Granular flow induced by high-speed in-plane impact on particle sheet and its fluid dynamic description

2019 ◽  
Author(s):  
Kojiro Suzuki
Keyword(s):  
Granular Flow ◽  
High Speed ◽  
Fluid Dynamic ◽  
Dynamic Description

Thermo-Fluid-Dynamic Design of Reciprocating Compressor Cylinders by Fluid Structure Interaction (FSI)

2011 ◽  
Author(s):  
Riccardo Traversari ◽  
Alessandro Rossi ◽  
Marco Faretra
Keyword(s):  
High Speed ◽  
Fluid Dynamic ◽  
Fluid Structure Interaction ◽  
Classical Equation ◽  
Flow Coefficient ◽  
Reciprocating Compressor ◽  
Complex Situation ◽  
Fluid Structure ◽  
Associated Gas ◽  
Structure Interaction

Pressure losses at the cylinder valves of reciprocating compressors are generally calculated by the classical equation of the flow through an orifice, with flow coefficient determined in steady conditions. Rotational speed has increased in the last decade to reduce compressor physical dimensions, weight and cost. Cylinder valves and associated gas passages became then more and more critical, as they determine specific consumption and throughput. An advanced approach, based on the new Fluid Structure Interaction (FSI) software, which allows to deal simultaneously with thermodynamic, motion and deformation phenomena, was utilized to simulate the complex situation that occurs in a reciprocating compressor cylinder during the motion of the piston. In particular, the pressure loss through valves, ducts and manifolds was investigated. A 3D CFD Model, simulating a cylinder with suction and discharge valves, was developed and experimentally validated. The analysis was performed in transient and turbulent condition, with compressible fluid, utilizing a deformable mesh. The 3D domain simulating the compression chamber was considered variable with the law of motion of the piston and the valve rings mobile according to the fluid dynamic forces acting on them. This procedure is particularly useful for an accurate valve loss evaluation in case of high speed compressors and heavy gases. Also very high pressure cylinders, including LDPE applications, where the ducts are very small and MW close to the water one, can benefit from the new method.

scholarly journals A schlieren optical study of the human cough with and without wearing masks for aerosol infection control

2009 ◽  
Vol 6 (suppl_6) ◽  
Author(s):  
Julian W. Tang ◽  
Thomas J. Liebner ◽  
Brent A. Craven ◽  
Gary S. Settles
Keyword(s):  
High Speed ◽  
Fluid Dynamic ◽  
Human Subjects ◽  
Tracer Gas ◽  
Airborne Infection ◽  
Dynamic Mechanisms ◽  
Human Volunteers ◽  
Natural Mechanism ◽  
Time Changes ◽  
Aerosol Infection

Various infectious agents are known to be transmitted naturally via respiratory aerosols produced by infected patients. Such aerosols may be produced during normal activities by breathing, talking, coughing and sneezing. The schlieren optical method, previously applied mostly in engineering and physics, can be effectively used here to visualize airflows around human subjects in such indoor situations, non-intrusively and without the need for either tracer gas or airborne particles. It accomplishes this by rendering visible the optical phase gradients owing to real-time changes in air temperature. In this study, schlieren video records are obtained of human volunteers coughing with and without wearing standard surgical and N95 masks. The object is to characterize the exhaled airflows and evaluate the effect of these commonly used masks on the fluid-dynamic mechanisms that spread infection by coughing. Further, a high-speed schlieren video of a single cough is analysed by a computerized method of tracking individual turbulent eddies, demonstrating the non-intrusive velocimetry of the expelled airflow. Results show that human coughing projects a rapid turbulent jet into the surrounding air, but that wearing a surgical or N95 mask thwarts this natural mechanism of transmitting airborne infection, either by blocking the formation of the jet (N95 mask), or by redirecting it in a less harmful direction (surgical mask).

Three-Dimensional CFD Analysis of Meshing Losses in a Spur Gear Pair

2018 ◽  
Author(s):  
T. Fondelli ◽  
D. Massini ◽  
A. Andreini ◽  
B. Facchini ◽  
F. Leonardi
Keyword(s):  
High Speed ◽  
Numerical Study ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Spur Gear ◽  
Computational Domain ◽  
Gear Pair ◽  
Transient Pressure ◽  
Numerical Effort ◽  
Free Environment

The reduction of fluid-dynamic losses in high speed gearing systems is nowadays increasing importance in the design of innovative aircraft propulsion systems, which are particularly focused on improving the propulsive efficiency. Main sources of fluid-dynamic losses in high speed gearing systems are windage losses, inertial losses resulting by impinging oil jets used for jet lubrication and the losses related to the compression and the subsequent expansion of the fluid trapped between gears teeth. The numerical study of the latter is particularly challenging since it faces high speed multiphase flows interacting with moving surfaces, but it paramount for improving knowledge of the fluid behavior in such regions. The current work aims to analyze trapping losses in a gear pair by means of three-dimensional CFD simulations. In order to reduce the numerical effort, an approach for restricting computational domain was defined, thus only a portion of the gear pair geometry was discretized. Transient calculations of a gear pair rotating in an oil-free environment were performed, in the context of conventional eddy viscosity models. Results were compared with experimental data from the open literature in terms of transient pressure within a tooth space, achieving a good agreement. Finally, a strategy for meshing losses calculation was developed and results as a function of rotational speed were discussed.

