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In this paper, the effects of two flow-induced vibration (FIV) mitigation components on hard disk drive (HDD) airflow, vortex splitters and flow diverters, were verified. The edges of the components were also modified by filleting and the resulting effect on airflow determined. A perspective review on HDDs and their operation, and the mechanism and...
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... Hard Disk Drive (HDD, Fig. 1) is an essential part of our world today. The incredible ability of a HDD to store and preserve large amounts of data together with a fast rate of data recording and retrieving has made it the dominant device for data storage in computers. With the development of technology, the demand for intensive storage space and the read/write ...
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... study verified the effectiveness and result of airflow simulation in a HDD using the RANS RNG k-model and the LES model in FLUENT. A commercially available full 3.5 inch HDD model was used (Figs. 9, 10). A disk angular velocity of 500 rad/s, giving a Reynolds number of 12.5 x 10 4 , which exceeds the critical Re value of 2x10 4 for rotating disk [26]. The RNG k-model was run for 10000 iterations. The LES model used was the Sub-Grid Dynamic Smargorinsky-Lilly Model. A time-step of 2 x 10e -6 s was applied and the model was run for ...
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... the converged RNG k-model solution was perturbed to produce the initial velocity condition for the start of the LES. Then, the LES Model was run. This method creates a much more realistic initial field for the LES run. It reduces the time needed for the LES to reach a statistically stable mode and decreases the tendency of non-convergence [25]. Figs. (11, 12) show the tangential velocity and static pressure contour plots from the models at the defined horizontal plane of z=9.665mm. Results indicated much more smoothened out flow contours in the RNG k-model as compared to the LES model. The numerical values obtained from both models were in the same order and range. The RNG k-model gave ...
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... A consists of the full original 3.5 inch HDD with Vortex Splitters (Figs. 9, 13), Model B is a full original 3.5 inch HDD with Splitter and Diverters (Figs. 14, 15), while Model C is also a full original 3.5 inch HDD consisting the Modified Splitters and Diverters (Figs. 16, 17). The hypothesis taken was that Model C would be more effective than Model B in terms of reducing the simulated values such as turbulent ...
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... A consists of the full original 3.5 inch HDD with Vortex Splitters (Figs. 9, 13), Model B is a full original 3.5 inch HDD with Splitter and Diverters (Figs. 14, 15), while Model C is also a full original 3.5 inch HDD consisting the Modified Splitters and Diverters (Figs. 16, 17). The hypothesis taken was that Model C would be more effective than Model B in terms of reducing the simulated values such as turbulent intensity and z-Velocity values in HDD airflow. The splitters and diverters in Model C ...
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... A consists of the full original 3.5 inch HDD with Vortex Splitters (Figs. 9, 13), Model B is a full original 3.5 inch HDD with Splitter and Diverters (Figs. 14, 15), while Model C is also a full original 3.5 inch HDD consisting the Modified Splitters and Diverters (Figs. 16, 17). The hypothesis taken was that Model C would be more effective than Model B in terms of reducing the simulated values such as turbulent intensity and z-Velocity values in HDD airflow. The splitters and diverters in Model C had filleted edges which intend to make them more aerodynamic streamlining towards airflow. ...
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... Diverters: Similarly to the vortex splitters, the straight edges of the flow diverters were filleted to remove all sharp contours and created rounder leading edges. The fillet width and angle was identical for all edges. All diverter edges were filleted. Fig. (14). Skeletal view of HDD Model B with top cover removed (added with ...
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... percentage changes were computed based on taking Model A as base reference. Model B had a 0.17% increase in tangential velocity (m/s) while Model C had a 1.37% decrease (Fig. 18). Models B and C had substantial reduction in the z-Velocity (m/s) values of 26.2% and 27% respectively. Both models also indicated a decrease in local maximum Turbulent Intensity (%), with a 8.55% decrease for Model B and a 7.11% in Model C (Fig. 19). Both Models B and C indicated a total increase in about 4% in total moment, which ...
