Gas Turbine Handbook : Principles and Practices

Gas Turbine Acoustics and Noise Control 147
the duct system must be considered as that affects performance too.
Typically, a series of iterations are performed before arriving at “one”
potential solution. Then the entire system design must be reevaluated
to ensure meeting any other performance requirements such as
allowable system pressure loss or drop. Thus, this chapter is limited
to the principal elements of noise control that need to be considered
in the design process and is not intended as a solution manual.
NOISE SOURCES
There are three major sources of noise that contribute to the
combustion turbine’s noise emissions; they are casing, inlet and exhaust
emissions. The casing emission is the noise radiation from the
body of the turbine itself and through its ancillary equipment, piping,
and foundation. In most instances the turbine is in an enclosure or
inside a building that greatly reduces this source of noise. The inlet
and exhaust noises are principally aerodynamic sources. The inlet, or
compressor section, generally produces high frequency tones generated
by the blade passing frequency (bpf) and typically has several
harmonics as illustrated in Figure 10-1.
The fundamental bpf is calculated by counting the number of
inlet compressor blades and multiply by the turbine’s rotating speed.
Figure 10-1. Spectrum of a Turbine Inlet Tone and Harmonics