Noise is a big problem in commercial and agricultural vehicles all around the world. While it is important for drivers to hear the sound of an engine, noise that is too loud can be uncomfortable.
Government regulations on commercial and agricultural vehicles are heavy and also change from one country to another. For example, while regulations are very strict in Europe, they are comparatively light in India, and this makes it difficult for Indian companies to sell in Europe.. This was the case when CNH was faced with tight new regulations in a key Latin American country. They were asked to reduce the noise level of their machinery to the allowed decibel point regarding the machine’s size and power.
To overcome this challenge, CNH ran some physical tests on their products and they eventually found out that the significant amount of the noise comes from the fan. Since the engine was big in order to generate the power needed for machine, fans are also huge to cool the hardworking engine. CNH realized that repetitive physical tests resulted in waste, were too costly, took too much time, and provided limited data that would cause engineers to rely more on assumptions and guesses.
CNH realized the importance of CAE in making product development faster and less costly, but the FEA and CFD tools that they were using were not sufficient to solve their new noise problem. A more advanced solution was needed due to the complexity of acoustics.
“We have for a long time been able to simulate noise sources with computational fluid dynamics (CFD) but we did not have an accurate method to simulate the propagation of noise generated by these sources” said Dr. Panos Tamamidis, Global Manager, CFD, NVH and Acoustics for CNH Industrial.
After testing the problem in Actran, engineers at CNH saw the results were much more accurate than those provided by physical testing and they understood everything that they needed to fix in the fan. They found out that the biggest part of noise was coming from blade-pass frequency and a comparatively smaller amount is also coming from broadband noise.
After trying many different fan styles, blade types, various combinations of them and applying CFD iterations and acoustic simulations for each time, they found an effective solution that provides needed reduction in blade pass frequency and also broadband noise at the same time. Actran was also used to find an efficient muffler design that would contribute to solution. Due to their use of acoustic simulation, CNH was finally able to meet the new regulatory requirements.
“Simulating the acoustic performance of alternative approaches to noise remediation helped us meet the tighter noise specification in about three months” Tamamidis said. “If we had to rely on physical testing for this project, it would have taken at least a year to reduce noise to the levels needed to meet the new spec. Due to successful projects such as this, we have integrated Actran into our product development process and use it on a regular basis to help ensure the acoustic performance of new designs and solve problems with existing designs. “