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... Model B had a 0.17% increase in tangential velocity (m/s) while Model C had a 1.37% decrease (Fig. 18). Models B and C had substantial reduction in the z-Velocity (m/s) values of 26.2% and 27% respectively. Both models also indicated a decrease in local maximum Turbulent Intensity (%), with a 8.55% decrease for Model B and a 7.11% in Model C (Fig. 19). Both Models B and C indicated a total increase in about 4% in total moment, which translates to the total power used to operate the HDD ( Table 2). The indicated increases in power are however still within an acceptable figure in HDD operation (i.e. below ...
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... splitters, it may however prove challenging to manufacture such small filleted components for HDD production. More studies for different disk rotation speeds (i.e. different Reynolds number), but maintaining turbulent airflow conditions are needed to establish the relationship of the FIV device effect on airflow and the flow Reynolds number. Fig. (19). Turbulent intensity contours of Models A (top), B (middle) and C (bottom). Circles indicate area of change from previous model. ...
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Numerical simulations are studied for a circular cylinder undergoing Flow-Induced Vibration (FIV) in highly turbulent cross-flow. The study focuses on wake turbulence and its interaction with the structural response being set in a single degree of Freedom. A novel contribution is presented, where a Reynolds number of 140,000 is numerically studied...
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... With the disk rotating at 5400 RPM, the transition Reynolds number of the disk with a 65 mm diameter in the 2.5 inch drive is 80,152 for the air and 6548 for the helium, respectively. Since the transition Reynolds number from the laminar flow to turbulent flow is 2 × 10 4 (Ng et al. 2011), the flow inside the air-filled drive is turbulent, and that is laminar inside the helium-filled drive in this work. Figure 4 shows the temperature gradient contour inside air-and helium-filled drives. ...
The presence of particles, which can intrude into the gas bearing, is one of the most common factors in the failure of hard disk drives (HDDs). Previous works investigated particle trajectories inside air-filled drives without considering temperature effects on the distribution of particles. Actually, especially for the submicron particle, particle trajectories and trapping status are affected by the temperature gradient since the thermophoretic force cannot be ignored. In this paper, considering major heat generation components such as the spindle motor and voice coil motor (VCM), trajectories and trapping status for Al2O3 particles inside a 2.5 inch helium-filled drive are simulated by the commercial computational fluid dynamics solver FLUENT with user-defined functions (UDFs). The trapping criterion for Al2O3 particles is used as boundary conditions for different colliding surfaces. The results reveal that particles in the air-filled drive will more likely degrade the head–disk interface (HDI) reliability. In addition, after considering the temperature, the particle trapping rate by the disk decreases both inside the air-filled drive and the helium-filled drive. And its reduction inside the air-filled drive is larger. Moreover, small particles will more likely degrade the HDI reliability since they can follow the rotatory flow well and have more chance to collide with the disk surface, and then easily attach onto the disk surface.
... With the disk rotating at 5400 RPM, the transition Reynolds number of the disk with a 65 mm diameter in the 2.5 inch drive is 80,152 for the air and 6548 for the helium, respectively. Since the transition Reynolds number from the laminar flow to turbulent flow is 2 × 10 4 (Ng et al. 2011), the flow inside the air-filled drive is turbulent, and that is laminar inside the helium-filled drive in this work. Figure 4 shows the temperature gradient contour inside air-and helium-filled drives. ...
The presence of particles, which can intrude into the air bearing, is one of the most common factors in the failure of hard disk drives (HDDs). Previous works investigated the particle trajectory inside air-filled drives without considering the temperature effects on the distribution of particles. Actually, for the submicron particle, particle trajectory and trapping status are affected by the temperature gradient since the thermophoretic force cannot be ignored. In this paper, considering the major heat generation components such as spindle motor and voice coil motor (VCM), the trajectories and trapping status for Al2O3 particles with diameter of 0.3 μm inside a 2.5 inch helium-filled drive are simulated by the commercial computational fluid dynamics solver FLUENT with user-defined functions (UDFs). The trapping criterion for Al2O3 particles are used as the boundary conditions for the different colliding surfaces.
