The sound of silence, or at least something very close to it, is a valuable asset. As consumers become ever more discerning, they also become more sensitive to the noise products generate. Increasingly, that means manufacturers of everything from washing machines to air conditioning units are trying to find ways to design quieter products.
In many respects, the automotive sector has been the trendsetter in sound minimization. Back in 1957, the so-called “Father of Advertising” David Ogilvy created a now legendary slogan for Rolls-Royce: “At 60 miles an hour, the loudest noise in this Rolls-Royce comes from the electric clock.” In the middle of the last century, a quiet automobile was the preserve of a lucky few. Today, car buyers of all stripes – no matter how luxurious the model – expect a quiet ride. The same principle applies for all other kinds of consumer goods as well.
With OEMs looking to boost their products’ appeal by minimizing noise, many more are now investing in new end-to-end CAE and noise, vibration, and harshness (NVH) workflows that promise not only better design outcomes, but greater speed and cost efficiency too. Where wind noise is involved, the latest computational fluid dynamics (CFD) tools offer compelling advantages. For example, Altair® HyperMesh® CFD enables users to mesh a product model swiftly and accurately, test it in a virtual wind tunnel to simulate air flow, and even simulate the noise it will generate. Designers can then easily tweak and test different iterations until a quiet hero emerges.
It's an approach that resonates across a plethora of industries, products, and applications. To dig deeper into the benefits, let’s consider how this new generation of tools is transforming acoustic design approaches in the aforementioned automotive sector and providing a solution to noise pollution.
Whistling in the Wind
From behind the wheel of a car, we experience noise from a variety of sources. These include the engine and drivetrain, the contact between the tires and road surface, the fans whirring away behind the dash, and more. Greenhouse noise (GHN) is another significant issue. This is the sound heard inside the vehicle, which is produced by turbulent air flow over the vehicle’s exterior surfaces. Perceptible between the frequencies of 500 Hz to 10 kHz, GHN becomes vehicles’ dominant noise source at highway speeds and gets louder the faster a vehicle is moving.
In terms of vehicle design, there are plenty of GHN hotspots. The most notable is the point at which the side mirror interacts with the vehicle’s A-pillar. This can generate intense vortices that are likely to produce unwanted noise. Another GHN hotspot is hood styling features that influence the airflow at that same junction of side mirror and A-pillar. The rain gutter and cowl can also add noise. Overall, GHN is still an important consideration for car buyers and the OEMs competing for their business. After all, quieter electric vehicles (EVs) are replacing noisier internal combustion engines, and, as more lawmakers pass hands-free laws, consumers want vehicles in which GHN doesn’t interfere with their calls.
One solution to noise pollution brands have adopted is to add laminated glass or double glazing in areas like the windshield and driver’s side window. However, this inevitably increases build cost. In addition, the extra weight and mass increase fuel consumption and dampen battery range. As such, manufacturers are turning their attention to the causes of GHN, rather than the symptoms.
Light at the End of the Tunnel
Traditionally, automotive OEMs (as well as heavy truck, train, and aircraft manufacturers) have tested, observed, and addressed unwanted noise via acoustic wind tunnels. However, these are highly specialized facilities. Acoustic wind tunnels cost tens of millions of dollars to build and tens of thousands of dollars to rent for just a few hours. In addition, creating and then refining the physical prototypes tested inside them can be costly and complex. And on top of it all, processing the data generated by wind tunnel testing is yet another demanding, resource-intensive task.
This approach poses further problems for designers looking for a solution to noise pollution. By the time the development cycle reaches physical prototyping, other design considerations are already likely to have taken precedence. In the case of an automotive design, aerodynamic optimization usually comes first, since it has a major impact on key performance characteristics like fuel efficiency and battery range. With these higher priorities already baked into the physical prototype, it becomes harder still to argue for the additional time and resources required to implement changes to meet acoustic goals.
Working in Harmony
All of this strengthens the case for the latest solvers that can mitigate unwanted noise within these constraints and conditions. Within the Altair® HyperMesh® CFD environment, these include Altair® ultraFluidX®, which delivers lightning-fast prediction of the aerodynamic properties of passenger and heavy goods vehicles, and solutions for NVH that help predicts interior noise levels. Crucially, these solutions to noise pollution do more than just enable teams to consider noise at a much earlier stage in the process. They also allow closer collaboration between aeroacoustics and aerodynamic engineers, as well as the many other disciplines and design factors that must be reflected in the final outcome. With everyone using the same virtual design environment, product development becomes a more cooperative, more harmonious process. Instead of competing for a place in a linear sequence of priorities, different design disciplines can work in something like a team huddle. As a result, this type of software is creating exciting new opportunities for innovation.
It's important to keep in mind that, while GHN can be a very technical problem, it’s solving real-world issues consumers deal with every day. People care about noise and don’t want to endure it if they don’t have to. According to Quiet Mark, a British certification body, 49% of British consumers consider sound an important factor when buying home appliances or kitchen tabletop electricals. In a 2019 JD Power Survey, owners who reported their vehicles were “very quiet” were over 50% more likely to repurchase the same brand when compared to those who found their vehicles to be too noisy. With the help of CFD and CAE software, it’s now easier than ever to deliver products that meet customers’ high expectations for quiet products. What’s more, they can do so within an environment that supercharges the entire design process, making it both more efficient and more creative than traditional methodologies built around physical wind tunnels and prototypes. For OEMs looking to deliver quieter, more compelling products, that must sound like music to their ears.