Effect of the Cross-Sectional Shape of Recirculation Channel on Expelling Air Bubbles in the FDBs of HDD Spindle Motors

2014 ◽  
Author(s):  
Y. H. Jung ◽  
G. H. Jang ◽  
C. H. Kang ◽  
H. H. Shin ◽  
J. Y. Jeong
Keyword(s):  
Fluid Dynamic ◽  
Hard Disk Drives ◽  
Navier Stokes ◽  
Air Bubbles ◽  
Navier Stokes Equation ◽  
Cross Sectional ◽  
Air Bubble ◽  
Trapped Air ◽  
Large Pressure ◽  
Fast Flow

Fluid dynamic bearings (FDBs) are applied to most of the spindle motors of computer hard disk drives (HDDs) since FDBs provide better dynamic characteristics, such as lower vibration and noise, than ball bearings. However, a weakness of FBDs is instability arising from air bubbles in the oil lubricant of FDBs. One possible solution to expel the trapped air bubbles out of FDBs is to include recirculation channel (RC). RC is designed to balance the pressures between upper and lower parts of FDBs and to circulate the oil lubricant as well as to expel air bubbles out of FDBs. This paper experimentally and numerically investigates the behavior of the air bubble in oil lubricant of operating FDBs due to the design of the RC. We created the FDBs with transparent cover and performed the experiment to visually observe the behavior of trapped air bubbles. Also, we numerically studied the phenomena of expelling the air bubble. The flow field of FDBs is calculated by the Navier-Stokes equation and the continuity equation. And we numerically explained that large pressure difference between upper and lower regions of RC and fast flow velocity along RC expel the air bubble out of FDBs. This research can be effectively utilized to develop robust FDBs by expelling the air bubbles out of FDBs.

A fast multiobjective optimization approach to S-duct scoop inlets design with both inflow and outflow

2018 ◽  
Vol 233 (9) ◽  
pp. 3381-3394
Author(s):  
Lifang Zeng ◽  
Dingyi Pan ◽  
Shangjun Ye ◽  
Xueming Shao
Keyword(s):  
Multiobjective Optimization ◽  
Total Pressure ◽  
Optimization Method ◽  
Navier Stokes ◽  
Integral Model ◽  
Optimization Approach ◽  
Navier Stokes Equation ◽  
Cross Sectional ◽  
Design Variables ◽  
Computational Fluid Dynamics Analysis

A fast multiobjective optimization method for S-duct scoop inlets considering both inflow and outflow is developed and validated. To reduce computation consumption of optimization, a simplified efficient model is proposed, in which only inflow region is simulated. Inlet pressure boundary condition of the efficient model is specified by solving an integral model with both inflow and outflow. An automated optimization system integrating the computational fluid dynamics analysis, nonuniform rational B-spline geometric representation technique, and nondominated sorting genetic algorithm II is developed to minimize the total pressure loss and distortion at the exit of diffuser. Flow field is numerically simulated by solving the Reynolds-averaged Navier–Stokes equation coupled with k–ω shear stress transport turbulence model, and results are validated to agree well with previous experiment. S-duct centreline shape and cross-sectional area distribution are parameterized as the design variables. By analyzing the results of a suggested optimal inlet chosen from the obtained Pareto front, total pressure recovery has increased from 97% to 97.4%, and total pressure distortion DC60 has decreased by 0.0477 (21.7% of the origin) at designed Mach number 0.7. The simplified efficient model has been validated to be reliable, and by which the time cost for the optimization project has been reduced by 70%.

Behavior of Micron-Sized Air Bubble in Operating FDBs by Using the Discrete Phase Modeling Method

2013 ◽  
Author(s):  
Y. H. Jung ◽  
G. H. Jang ◽  
K. M. Jung ◽  
C. H. Kang ◽  
H. H. Shin
Keyword(s):  
Fluid Dynamic ◽  
Disk Drive ◽  
Spindle Motor ◽  
Air Bubbles ◽  
Air Bubble ◽  
Discrete Phase Modeling ◽  
Discrete Phase ◽  
The Stability ◽  
Stiffness And Damping ◽  
Oil Injection

Fluid dynamic bearings (FDBs) have been applied to the spindle motor of a computer hard disk drive (HDD) because FDBs provide better dynamical characteristics of lower vibration and noise than ball bearings. However, one of the weaknesses of FBDs is the instability arising from the air bubble in oil lubricant of FDBs. Air bubbles are formed and trapped in oil lubricant by the inappropriate process of oil injection or the external shock. Trapped air bubbles decrease the rotational accuracy and the stability of a rotor-bearing system in such a way to generate non-repeatable run-out (NRRO) and to decrease the stiffness and damping coefficients of FDBs. It is important to predict the path of air bubbles in oil lubricant and to design FDBs in such a way to easily expel air bubbles out of operating FDBs.