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... In order to enhancing the reliability and stability of drives, it is very important to understand the flow-induced vibrations and shock-induced vibrations of the HGA. Many works have been carried out to investigate the flow-induced vibrations inside the air-filled drives123456789, including mechanism analysis, structure optimization, and fluid structure interaction studies of the HGA vibrations. Moreover, Aruga et al. [10] compared the positioning accuracy of helium-filled and air-filled drives. ...
... With the disk rotating at 10000 rpm, the transition Reynolds number of disk with 65 mm diameter in the 2.5 inch drive is 80152 for air and 6548 for helium respectively. Since the transition Reynolds number from laminar to turbulent is 2×10 4 [6], the flow inside the air-filled drive is turbulent, and that of helium is laminar in this work. The flow simulations are set up as shown in This article has been accepted for publication in a future issue of this journal, but has not been fully edited. ...
The reliability and stability of hard disk drives (HDDs) are especially important as the areal recording density is rapidly increasing and target to 10 Tb/in2 in the future. The vibrations of the head gimbals assembly (HGA) are inevitable by internal fluid flow and external shock impulses. In this paper, a 3-D finite-element model of an HDD is developed. The internal flow-induced HGA vibrations are investigated by a fluid-structure interaction approach. The external shock-induced vibrations of HGA are also analyzed. The investigated filling gases in the HDD include air and helium.
... With the disk rotating at 5400 RPM, the transition Reynolds number of the disk with a 65 mm diameter in the 2.5 inch drive is 80,152 for the air and 6548 for the helium, respectively. Since the transition Reynolds number from the laminar flow to turbulent flow is 2 × 10 4 (Ng et al. 2011), the flow inside the air-filled drive is turbulent, and that is laminar inside the helium-filled drive in this work. Figure 4 shows the temperature gradient contour inside air-and helium-filled drives. ...
In order to increase the areal recording density of hard disk drive beyond 1 Tb/in2, the flying height has to be reduced to several nanometers. At such a low flying height, particles and lube contaminations, which could lead to a transient vibration and flying height modulation in a hard disk drive, are becoming more and more serious. In this work, it studies the influence of temperature and humidity on the air flow pattern, velocity and shear stress distribution on the air bearing surface (ABS) of slider using a self-developed simulator. It first solves the generalized steady state Reynolds equation with slip boundary conditions. Then it solves the reduced Navier-Stokes (N-S) equation with slip boundary conditions to get the air velocity distribution, i.e., identify the air flow pattern on the ABS. The stagnation lines and areas of air flow are calculated to judge the contamination area. On the other hand, it calculates the air shear stress distribution on the ABS since the air shear stress is the main driving force for the lubricant and particles migration and contaminations. After that, the impact of the temperature and humidity on the air flow pattern is analyzed by applying the Sutherland equation and mixed gas viscosity calculation equation.
The simulation results indicate that the impact of temperature and humidity on the air flow pattern is un-conspicuous. However, the peak velocity of the air flow, which contains no vapor, reduces almost 10%, and the peak air flow shear stress increases less than 1.5%, with the increase of operational temperature from 298.15 K to 343.15 K. In addition, the peak velocity of the air flow increasing almost 4%, and the peak air flow shear stress keeps almost same, with the increase of the operational mole fraction of vapor from 5% to 15%.
We have investigated the stability of a double vortex street, induced in a rectangular container by a tape, or a rope, moving at high speed on its free surface. Depending on the tape velocity and on the geometrical aspect ratios, three patterns of flows are observed: 1) a vortex street with recirculation of the liquid along the lateral sides of the container, 2) the same recirculation but with no stable vortex array, 3) recirculation along the bottom of the container. We have investigated the spatial structure of the vortex street and found that this system explores the phase space available inside a stability tongue predicted at the end of the 1920s by Rosenhead for point vortices in a perfect fluid. Although this very surprising result contrasts with the well-known von Kármán unique stability condition for point vortex streets in an infinite domain, this complements the theory inside a channel of finite breadth. In this paper, we present the very first experimental confirmation of this 90-year-old theory.
