Numerical Simulation Of Three-dimensional Flow In Muffler

Flow has a big influence on the noise elimination capability and the air dynamical capability of the muffler. There are two ways to affect the capability of the muffler. First, the air flow makes the condition of the muffler to be different. Second, because of the onflow of the air flow ,it makes some regeneration noise. The regeneration noise mostly lies on the velocity of the air flow and the construction of the muffler. The aerodynamic capability is a very important guideline for estimating the muffler. If a muffler's noise elimination capability is very good ,but it has a very bad aerodynamic capability, you still can't use it. So when you are designing a muffler, you have to think about the noise elimination capability and the aerodynamic capability in the same time.Though the numerical simulation of three-dimensional flow in muffler, the three-dimensional distributing of the pressure and the velocity will be got. And the connection between the construction of the muffler and the flowing rule of the gas can be found. It can help us to design and improve the muffler. The numerical simulation of three-dimensional flow in muffler shold be done, then the condition of the air flow in the muffler and a way to improve the muffler can be got.The experiment platform was built according to the ?acoustics the measuring method of the muffler GB/T4760—1995?. The influence is caused by the air flow in the noise elimination and aerodynamic capability of the muffler.Though the experiment ,some results were got as follow:1 when the velocity of the air flow gets bigger, the insertion loss is getting smaller.2 when the velocity of the air flow gets bigger, the regeneration noise is getting bigger.3 when the velocity of the air flow gets bigger, the pressure loss is getting bigger.According to the condition of the experiment, the CFD simulation tool FIRE was used to simulate the three-dimensional flow in the muffler. Then the three-dimensional results as speed,pressure,turbulence energy were got. The results of the experiment and the results of the simulation show consistency. The results are when the velocity of the air flow is getting bigger,the turbulence energy,the regeneration noise and the pressure loss are getting smaller.The CFD software FIRE was used to simulate the improved model of the muffler, the velocity on the inlet of the muffler and a lot of three-D information were got. The software GT-Power was used to simulate the sound field of the muffler improved. Then the result of the improving was evaluated and the conclusions were got as follow:1 The diameter of the perforation is a important factor that infects the condition of the flow field in the muffler. When the diameter of the perforation gets much bigger, the turbulence energy,the regeneration noise and pressure loss are going to become much smaller.2 The inserting length of the tube is also a very important factor that infects the condition of the flow field in the muffler. In this paper the tube becomes 10 mm short. After the improving the local velocity is getting smaller, and the disturbing influence of the grads of the velocity and the direction is getting weaker. And the turbulence energy,the regeneration noise and pressure loss are also going to become much smaller.3 According to the result of the acoustic simulation, the change of the two factors make the noise elimination capability of the muffler much weaker. So the acoustic field and the flow field are both important for designing muffler.