Using CFD to Optimize Wind Noise in a Car’s Cabin
Shawn Wasserman posted on December 16, 2016 |
CFD results of fluctuating surface pressures can be used to assess the vibrations in the car frame that cause noise within the cabin. (Image courtesy of ESI Group.)

CFD results of fluctuating surface pressures can be used to assess the vibrations in the car frame that cause noise within the cabin. (Image courtesy of ESI Group.)

Over the years, automotive engineers have done a great job in reducing the car noises that can distract and irritate drivers. Engine, tire and muffler noises have all been reduced, improving the perceived quality of the product and driver comfort.

The problem is that they may have done too good of a job. Today, wind has become one of the major contributors to the noises we experience when driving.

Wind noises can impact how a driver socializes with passengers, their communication with hands-free devices and their overall opinion of the vehicle. As a result, this Aero-Vibro-Acoustics (AVA) problem, known as wind noise, is a significant factor the automotive industry must understand to improve the user experience.

However, this issue isn’t limited to the automotive industry—just look at the aerospace industry. There is nothing worse than needing to get some work done on a plane, but finding the roar of the wind to be too loud to concentrate. Needless to say, the effects of AVA are a significant challenge for a range of industries.

“With wind as the next dominant noise contributor, this stimulates an interest in finding cost-effective simulation solutions,” says Trevor Edwards, director of sales in Europe at ESI Group. “These simulations avoid the use of scarce, expensive, hard-to-repeat and time-consuming wind tunnel studies.”

To assess the noise in the cabin properly, engineers need to propagate the pressure-based turbulent computational fluid dynamics (CFD) results through the solid car frame. This can be done with simulation technology like ESI Group’s VA One Aero-Vibro-Acoustic model.

 

Performing an Aero-Vibro-Acoustic Study with Simulation

ESI VA One is a full-frequency simulation software that is designed to solve various noise and vibration problems. The program is able to set up a Multiphysics simulation that incorporates CFD, finite element (FE), boundary element (BE) and statistical energy analysis (SEA).

Aero-vibro-acoustics workflow sees engineers post-process the source data. CFD surface pressures are detected for the specified region. Data is imported, processed and visualized into noise results in ESI Group’s VA One. (Image courtesy of ESI Group.)
Aero-vibro-acoustics workflow sees engineers post-process the source data. CFD surface pressures are detected for the specified region. Data is imported, processed and visualized into noise results in ESI Group’s VA One. (Image courtesy of ESI Group.)
Using the software, engineers can convert their CFD pressure distributions time histories into fluctuating surface pressure loads, or input power into the frequency domain. The wavenumber spectra are then applied onto the SEA model directly. After that, the preprocessing tools can extract the CFD data and apply the loads onto the model.

These loads, both convective and acoustic, are then tested on the structures and fluids in the car frame to assess the noise within the cabin. Engineers can use this data to optimize a car’s design by minimizing the noise within the car.

The workflow could be summarized as:

  1. Select and post-process the source CFD data
  2. Export the CFD model at the location of study over the selected time steps
  3. Import CFD data into VA One
  4. Solve the model and visualize the AVA results

The Benefits of Modern Aero-Vibro-Acoustic (AVA) Simulations

The turbulent flow around the car’s mirror can be added into an AVA study to assess its impact on the interior noise of the car. (Image courtesy of ESI Group.)

The turbulent flow around the car’s mirror can be added into an AVA study to assess its impact on the interior noise of the car. (Image courtesy of ESI Group.)

ESI explains that previously, SEA models were created by assessing turbulence results using an analytical model. The problem with these models was that sometimes the details were lost in translation.

“In the past, AVA simulations were difficult due to the need to couple CFD time history data with sufficient resolution to define an event with Vibro-Acoustic prediction software,” says Edwards.

“Part of this difficulty lay in the need for large CFD calculations to capture enough of the event history and tools that could extract from the event history the excitation needed to perform the acoustic calculation,” Edwards adds.

This created a dilemma for engineers, as they had to choose between data accuracy and modeling the AVA problem. Modeling can prove difficult and it can be costly. Wind tunnels, in contrast, can be hard to schedule, costly and make it hard to replicate results.

Edwards explained that CFD technology and computer processing have advanced to the point where engineers can now capture enough of the historical turbulent and time domain data to support the study of wave propagations through the solid frame of the car.

Additionally, tools and algorithms which are used to extract the information—such as VA One’s general surface pressure (GSP) model—and are needed to perform the Vibro-Acoustics wave propagation studies, have also seen improvements in the last few years. As a result, it has become more cost-effective to achieve accurate noise simulations without the need for a wind tunnel.

As for the direct benefits of VA One itself? ESI starts with the fact that its user interface (UI) is intended to help democratize the simulation process. The UI is designed to allow engineers to learn the software quickly with minor training. It is also organized in a way to help minimize model building time and model couplings.

Additionally, ESI explains that VA One is optimized for multi-core processing. This helps speed up the program’s read, write and solver functions. As a result, engineers will be able to run a large number of simulations early in the development cycle and in the short time frame that automotive engineers have to create a product. This means that engineers will be able to run numerous design variations, which will allow them to make more informed decisions early-on, reducing the need for expensive redesigns late in the product’s development.

VA One is also capable of performing other acoustic simulations, including non-uniform acoustic FE mean flows and multi-core boundary element method calculations. To find out more about ESI VA One, follow this link.

ESI Group has sponsored ENGINEERING.com to write this article. It has provided no editorial input. All opinions are mine, except where quoted or stated otherwise. —Shawn Wasserman

 

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