Turbulent drag reduction has an important significance for energy conservation and emission reduction of the engineering fields, such as mechanical transmission and longdistance transport pipeline transportation. The air-oil two-phase flow model of non-smooth surfaces of rotating-stationary disk system was established based on the finite volume method, the volume of fluid method and RNG k-e turbulence model. The flow field distribution of lubricant oil is obtained through the numerical analysis of three-dimensional Navier-Stokes equations of the two-phase of lubricating medium inside the rotating-stationary disk system. The turbulent boundary layer flow and stickiness resistance of the rotating-stationary disk system, as well as, the turbulent drag reduction capability by numerical calculation is investigated. The flow field of the smooth surfaces and non-smooth surfaces of rotating-stationary disk system are analyzed and the mechanism of turbulent drag reduction is discussed. The factors of influencing turbulent drag reduction are discussed by changing groove numbers, depth, and area ratio of grooves. The results indicate the grooves make it easier for air to enter the rotating disk system, and the film more easily broken, thus inhibiting the rise in the turbulent drag torque; the turbulent drag reduction efficiency will enhance with the number of grooves increase; will enhance with the depth of grooves increase and will enhance with the area ratio of grooves increase. The results can be used for the flow field analysis and optimization of the rotating-stationary disk system, especially supply a new method to the energy conservation and emission reduction.
The reliability and stability of hard disk drives (HDDs) is especially important as the areal recording density increasing rapidly target to 10 Tb/in2 in the future. The vibration of the Head Gimbals Assembly (HGA) is inevitable by internal fluid flow during operational process. In order to improve this undesirable problem, an acoustic piezoelectric transducer (PZT) actuator which can be used to transform an electric current to an acoustic pressure field, is glued on the HDD cover inner surface to generate acoustic pressure to suppress the flow-induced off-plate vibration (FIOPV) of the HGA. In this paper, a three-dimensional finite element model of HDD is built with an acoustic PZT actuator. The FIOPV of the HGA in the air and helium-filled drives are investigated by fluid–structure interaction simulation method. The acoustic pressure induced vibration (APIV) of the HGA is analyzed by acoustics-piezoelectric-structure interaction simulation method. After that, the suppressed FIOPV after superposing the APIV and the FIOPV is obtained by following the superposition principle.
Abstract The flow field of an open grooved two-disc system was studied. The system includes a rotating finite disc and a stationary finite disc. The rotating disc has radial grooves. The numerical results for the air-oil two-phase flow inside the open grooved two-disc system calculated by the CFD code FLUENT were proposed. The results are discussed and compared with the published test results. The results indicate that the groove affects the transitional characteristics from a single-phase flow to an air-oil two-phase flow of the flow field. In the same flow area, the radial oil flow coefficient is enhanced with a larger groove number. The oil mainly discharges through the groove and the air flows into the non-grooved area from the upstream side of the groove. The effects of the angular velocity on the oil volume fraction and the drag torque become greater when the disc is grooved. It is weakened in the high-velocity operations. The drag torque can be reduced by increasing the groove number in the same flow area. The axial force applied on the disc is gradually decreased with the increase of the angular velocity and becomes close to zero finally. The increase of the groove number reduces the maximum axial force. The results can be used for the optimisation of the Tesla pump and wet clutch.
In industrial hard disk drive research and development laboratories, an environmental chamber is normally used to perform a mechanical verification test of Head Gimbal Assembly (HGA). It is very important to verify that the airflow pattern in the chamber is comparable to that in a real hard disk drive. Hence, we applied a transition shear stress transportation turbulence model (transition SST), one of the robust mathematical models in computer fluid dynamics, to simulate the airflow behavior inside both an environmental chamber and a hard disk drive (HDD). We found that, overall, the two patterns of airflow were not comparable at all. The air velocity vectors around the HGA in VENA were smaller than that in HDD. The reason for this is likely to be that there was more space between the top cover of the chamber and the platter than the space between the top cover of the hard disk drive and its platter.