Investigation of the 3D Flow in Hemodialysis Venous Air Traps

2014 ◽  
Vol 553 ◽  
pp. 156-161
Author(s):  
Gholamreza Keshavarzi ◽  
Tracie J. Barber ◽  
Guan Heng Yeoh ◽  
Anne Simmons
Keyword(s):  
Fluid Dynamic ◽  
Waste Product ◽  
The Body ◽  
Flow Structures ◽  
Air Bubbles ◽  
Health Issues ◽  
3D Flow ◽  
Air Bubble ◽  
Different Types ◽  
Flow Phenomena

Hemodialysis is an extracorporeal system which removes the waste product from kidneys for patients with kidney failure. Air bubbles within the system can cause several deficiencies to the system, and more importantly serious health issues to the patients. Therefore, different types of air traps (artery and venous side) are situated in the setup to prevent air bubbles passing through the system and being sent to the body. There have been evidence of the air trap deficiency. In order to understand these deficiencies the flow inside these air traps need to be understood. The investigation of the flow structures in air traps allow us to predict the efficiency of the air traps in capturing the air bubbles and preventing them from passing through. Computational fluid dynamic (CFD) has been used to compare the flow inside both these air traps. The results show interesting flow phenomena leading to explanations of the air bubble capturing effect.

Flow resistance of ice-covered streams

1984 ◽  
Vol 11 (4) ◽  
pp. 815-823 ◽  
Author(s):  
S. P. Chee ◽  
M. R. I. Haggag
Keyword(s):  
Velocity Profile ◽  
Channel Flow ◽  
Flow Resistance ◽  
Ice Cover ◽  
Navier Stokes ◽  
Navier Stokes Equation ◽  
Cross Sectional ◽  
Roughness Elements ◽  
Mixing Length Theory ◽  
Good Agreement

This paper deals with the underlying theory of the hydraulics of channel flow with a buoyant boundary as an ice cover. It commences by developing the velocity distribution in two-dimensional covered channel flow using the Reynolds form of the Navier–Stokes equation in conjunction with the Prandtl – Von Karman mixing length theory. Central to the theory is the division of the channel into two subsections. From the developed velocity profile, the functional relationship for the division surface is obtained. Finally, the composite roughness of the channel is derived.Experimental verification of the developed theory was conducted in laboratory flumes. Seven cross-sectional shapes were utilized. Ice covers were simulated with polyethylene plastic pellets as well as floating plywood boards with roughness elements attached to the underside. Velocity profile and composite roughness measurements made in these flumes were in good agreement with the theoretical equations. The composite roughness relationship derived from the theory is very comprehensive, as it takes into account not only the varying rugosities of the channel and its floating boundary but also the shape of the cross section. Key words: composite roughness, ice cover, flow resistance, velocity profile, buoyant boundary, covered channel.

Computerized Fluid Dynamic Study of Parameter Effects on the Performance of Coaxial Propellers

2020 ◽  
Vol 17 (7) ◽  
pp. 3237-3242
Author(s):  
Young-Tae Kim ◽  
Chang Hwan Park ◽  
Hak Yoon Kim
Keyword(s):  
Pitch Angle ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Navier Stokes Equation ◽  
Steady State Condition ◽  
Performance Variation ◽  
Air Vehicle ◽  
Program Star ◽  
And Control

