Showcasing the Silencer

Over the next couple of weeks we’ll be showcasing various different parts of the car! The designer of each part will talk you through their design decisions, helping you understand the process. First up, it’s Ryan and his Silencer!

Name: Ryan Clark

Sub-team: Powertrain

Part: Silencer

What is the purpose of the component? The purpose of the silencer is to make sure the car is quiet enough to pass the noise test. The rule regarding this states that the maximum permitted sound level is 110 dB(C) an 11,000 RPM, so the silencer aims to attenuate enough of the noise produced by the engine so this value is not exceeded.

What are the specific features of your design? The main change this year was the change of the geometry inside the can. Instead of having a straight pipe through the can, the perforated pipe has two bends in it. This was done in order to increase the sound attenuation of the component, whilst not being restrictive enough to limit the power very much. An image of this, in the software package, and the product received from the manufacturer, can be seen below.

What were the challenges to overcome? The largest challenge faced was the lack of knowledge within the team; this was the first year that someone was specifically tasked with designing the silencer.  As it was now being considered with larger importance, it was challenging to teach myself not only how to use the software package to its full extent, but also the theory behind the acoustics involved in the problem.

Which simulations did you carry out? So far, many simulations have been carried out which pointed towards the bent tube design, with a screenshot attached below.

The graphs plot engine speed, in revolutions per minute, against measured sound level, in dB(C). This curve was produced by the software Ricardo WAVE, and shows the sound level produced by the car as the driver revs the engine higher. The blue line is the sound profile of the silencer used by UGR-18, last years car, and the green the so called “bent tube” silencer. Although the graph does not predict it will be 110 dB(C) or less when it reaches 11,000 RPM, WAVE has not been 100% accurate in its predictions. To combat this, a sound drop of 6 dB was aimed for, as UGR-18 was 6 dB over the permitted level. This bent tube achieves a drop of 8 dB, which should put it below the maximum level. The next step is to test the design on the car and see how closely the results tie in with those achieved in the simulations.

What are the main improvements from previous years? The can is made from aluminium rather than stainless steel, meaning it is significantly lighter. The can is attached to the endplates by rivets, rather than the welding used last year, making it far easier to dismantle the silencer if we need to. The bent tube design discussed earlier will help the silencer attenuate more noise than previous years.