Flow Noises Associated with Integrated Compressor Anti-Surge Valve 2011-01-1532
Turbocharged gasoline engines are typically equipped with a compressor anti-surge valve or CBV (compressor by-pass valve). The purpose of this valve is to release pressurized air between the throttle and the compressor outlet during tip-out maneuvers. At normal operating conditions, the CBV is closed.
There are two major CBV mounting configurations. One is to mount the CBV on the AIS system. The other is to mount the CBV directly on the compressor housing, which is called an integrated CBV. For an integrated CBV, at normal operating conditions, it is closed and the enclosed passageway between high pressure side and low pressure side forms a “side-branch” in the compressor inlet side (Figure 12). The cavity modes associated with this “side-branch” could be excited by shear layer flow and result in narrow band flow noises. Depending on the side-branch geometry and the interactions between cavity-modes and shear layer excitations, this narrow band flow induced noise frequency could range from a few hundred hertz to a few thousand hertz.
Both CAE analysis and testing were conducted to understand this flow induced noise issues associated with the integrated CBV. CAE analysis can be used to calculate the resonant frequencies of “side-branch” cavity modes. Experimental testing, either on turbocharger flow rig, turbocharger gas stand, or Powertrain engine dyno, was also conducted to identify this phenomenon and verify CAE predicted frequencies. However, there is no currently available tool to accurately predict whether or not those cavity modes will be excited by shear layer flow excitations other than hardware testing.