The computerized fluid dynamic (CFD) analysis was performed for 1.8 m diameter coaxial propellers to be applied to the multi-copter type Personal Air Vehicle (PAV) having conceptually 600 kg of Maximum Take-Off Weight (MTOW). Methods/Statistical analysis: Using the commercial CFD program STAR-CCM+ (13.03.11), the coaxial propellers were analyzed at the same RPM under the steady state condition. The three-dimensional Compressible Reynolds Mean Navier-Stokes equation was applied and the Moving Reference Frame (MRF) technique was used. With the optimum single pitch angle of upper propeller, the lower propeller’s pitch was changed for the varying propeller spacing to identify the performance variation and the interference effect. The lower propeller has to be different pitch setting other than the upper propeller’s optimum pitch angle because of the interfered flow effect between propellers. The propeller spacing is not so sensitive to efficiency if the spacing is more than 0.25 of propeller diameter. Study shows that the identified pitches and spacing of coaxial propellers are essential for designing the configuration and control of multi-copter type PAV which uses variable pitch propellers for safety and efficiency.

Adjoint-Based Design Optimization of S-Shaped Intake Geometry

2017 ◽  
Author(s):  
Rasoul Askari ◽  
Peyman Shoureshi ◽  
Mohammad Reza Soltani ◽  
Afshin Khajeh Fard
Keyword(s):  
Adjoint Method ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Shape Modification ◽  
Optimization Scheme ◽  
Navier Stokes Equation ◽  
Cross Sectional ◽  
Sst Turbulence Model ◽  
Air Intake ◽  
Air Intake Geometry

The S-shaped air intakes are very common shapes due to their ease in the engine-body integration or Radar Cross Section, RCS, specifications especially for fighter aircrafts. The numerical shape optimization of an S-shaped air intake using adjoint method is conducted. The flow of a specified air intake that uses S-duct M2129 is simulated using three dimensional (3D) numerical solution of Reynolds-Averaged Navier-Stokes equation along with k-ω SST turbulence model. The main purpose of this optimization scheme is to maximize the total pressure recovery (TPR). Further, the scheme is developed in such a way that would be applicable in industry thru satisfying specified constraint requirements. The cross sectional areas of the geometry of duct inlet and outlet (known as engine face) remain unchanged. In addition, small shape modification in each optimization step is considered. Finally after nine optimization cycles new S-shaped air intake geometry with higher TPR and lower distortion (DC) is generated, that would achieve higher performance during its operation.

An Analysis for Plane Strain Plastic Deformation in Metal-Working Process

1977 ◽  
Vol 99 (3) ◽  
pp. 727-732 ◽  
Author(s):  
Y. S. Lee ◽  
M. R. Patel
Keyword(s):  
Plane Strain ◽  
Plastic Flow ◽  
Fluid Dynamic ◽  
Constitutive Relations ◽  
Flow Equation ◽  
Navier Stokes ◽  
Navier Stokes Equation ◽  
Rate Behavior ◽  
Strain Equation ◽  
Strain Rate Behavior

The two-dimensional plane strain equation of large plastic flow, expressed in terms of the stream function gradients, is modified using complex variables. The resulting governing equation is solved analytically for a class of nonlinear materials whose stress-strain rate behavior can be expressed by σ¯ = ce¯˙m. A one-to-one correspondence between the plastic flow equation using the Levy-Mises constitutive relations and the Navier-Stokes equation of fluid flow with zero inertia term is established for constant λ˙. This correspondence allows the existing fluid dynamic solution to be used for the plasticity analysis. An analytical solution of plane strain extrusion of linear material through square-cornered die is presented to illustrate the procedure.

Computational Prediction of Hemolysis by Blade Flow Field of Micro-Axial Blood Pump

2006 ◽  
Author(s):  
Xin Chen ◽  
Jianping Tan
Keyword(s):  
Blood Flow ◽  
Flow Field ◽  
Fluid Dynamic ◽  
Computational Prediction ◽  
Blood Pump ◽  
Navier Stokes ◽  
Initial Attempt ◽  
Navier Stokes Equation ◽  
Blood Damage ◽  
Blood Pumps

By analyzing fluid dynamics of blood in an artificial blood pump and simulating the flow field structure and the flow performance of blood, the blood flow and the damages in the designed blood pump would be better understood. This paper describes computational fluid dynamic (CFD) used in predicting numerically the hemolysis of blade in micro-axial blood pumps. A numerical hydrodynamical model, based on the Navier-Stokes equation, was used to obtain the flow in a micro-axial blood pump. A time-dependent stress acting on blood particle is solved in this paper to explore the blood flow and damages in the micro-axial blood pump. An initial attempt is also made to predict the blood damage from these simulations.