The Granular Lubricated Journal Bearing: Evidence of Lift Formation

2019 ◽  
Vol 141 (4) ◽  
Author(s):  
Venkata K. Jasti ◽  
Martin C. Marinack ◽  
Deepak Patil ◽  
C. Fred Higgs
Keyword(s):  
Carrying Capacity ◽  
Granular Flow ◽  
High Speed ◽  
Journal Bearing ◽  
Hydrodynamic Lubrication ◽  
Flow Behavior ◽  
Extreme Environments ◽  
Granular Flows ◽  
Load Carrying Capacity ◽  
Load Carrying

This work demonstrates that granular flows (i.e., macroscale, noncohesive spheres) entrained into an eccentrically converging gap can indeed actually exhibit lubrication behavior as prior models postulated. The physics of hydrodynamic lubrication is quite well understood and liquid lubricants perform well for conventional applications. Unfortunately, in certain cases such as high-speed and high-temperature environments, liquid lubricants break down making it impossible to establish a stable liquid film. Therefore, it has been previously proposed that granular media in sliding convergent interfaces can generate load carrying capacity, and thus, granular flow lubrication. It is a possible alternative lubrication mechanism that researchers have been exploring for extreme environments, or wheel-regolith traction, or for elucidating the spreadability of additive manufacturing materials. While the load carrying capacity of granular flows has been previously demonstrated, this work attempts to more directly uncover the hydrodynamic-like granular flow behavior in an experimental journal bearing configuration. An enlarged granular lubricated journal bearing (GLJB) setup has been developed and demonstrated. The setup was made transparent in order to visualize and video capture the granular collision activity at high resolution. In addition, a computational image processing program has been developed to process the resulting images and to noninvasively track the “lift” generated by granular flow during the journal bearing operation. The results of the lift caused by granular flow as a function of journal rotation rate are presented as well.

A CFD Study on the Dynamic Coefficients of Labyrinth Seals

2012 ◽  
Author(s):  
Donghui Zhang ◽  
Chester Lee ◽  
Michael Cave
Keyword(s):  
High Speed ◽  
Fluid Dynamic ◽  
Labyrinth Seal ◽  
Leakage Flow ◽  
Labyrinth Seals ◽  
Dynamic Coefficients ◽  
Rotating Impeller ◽  
Coupling Stiffness ◽  
Direct Stiffness ◽  
Compressor Efficiency

Labyrinth seals are widely used in gas compressors to reduce internal leakage and increase the compressor efficiency. Due to the eccentricity between the rotating impeller and the stationary part as *well as the shaft whirling motion, forces are generated when the leakage flow passing through the cavities and the seals. For a lot of applications with high speed and pressure, these forces can drive the system unstable. Thus, predicting the forces accurately become a very important for compressor rotordynamic designs. A lot of research and studies has been done to the seals itself, including bulk flow method, computational fluid dynamic (CFD) and test measurement. The seal and leakage flow interaction forces can be predicted relatively accurate. But very few research treat the seal and cavities as one component interacting with the leakage flow and produce the forces. This paper presents results of CFD investigations on the dynamic coefficients of one typical impeller eye seal and front cavity. The CFD results show that large forces are generated in the front cavity due to circumferential uniform pressure distribution, which caused by the downstream labyrinth seal. The forces generated in the front cavity are more than in the front seal. It was found that the inertia, damping, and stiffness are proportional to average pressure. The cross-coupling stiffness increases with speed with power of 2 while the direct stiffness increases with speed with power of about 1.7.

The Coefficient of Restitution of Spheroid Particles Impacting on a Wall—Part I: Experiments

2018 ◽  
Vol 85 (4) ◽  
Author(s):  
Ming Hu ◽  
Yrjö Jun Huang ◽  
Fei Wang ◽  
Martin Smedstad Foss
Keyword(s):  
Inclination Angle ◽  
Granular Flow ◽  
High Speed ◽  
Contact Point ◽  
Prolate Spheroid ◽  
Spherical Particles ◽  
Dimensionless Number ◽  
Discrete Element Modeling ◽  
The Relationship ◽  
Spheroid Particle

Coefficients of restitution (CoR) is used to scale the kinetic energy dissipation, which is a necessary parameter for discrete element modeling simulations of granular flow. Differences from the collision of spherical particles, CoRs of spheroid particle are affected not only by materials, particle size, and impacting velocity, but also by the contact inclination angle of the particle. This article presents our experimental investigation to measure the velocities of translation and rotation using high-speed camera and calculate the CoR in normal direction of prolate spheroid particles impacting flat targets. The results show that this CoR of a prolate spheroid particle is composed of two parts, translation and rotation. The effect from the contact inclination angle is not obvious for a given velocity. When the contact point is close to a pole, the first part plays a major role. On the contrary, the second part dominates the CoR, when the contact point is close to the equator. A dimensionless number, e*, is defined to scale the proportion of velocity due to rotation in the total rebound velocity at the contact point. The relationship between the contact inclination angle, ϕ, and e* for 25 deg < ϕ < 90 deg is given in this article.

