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Keihin Corporation
Performing Aerodynamic Noise Analyses to Meet Demands for Noise Reduction

As EVs and HEVs (hybrid and electric vehicles) become more common, the need for quiet and highly efficient vehicle HVAC (Heating, Ventilation, and Air Conditioning) equipment has become increasingly important. Noise reduction is critical for air-conditioning equipment and tools using fans to move air. Keihin Corporation uses SC/Tetra to conduct aerodynamic noise analyses to identify noise sources and evaluate countermeasures to reduce noise levels. Using computational tools to predict noise is extremely complex and is considered a very challenging flow simulation application.

Conducting Frequency Analyses to Identify the Source of Noise

 When Keihin Corporation first introduced SC/Tetra, the tool was only used to evaluate the air flow field. Now they have extended its application to aerodynamic noise analyses.

Fig 5 Example of an aerodynamic noise analysis at the opening for the blower motor cooling air flow path: relocating the opening reduced peak noise levels. Click to enlarge.

 Aerodynamic noise analysis requires highly accurate calculations because the sound pressure differences are only a few Pascals at most. LES (large eddy simulation) is used for turbulence modeling on a 48-core machine. Using the aerodynamic noise analyses, Keihin Corporation identified the sound source and improved the geometry of the blower to reduce the noise. The analysis identified the problem emanated from the small air inlet at the bottom of the blower, which is used for cooling the motor. A 1500Hz frequency noise was detected in a prototype test. Keihin Corporation performed analysis to visualize the air flow and found that periodic eddies were generated at the air inlet, as shown in the vector diagram in fig 5. According to the flow analysis, eddies were created 1500 times per second (1500Hz) which agreed with the observations from the experimental tests. Based on the hypothesis that the turbulence eddy formation rate at the cooling air inlet was the primary source of noise, Keihin engineers relocated the air inlet and performed the simulation again. The results showed a more uniform flow, and the disappearance of the previously-detected periodic eddies. The 1500Hz peak frequency no longer existed. Keihin engineers produced a revised prototype that incorporated the improvements from the simulation results, and successfully eliminated the noise.

Fig 6 Example of how fluid analysis is used to identify the sound inside the heater unit: noise occurs when air is transferred through the gaps. Click to enlarge.

 Fluid analysis has also been used to develop measures to eliminate the noise generated when transferring the air to the heater unit (fig 6). The Heat/Defroster mode in the vehicle air-conditioning system directs conditioned air to the windshield and heated air to the passenger footwell simultaneously. Noise was generated from the small gap between the sliding doors that opened and closed to control the warm air from the heater unit and the cool air from the evaporator. Keihin engineers conducted a fluid analysis to identify the noise source which helped them construct countermeasures.

Improving the Simulation Environment for Better Analysis

 Keihin Corporation aims to provide industry leading hardware and facilities so their design engineers and CFD specialists can learn to use the analysis tools and fully utilize their capabilities. When SC/Tetra was initially introduced Keihin Corporation only had a few CFD specialists. Now the number of specialists has grown to three times greater. Selected engineers specifically work with noise reduction of the overall blower and inner heater unit. Their challenge is to improve and develop the tools, environment, and entire system so more design engineers can easily and flexibly perform the analyses.

Easy Mesh Generation of a Blower is a Key Factor

 Keihin engineers found SC/Tetra suitable for meeting their simulation objectives, which were to perform blower transient analysis and conduct aerodynamic noise analysis. However, the primary reason they initially selected SC/Tetra was its ease of preprocessing (geometry preparation and mesh generation). They tried other simulation tools for the early blower simulations, but they were not able to generate boundary layer elements around the vanes, even after reducing the number of vanes to simplify the model. As a result they could not accurately calculate the pressure in the blower. After several unsuccessful attempts to mesh boundary layer elements around the vanes, they tried SC/Tetra. Using SC/Tetra they found that mesh generation, including the boundary layer elements, could be done quickly and effortlessly.

 “Another reason we chose SC/Tetra was that it was much faster,” says Mr. Onodera. From previous experience, Keihin engineers were aware that simulating a blower was time-consuming. When they switched to SC/Tetra, analysis time was reduced to one third with the same hardware specifications, and the accuracy of the results did not change.

Separating Each Sound

 Several functions were added to SC/Tetra to support Keihin engineers’ pursuit of better aerodynamic noise analysis. In SC/Tetra Version 9, only a compound waveform could be calculated, making it impossible to separate individual sounds. When Mr. Onodera and his engineers asked Software Cradle for additional support, an interim solution was proposed to simulate a compound waveform from various observation points and to estimate a particular sound from the shape differences. SC/Tetra Version 11 has since advanced to where it can separate sound pressures for each sound using a single observation point. As the waveform cannot be separated into individual sounds from experimental data, this analysis function is extremely beneficial for Keihin engineers.

 “Not only were they quick to incorporate our requests regarding software functions, but Cradle engineers were also very responsive with their everyday support. This is another benefit that comes with using Cradle software,” comments Mr. Onodera.

Aiming to Evaluate the Overall System through Coupling

 Keihin engineers are eager to continue using simulation as a part of the production process. Although their CFD specialists are currently the only ones using SC/Tetra, Keihin Corporation has a longer term goal of making the tool available to more engineers. They want to increase the number of software licenses, prepare manuals to train their engineers to learn the operations, and develop automated tools to facilitate blower fluid analyses. This work has already been initiated as Keihin engineers started using the Cradle Visual Basic Interface to automate calculation processes and have also started receiving Cradle–led training.

 Keihin Corporation has expanded the boundaries of CFD to make their design tasks more efficient. SC/Tetra has played a critical role in contributing to Keihin Corporation’s improved product development.

*All product and service names mentioned are registered trademarks or trademarks of their respective companies.
*Contents and specifications of products are as of April 30, 2011 and subject to change without notice. We shall not be held liable for any errors in figures and pictures, or any typographical errors.

Company Details


Keihin Corporation
Founded December 1956
Business Manufacturing of vehicle components
Representative Tsuneo Tanai, President and CEO
Location of Head Office Shinjuku-ku, Tokyo, Japan
Capital Approx. 6.9 billion JPY
​(as of March 31, 2013)



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