, inlet mass distribution, and engine operating conditions on scavenge efficiency are minor or limited for the configurations and operating conditions considered in the present study. In addition, a few suggestions for further investigation on engine particle separation systems are included.

Practical Slot Configurations for Turbine Film Cooling Applications

2009 ◽  
Author(s):  
Joshua E. Bruce-Black ◽  
Frederick T. Davidson ◽  
David G. Bogard ◽  
David R. Johns
Keyword(s):  
Film Cooling ◽  
Flow Characteristics ◽  
Suction Side ◽  
Operating Conditions ◽  
Coolant Flow ◽  
Film Cooling Effectiveness ◽  
Diffusion Technique ◽  
Turbine Vane ◽  
Structural Weakness ◽  
Turbine Component

Turbine component film cooling is most effective when using a continuous slot to introduce coolant to the surface. However, this is not practical due to the structural weakness that would be inherent with a continuous slot. In this study, several slot-like designs are investigated to establish the film cooling effectiveness. These slot configurations extended only a partial distance through the simulated turbine vane wall, and were fed with impinging cylindrical holes. The configurations were studied on the suction side of a scaled-up turbine vane. In this study varying slot widths, discrete and continuous slots, and diffusing the coolant flow within the slot prior to it being emitted onto the surface of the vane were investigated. Rows of discrete round and shaped holes were also tested for comparison with the slots. The study of varying slot geometries showed that decreasing the width of the slots led to a substantial increase in adiabatic effectiveness. An internal coolant diffusion technique showed promise by maintaining performance levels while potentially providing a design configuration that more readily meets structural demands in real world operating conditions. The coolant flow characteristics were also studied through the use of thermal profiles measurements. These thermal profiles showed significant mainstream ingestion on the top surface of the slot prior to the coolant emitting onto the surface of the vane.

PIV Measurements in Diffuser of the Radial Pump

2015 ◽  
Author(s):  
Sung Yong Jung ◽  
Young Uk Min ◽  
Kyung Lok Lee
Keyword(s):  
High Speed ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Operating Conditions ◽  
Internal Flows ◽  
Piv Measurements ◽  
Image Velocimetry ◽  
Acquisition Device ◽  
Field Information ◽  
Radial Pump

The performance characteristics of the radial pump commonly used as a multistage (8 or 10 stage) pump have been investigated experimentally. Due to the complex three-dimensional geometries, the hydraulic performance of multistage pumps is closely related to the internal flows in diffuser and return vanes. In order to investigate the flow characteristics in these regions by Particle Image Velocimetry (PIV) technique, a transparent pump is designed. A 532 nm continuous laser and a high-speed camera are used as a light source and an image acquisition device, respectively. The velocity field information in a diffuser of the radial pump is successfully obtained by two-dimensional PIV measurements at various operating conditions.

Inter-Blade Vortex Characteristics With the Blockage Effects of Runner Blade in a Francis Hydro Turbine Model

2019 ◽  
Author(s):  
Seung-Jun Kim ◽  
Jin-Hyuk Kim ◽  
Young-Seok Choi ◽  
Yong Cho ◽  
Jong-Woong Choi
Keyword(s):  
Flow Rate ◽  
Flow Characteristics ◽  
Internal Flow ◽  
Operating Conditions ◽  
Low Flow ◽  
Hydro Turbine ◽  
Runner Blade ◽  
Performance Reduction ◽  
Turbine Model ◽  
Low Flow Rate

Abstract This study presents the numerical analysis on the inter-blade vortex characteristics along with the blockage effects of runner blade in a Francis hydro turbine model with various flow rate conditions. The turbine model showed different flow characteristics in the runner blade passages according to operating conditions, and inter-blade vortex was observed at lower flow rate conditions. This inter-blade vortex can lead to performance reduction, vibration, and instability for smooth operation of turbine systems. The previous study on blockage effects on various runner blade thickness, showed its influence on hydraulic performance and internal flow characteristics at low flow rate conditions. Therefore, the inter-blade vortex characteristics can be altered with the blockage effects at low flow rate conditions in a Francis hydro-turbine. For investigating the internal flow and unsteady pressure characteristics, three-dimensional steady and unsteady Reynolds-averaged Navier-Stokes calculations are performed. These inter-blade vortices were captured at the leading and trailing edges close to the runner hub. These vortex regions showed flow separation and stagnation flow while blockage effects contributed for decreasing the inter-blade vortex at low flow rate conditions.

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