Choosing the Right Silencer: Why BAR Arrays Outperform Parallel Baffles

Exhaust system performance depends on efficient flow path definition, component durability, material and design precision, and ideal silencer integration, which, in turn, optimizes flow losses and noise attenuation. When comparing absorptive silencer types, parallel baffles, concentric baffles, and acoustic BAR arrays all offer advantages in turbine exhaust noise control and long-term reliability. Historically, however, absorptive BAR arrangements with individual square, rectangular, or round cross-sectional profiles have been shown to be exceptionally efficient, achieving high attenuation per unit of active length. Experience in jet engine test cell design, combined with more recent powerplant field experience and modeling work, has revealed that acoustic BAR arrays or BAR silencers can resolve several challenges common to traditional parallel or concentric baffle systems, especially under turbulent or rotational flow conditions.

Flow Behavior and Distribution

Parallel and concentric baffle silencers restrict airflow to narrow paths between baffles, which limits the flow's ability to redistribute dynamically. Commonly, these arrangements reveal regions or zones of high velocity flow, requiring additional structural considerations and infill protection schemes. Parallel or concentric baffles tend to confine exhaust flow to channels, limiting dispersion to two dimensions: axial (along the duct length) and within defined passages.

In contrast, BAR silencers allow for three-dimensional distribution. Explained more fully, this is a matrix or array of absorptive BARs that allows exhaust flow to move freely in multiple directions, generally less restricted by the available duct cross-section. The difference in BAR silencer flow behavior is not just academic; it directly affects silencer performance and equipment loading conditions resulting from elevated static and dynamic pressures.

Due to the rotational nature of turbine exhaust flow, lateral or side load conditions can exist in a horizontal or vertical exhaust configuration. The BAR silencer approach helps mitigate the effects of side loading and general turbulence, particularly in systems with limited silencer approach length or high-velocity flow. To date, SVI Dynamics has deployed BAR silencer arrangements in several challenging aerodynamic exhaust environments, resolving pre-existing equipment failure problems.

Acoustic Performance

BAR silencers offer flexible acoustic tuning by controlling favorable geometrical configurations, wetted surface area exposure, and flow-induced loading patterns. Compared to concentric or parallel baffle systems, the BAR matrix offers superior management over the distance between and the thickness of absorbing layers, leading to greater overall noise reduction from the silencer’s inlet to outlet.

Additional benefits include extending attenuation to lower frequencies compared to conventional parallel-baffle arrangements. BAR matrices allow for the optimization of cross-sectional space, introducing thicker absorptive layers throughout the design. In turn, the silencer design becomes more effective at low frequencies, particularly at the 31.5, 63, and 125 hertz full-octave bands. Each BAR interacts with the sound field on four surfaces, along with a diagonal to treat some lower frequencies with longer wavelengths. This configuration makes it easier to manage acoustic energy across a broader spectrum.

Self-Generated Noise and Durability

Because the BAR silencer optimizes the available cross-sectional flow area, it generally reduces average and peak exhaust flow velocities, which, in turn, minimize turbulence along the BAR boundary layer. By reducing kinetic energy, any self-generated flow noise in this environment is less in magnitude.

The improved flow uniformity also reduces mechanical stress and the risk of damage to silencer components over time, contributing to greater system durability and lower maintenance requirements.

Implementation Benefits

In general, design flexibility and performance maximization enable BAR silencers to be integrated into aerodynamically restricted spaces without sacrificing performance. SVI Dynamics manages the distance between and the thickness of absorbing surfaces in order to increase noise attenuation per unit active length. Oftentimes, this characteristic leads to a reduced, integrated silencer package length and translates to additional duct length for exhaust flow moderation. In these ways, the BAR silencer is known to improve the aerodynamic and acoustic properties of exhaust systems, particularly those with limited or restricted dimensions.

Field Results

Results in the field have confirmed SVI Dynamics’ theoretical and boundary-element-method (BEM) modeling results. A baseline measurement from July 2023 indicated effective noise control with slightly better low-frequency performance. At a distance of 400 feet, SVI BREMCO measured a GE 7FA exhaust stack emitted an overall sound pressure level at 58 dBA, a value significantly lower than the ambient noise generated by nearby traffic.

Conclusion

BAR silencers offer a practical, technically justified upgrade over concentric and parallel baffle designs in modern turbine exhaust systems. Their ability to manage complex flow and treat a wider acoustic range makes them a valuable solution for operators seeking to improve system longevity and regulatory compliance.

About the Author

Tucker York is the Director of Acoustical Engineering for SVI Dynamics and a graduate of Michigan Tech. He has nearly 37 years of experience working in noise control engineering with different types of turbines, from power turbines to aero derivatives and jet engines, developing effective solutions for customers.