Hayato Shimizu

Study of aerodynamic characteristics in hard disk drives by numerical simulation

The behavior of the air flow inside a hard disk drive is evaluated by a three-dimensional unsteady-flow analysis technique called large eddy simulation (LES). The simulation shows that the fluctuation of the aerodynamic force is strongly correlated with the amplitude of the disk vibration, which causes positioning error of the read/write head. It also shows that the power loss caused by the friction of the air on the disks, which accounts for most of the power consumption of hard disk drives at a high-speed revolution, can be qualitatively predicted.

Numerical simulation of positioning error caused by air-flow-induced vibration of head gimbals assembly in hard disk drive

Unsteady airflow in an actual hard disk drive (HDD) which has a rotary actuator is numerically simulated by using LES (large eddy simulation) technique, and the aerodynamic force affecting head gimbals assembly (HGA) is estimated from the simulation. Then calculated force is fed to a structure analysis to predict the airflow-induced vibration of HGA. Lastly, we calculate the head positioning error or the head displacements for the different HGA orientations to explain and classify the mechanism of airflow-induced positioning error (i.e. windage) in HDD.

Large Eddy Simulation of Internal Flow of a Mixed-Flow Pump

Large eddy simulation (LES) of internal flows of a mixed-flow pump is performed. The pump has 5 open impeller blades and twelve diffuser vanes. The objective of the present research is to verify the accuracy of the pump performance prediction by LES with a particular emphasis placed on the instability characteristics. The following two cases of computations are preformed for LES with different grid resolutions. In the first case, we perform LES of internal flow of the pump for a wide range of flow rate, including a flow rate from the shutoff point to the maximum flow. Secondly, we focus on internal flows at flow rates of 55%∼60%, where the instability characteristics take place, with finer computational grid compared to the first case. We use 8 million girds for the first case (the coarse LES), and 78 million girds for the second case (the fine LES). We intended to resolve the turbulent boundary layer (TBL) developed on the surfaces of impeller blades and diffuser vanes in the fine LES. We obtained a good agreement between the measured and predicted pump performance for a wide range of flow rate in the coarse LES, although the predicted total head drop at the flow rate of 55%∼60% is smaller than the measured one. In the fine LES, accuracy of pump performance prediction at 55%∼60% flow rate was improved.Copyright

Large Eddy Simulation and Acoustical Analysis for Prediction of Aeroacoustics Noise Radiated From an Axial-Flow Fan

A final objective of this study is to develop a tool to predict aeroacoustics noise radiated from a low-speed fan, and its reduction. Aeroacoustics noise that is radiated from a low-speed axial flow fan, with a six-blades rotor installed in a casing duct, is predicted by an one-way coupled analysis of the computation of the unsteady flow in the ducted fan and computation of the sound radiated to the ambient air. The former is performed by our original code, FrontFlow/blue, which is based on Large Eddy Simulation (LES). The latter is performed by using a commercial code, SYSNOISE, which computes the sound fields in the frequency domain. The following three cases of computations are performed for LES with different flow field configurations and/or grid resolutions: a coarse mesh without the struts located, in the actual fan, upstream of the rotor blades, a fine mesh without the struts, and a coarse mesh with the struts. The first two test cases are intended to investigate the effects of the mesh resolution on the prediction accuracy of the unsteady flow field, especially we intended to capture unsteadiness in turbulent boundary layer (TBL) in the second test case with the computational mesh composed of about 30 millions hexahedral elements. The fine mesh LES successfully reproduced the transition to TBL on the suction surface of the rotor blades and gives better, when compared with the results from the coarse mesh LES, agreements with measurements in terms of Euler’s. The final case is used for providing acoustical input data of the sound source. A reasonable agreement is obtained between the predicted and measured sound pressure level evaluated at 1.5 m upstream of the blade center.Copyright

Cooling efficiency aware workload placement using historical sensor data on IT-facility collaborative control

A priority metric for IT equipment is proposed, and a method for extracting it from historical sensor data is devised. The proposed method consists of classification of cooling efficiency from sampled sensor data and calculation of the priority metric from statistics on these cooling-efficiency classes. A proof-of-concept experiment using the priority metric was conducted in a server room with a thermal environment including IT equipment units and cooling facilities. The results of the experiment indicate that IT-workload consolidation based on the proposed metric equalizes variation in server-room temperatures.

Estimation Method of Temperature Distribution and Energy Saving Technology of Air Conditioner in Data Center

Reducing the energy consumption of a data center has recently become important because the data center market is rapidly expanding. We developed the “IT-facility linkage system” to deal with this energy saving requirement. This system reduces the amount of energy consumed in a data center by linking two systems, one is the optimized server load allocation system and the other is the air conditioning optimization control system. One of the key technologies of the “IT-facility linkage system” is the precise prediction of the server inlet temperature. If we can comprehend the future temperature distributions, we can reduce the amount of energy consumed in a data center by consolidating the IT load to the more effectively cooled servers. We carried out computational thermal fluid dynamics to predict server inlet temperatures and evaluated the prediction precision by comparing the measured temperature data for this paper. As a result, we found out that when we use a detailed rack model and reproduce the characteristic air flow of a data center such as the recirculation, we can precisely predict the server inlet temperature to within less than one degree.Copyright