How CFD Reduces NVH in Automotive Designs

One always remembers their first time sitting behind the wheel of a luxury vehicle and taking it for a spin. The first thing you typically notice is how smooth the ride feels and how quiet the interior of the car sounds. What makes that experience notable is the analysis of NVH, otherwise known as Noise, Vibration, and Harshness. This study is particularly relevant today as the popularity of Electric Vehicles (EV’s) continues to rise. With EV motors being far quieter than internal combustion engines, many new noise sources can now be heard.

What Exactly is NVH and Why Does it Matter?

In the automotive industry, NVH plays a significant role in the overall driving experience and comfort of a vehicle. It refers to undesirable sounds and vibrations that passengers can observe inside a moving vehicle. NVH is influenced by several factors including engine vibrations, road conditions, tire noise, and aero acoustic noise sources. For instance, older vehicles might have an engine vibration which can cause both noise and harshness that can be felt as a slight rattling. Or, in some vehicles you may hear more wind noise when driving at high speeds on the freeway.

Excessive NVH can cause driver fatigue and discomfort, resulting in negative feelings that the vehicle is poorly constructed or cheap. High-end cars often feature advanced noise reduction technologies, such as double-glazed windows or special damping materials, to minimize noise and vibrations.

NVH in ICE Vehicles vs. Electric Vehicles

When it comes to the sounds and vibrations we feel while driving, EV’s and Internal Combustion Engine (ICE) vehicles have some key differences.

Sources in ICE Vehicles

In ICE vehicles, NVH is dominated at low speeds by the engine’s combustion process—think engine noise from the pistons and fuel ignition, along with sounds from the exhaust and intake systems. Add in the vibrations from the engine and mechanical transmission, and you’ve got a much noisier and more vibration-prone ride.

Sources in EV’s

EV’s, on the other hand, are quieter by nature, thanks to the absence of a combustion engine, frequently associated with a simpler transmission. While this may sound like a good thing, it actually presents its own set of unique challenges. In ICE vehicles, the engine often masks other noises but with EV’s the absence of an engine makes other noise more apparent. The most prominent noises are road noise and wind noise. However, EV’s also experience noise from electronics, HVAC, electric motor noise, and noise from gearsets and cooling pumps.

The NVH Analysis Process

It may come to no surprise that NVH Analysis involves a myriad of different steps, measurement, analysis, and simulation to produce accurate results. What’s the goal for NVH analysis? To reduce unwanted noise and vibration resulting in a comfortable, quiet, high-quality ride. With that in mind, here’s a breakdown of the NVH Analysis process:

Data Acquisition – The journey begins with gathering data. Engineers use a variety of tools to capture the full spectrum of what is heard and felt during a drive: microphones to capture sound, accelerometers to measure vibrations, and other sensors to track forces and loads. These measurements are taken in diverse environments, from controlled labs to real-world driving scenarios.
Analysis – Once the data is collected, the real detective work begins. Engineers need to understand why things vibrate and make noise. This involves techniques like modal analysis, which reveals the natural frequencies of a vehicle’s components, and frequency analysis, which breaks down complex sounds into their individual tones.
Simulation – Modern engineering relies heavily on computer simulations. Engineers use Finite Element Analysis (FEA) to model how components vibrate and Computational Fluid Dynamics (CFD) to predict aerodynamic noise. This allows them to test design changes virtually, saving time and resources.

CFD’s Impact on Noise, Vibration, and Harshness

By simulating airflow around and within vehicles, CFD allows engineers to pinpoint sources of aerodynamic noise, such as turbulent flow around side mirrors or windshields or from an open sunroof. Specifically, CFD can:

Predict Aerodynamic Noise: CFD simulations can accurately predict the generation and propagation of wind noise, allowing engineers to identify and address areas of concern early in the design process. For example, simulating flow separation around A-pillars and side mirrors can reveal potential noise sources.
Optimize Vehicle Shape: By visualizing and analyzing airflow patterns, engineers can optimize the vehicle’s shape to minimize drag and reduce wind noise. Changes to the vehicle’s body shape, spoiler design, and underbody components can be evaluated and refined using CFD.
Analyze Internal Airflow: CFD is crucial for understanding and optimizing the performance of HVAC systems. By simulating airflow within the cabin, engineers can reduce noise generated by fans, ducts, and vents, ensuring a comfortable and quiet interior environment.
Aeroacoustics: By coupling CFD with acoustic models, engineers can directly predict the noise generated by turbulent flows. This allows for a more comprehensive assessment of aerodynamic noise and the effectiveness of noise reduction measures.

Leveraging Tecplot for NVH Analysis

Our CFD post-processing tools, like Tecplot 360 and FieldView, empower engineers to delve deep into their simulation results, extracting valuable insights that drive innovation. Whether you’re analyzing aerodynamic noise around a vehicle’s exterior or optimizing airflow within the cabin, our tools can help you make informed decisions and reduce NVH. By leveraging Tecplot’s products, automotive engineers can streamline their NVH analysis workflows, reduce development time, and deliver vehicles that exceed customer expectations.