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Kogakuin University (Faculty of Global Engineering, Department of Innovative Mechanical Engineering)
Thermal-fluid Analysis Tool Highly Favored by Students to Pursue Research of Synthetic Jet

[Vol. 2] The Fluid Machinery Laboratory at Kogakuin University uses the SC/Tetra thermal-fluid simulation tool. The tool is vital for deepening the understanding of fluid characteristics by faculty and students in the laboratory, and helps advance the research at the laboratory where experiments and simulations are performed simultaneously. Professor Kotaro Sato explains that, thanks to the tool's easy operability and highly extensive support from the developer, student interest in research has expanded.

Unexpected Results from an Analysis of an Axial Fan

Professor Sato’s laboratory also investigates flow characteristics of axial fans. A general-purpose fan, which is often used in electronics, is normally developed assuming ideal design conditions. Professor Sato thought “why shouldn’t a fan perform better in an unfavorable environment,” and decided to start investigations.

In fact, fans are rarely exposed to ideal conditions. In computers, fans are often lined up along a wall side by side altering and restricting air flow, and fan filters are seldom replaced. Using a general-purpose fan has a cost advantage compared to designing a special fan for a particular application. In some cases, such as fans used in vehicle air-conditioning systems, specially designed fans are still needed. But the trend toward using general-purpose fans, when possible, is growing. When general-purpose fans are used, useful design information would include the minimum allowable distance from obstacles and quantification of performance degradation due to the presence of obstacles.

As his axial fan research progressed, Professor Sato found that unexpected vibrations occurred under certain operating conditions. Professor Sato also encountered other phenomena he was unfamiliar with, such as improved flow characteristics when an obstacle was located at the outlet or flow reversal when an obstacle was allocated at the inlet.

Fig 6: (a) Surface pressure distribution on the blades and velocity vector diagram on the middle cross section of the fan, with a spherical obstacle 320 mm in diameter located 5 mm from the fan. (b) Surface pressure distribution on the obstacle, and velocity vector diagram at the mid position between fan and the obstacle. Click to enlarge.

Fig 6 shows the results of an analysis for conditions when the unexpected vibrations were detected. Fig 6 (a) shows the surface pressure distribution on the blade and the velocity vector diagram at the middle cross section of the fan, which is 130 mm in diameter and rotates at 2,500 rpm. The calculations were based on a hypothetical condition that a spherical obstacle 320 mm in diameter was located 5 mm from the fan. Fig 6 (b) shows the surface pressure distribution on the obstacle, and velocity vector diagram at the mid position between the fan and the obstacle. The pressure distribution indicates a compartmentalized disturbance, where areas with high and low pressures alternately align. The disturbance rotates 0.1 to 0.2 times as fast as circumferential speed of the fan. This unstable flow was first detected in an experiment, and later reproduced in numerical simulations using SC/Tetra. The simulation results verified that the phenomena could occur with other devices as well, and was not caused by vibrations particular to the device used in the experiment. The severity of the phenomena correlates with fan size. Devastating effects, such as overheating the fan bearing, can be caused. For smaller fans, the vibration may result in unnecessary noise and reduced life. Professor Sato continues to conduct axial fan investigations to better understand the mechanism causing the vibrations.


Tool Highly Preferred by Students

Previously, Professor Sato’s laboratory used another computational analysis tool that was difficult to use and incurred costly support fees. This limited the number of users, which hindered students from pursuing research as extensively as they wished. Unsatisfied with the tool at the time, the students identified SC/Tetra and decided to install the software in 2002. They were pleased that SC/Tetra produced accurate analysis results, and they received excellent technical support. With SC/Tetra, the students can now perform analyses as often as necessary and in a short amount of time. As a result the students are more eager to use the tool during their research. Professor Sato considers the students’ opinions when installing tools in the laboratory. If the tool can be easily used, the students will focus more on the research rather than spending time learning how to use the tool. Another benefit of SC/Tetra is its capability to visualize results. This inspires the students’ fascination with fluid dynamics. The students also appreciate the guidance given at seminars and training sessions organized by Software Cradle. Software Cradle also provides guidance on how to use the software in unconventional situations.
 

Future Challenges: Calculation of Gas-liquid Two-phase Flow and Coupling Analysis

In the future, Professor Sato hopes to explore gas-liquid two-phase flows and coupled analyses between fluids and an elastic body. As an example of a gas-liquid two-phase flow, Professor Sato has been investigating the flow field downstream of a heat pump compressor. He hopes to gain understanding about the separation mechanism for oil mist in refrigerant. Heat pumps, such as those used in air conditioners, use centrifugal force to separate oil from the refrigerant, but the detailed mechanism still remains unexplained. If the physical mechanisms driving oil separation in refrigerants can be understood, this will lead to improved product designs, shortened development cycles and improved product performance.

The high rotational speeds of a heat pump compressor, as high as 10,000 rpm, could result in failures and potentially damaging accidents during operation. A coupled analysis will enable predicting the frequency where the risks of failures and greater accident damage are heightened, so that the equipment can be operated away from the critical frequency.

​​*All product and service names mentioned are registered trademarks or trademarks of their respective companies.
*Contents and specifications of products are as of February 1, 2015 and subject to change without notice. We shall not be held liable for any errors in figures and pictures, or any typographical errors in this brochure.

Institute Details






 

Faculty of Global Engineering, Dept. of Innovative Mechanical Engineering
Founded 1949
Type of university Private
Professor Kotaro Sato (Doctor of Engineering)
Location Shinjuku-ku, Tokyo, Japan
URL http://www.kogakuin.ac.jp/another/hp/ge/

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