The advance ratio effect on the lift augmentations of an insect-like flapping wing in forward flight

2016 ◽  
Vol 808 ◽  
pp. 485-510 ◽  
Author(s):  
Jong-Seob Han ◽  
Jo Won Chang ◽  
Jae-Hung Han
Keyword(s):  
Leading Edge ◽  
Flapping Wing ◽  
Navier Stokes ◽  
Navier Stokes Equation ◽  
Cross Sectional ◽  
Image Velocimetry ◽  
Force Moment ◽  
Edge Vortex ◽  
Advance Ratio ◽  
High Reynolds

Time-varying force/moment measurements and digital particle image velocimetry (DPIV) were conducted to reveal the influence of an advance ratio $J$ on an insect-like flapping wing. A scaled-up robotic model and a servo-driven towing tank were employed to investigate nine individual $J$ cases – $J=0$ (hovering), 0.0625, 0.1250, 0.1875, 0.25, 0.50, 0.75, 1.0 and $\infty$ (gliding motion) – at a high Reynolds number ($Re\sim 10^{4}$). At $J\leqslant 0.25$, the aerodynamic forces slightly increased from those in hover ($J=0$). The centres of pressure in these cases were concentrated in the outboard section, and the leading-edge vortices (LEVs) grew more conically than those in hover. Spanwise cross-sectional DPIV indicated that the wings generated more balanced downwashes, which effectively supported the slight lift increments in this range. At $J>0.25$, a drastic force drop appeared as $J$ increased. The DPIV results in the $J=0.5$ case clearly showed a strong trailing-edge vortex on the outboard trailing edges encroaching into the upper surface, which had been occupied by the LEV for lower $J$. The LEV vorticity was noticeably weakened, and coherent substructures with substantial turbulence accompanied this vorticity. In the $J=1.0$ case, such encroachment was extended to 50 % of the section, and the LEV outboard became significantly irregular. The near-wake structures also showed that the $J=1.0$ case had the narrowest downwash area, with unstable root and tip vortices, which reflected considerable attenuation in the lift enhancements. It was of note that all of these vortical behaviours were clearly distinguishable from aspect ratio ($AR$) effects. The $J$ even played a similar role to that of the $AR$ in the Navier–Stokes equation. These findings clearly indicated that the $J$ could be an independent quantity governing the overall vortical system and lift enhancing mechanism on a flapping wing of a flapping-wing micro air vehicle.

Effect of dome size on flow dynamics in saccular aneurysms – A numerical study

2020 ◽  
Vol 14 (3) ◽  
pp. 7181-7190
Author(s):  
Sathvik Nayak H. S. ◽  
Nitesh Kumar ◽  
S. M. A. Khader ◽  
Raghuvir Pai
Keyword(s):  
Numerical Study ◽  
Fluid Dynamic ◽  
Flow Dynamics ◽  
Arterial System ◽  
Navier Stokes ◽  
Hemodynamic Parameters ◽  
Navier Stokes Equation ◽  
Neck Size ◽  
Human Arteries ◽  
Velocity Pressure

Image-based Computational Fluid Dynamic (CFD) simulations of anatomical models of human arteries are gaining clinical relevance in present days. In this study, CFD is used to study flow behaviour and hemodynamic parameters in aneurysms, with a focus on the effect of geometric variations in the aneurysm models on the flow dynamics. A computational phantom was created using a 3D modelling software to mimic a spherical aneurysm. Hemodynamic parameters were obtained and compared with the available literature to validate. Further, flow dynamics is studied by varying the dome size of the aneurysm from 3.75 mm to 6.25 mm with an increment of 0.625 mm keeping the neck size constant. The aneurysm is assumed to be located at a bend in the arterial system. Computational analysis of the flow field is performed by using Navier – Stokes equation for laminar flow of incompressible, Newtonian fluid. Parameters such as velocity, pressure, wall shear stress (WSS), vortex structure are studied. It was observed that the location of the flow separation and WSS vary significantly with the geometry of the aneurysm. The reduction of WSS inside the aneurysm is higher at the larger dome sizes for constant neck size.

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