CFD Modelling of Loss of Vacuum Accident (LOVA) for CFETR

2018 ◽  
Author(s):  
Youyou Xu ◽  
Songlin Liu ◽  
Xiaoman Cheng ◽  
Xuebin Ma
Keyword(s):  
High Speed ◽  
Reverse Flow ◽  
Fluid Dynamic ◽  
Fusion Energy ◽  
Normal Operation ◽  
Vacuum Vessel ◽  
Cfd Modelling ◽  
Ansys Cfx ◽  
Section Area ◽  
Break Area

Chinese Fusion Engineering Testing Reactor (CFETR) is a tokamak-type machine and next device in the roadmap for the realization of fusion energy in China, which aims to bridge the gaps between the International Thermonuclear Experimental Reactor (ITER) and the demonstration reactor (DEMO) [1]. The accident sequence starting from loss of vacuum accident (LOVA) is an important issue concerning the performance of CFETR. During LOVA, air will leak into the vacuum vessel (VV) causing fast pressurization of VV. At the same time, the high speed airflow jet will result in migration and re-suspension of the large quantity of tungsten dust produced and deposited in the lower part of plasma chamber, causing possibilities of radioactive dust leakage into the workshop and environment. In order to conduct a comprehensive analysis of the accident sequence, firstly, the airflow characteristics of LOVA should be studied. In this article, a postulated rupture of different section area is assumed due to a failed component at the equatorial port level. The computational fluid dynamic (CFD) modelling of LOVA was conducted by ANSYS CFX. The results show that the break area has significant influences on the characteristics of the airflow. Two swirling airflows are formed in the upper and lower part of the torus. The airflow characteristics are quite different when the LOVA happens during maintenance or during normal operation. A reverse flow occurs when the LOVA happens during normal operation. Yet can not be observed when LOVA occurs during maintenance. The results are the basis to the further safety study of CFETR such as the re-suspension, migration and explosion of dust.

Explicit Finite Element Simulation of Granular Flow in an Annular Shear Cell

2009 ◽  
Author(s):  
M. A. Kabir ◽  
C. F. Higgs ◽  
M. R. Lovell ◽  
V. Jasti ◽  
M. C. Marinack
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Granular Flow ◽  
High Speed ◽  
Flow Behavior ◽  
Shear Cell ◽  
Explicit Finite Element Method ◽  
Explicit Finite Element ◽  
Annular Shear Cell ◽  
Element Method

Explicit finite element method modeling of granular flow behavior in an annular shear cell has been studied and presented in this paper. The explicit finite element method (FEM) simulations of granular flow in an annular shear cell with around 1633 particles were performed, where the inner wheel rotated at a very high speed and the outer disk remained stationary. The material properties of the particles and the outer wheel were defined as elastic steel whereas the inner wheel was elastic aluminum. In this investigation, the explicit FEM model mimicked granular flow in an experimental set up where the inner wheel was rotated at a speed of 240 rpm. The FEM results for shearing motion and solid fraction were compared with experimental results from a granular shear cell.

scholarly journals Numerical Optimization of a Stall Margin Enhancing Recirculation Channel for an Axial Compressor

Fluids ◽  
2019 ◽  
Vol 4 (2) ◽  
pp. 88
Author(s):  
Motoyuki Kawase ◽  
Aldo Rona
Keyword(s):  
High Speed ◽  
High Performance ◽  
Fluid Dynamic ◽  
Axial Compressor ◽  
Leading Edge ◽  
Navier Stokes ◽  
Test Case ◽  
Dynamic Simulations ◽  
Stall Margin ◽  
Casing Treatment

A proof of concept is provided by computational fluid dynamic simulations of a new recirculating type casing treatment. This treatment aims at extending the stable operating range of highly loaded axial compressors, so to improve the safety of sorties of high-speed, high-performance aircraft powered by high specific thrust engines. This casing treatment, featuring an axisymmetric recirculation channel, is evaluated on the NASA rotor 37 test case by steady and unsteady Reynolds Averaged Navier Stokes (RANS) simulations, using the realizable k-ε model. Flow blockage at the recirculation channel outlet was mitigated by chamfering the exit of the recirculation channel inner wall. The channel axial location from the rotor blade tip leading edge was optimized parametrically over the range −4.6% to 47.6% of the rotor tip axial chord c z . Locating the channel at 18.2% c z provided the best stall margin gain of approximately 5.5% compared to the untreated rotor. No rotor adiabatic efficiency was lost by the application of this casing treatment. The investigation into the flow structure with the recirculating channel gave a good insight into how the new casing treatment generates this benefit. The combination of stall margin gain at no rotor adiabatic efficiency loss makes this design attractive for applications to high-speed gas turbine engines.

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