Calculation tool NoBel for sound propagation assessment of noise from gasturbines on the ground

Gas turbine engines of aviation type are the basic element of gas-pumping stations of the pipelines around in the world. They produce harmful noise and the protection zone around the gas-pumping station must provide the safe distance to residence in its vicinity. Due to Ukrainian legal requirements for the stationary (not movable) noise sources the sound pressure levels in octave bands must be used as limits for protection of the population complementarily to equivalent and maximum sound levels at day and night periods. A new calculation tool was designed to assess the effects during sound wave propagation from stationary noise sources like gas-turbine installations, as for homogeneous atmosphere, so as for real meteorological and topographical conditions. The tool provides the possibility to predict the conditions of maximum noise exposure at point of noise control. For homogeneous atmosphere the divergence, air absorption, ground surface reflection and acoustic screens contribute to propagation effects mostly. Their formulation in accordance with current knowledge provides more accurate sound levels assessment with differences ± 2 dBA at the boundaries of protection zone in comparison with existing national legal requirements of noise protection calculations. In real atmosphere temperature and wind (in direction and speed) vary with altitude over the ground surface always. These real conditions provide the dependence of sound speed with altitude, and in consequence the refraction of sound waves. For specific conditions of positive sound refraction the tool predicts the sound levels at the receiver up to 10 dBA higher, at negative sound refraction - on 5-7 less than in homogeneous atmosphere for legal protection distances. Tool NoBel is appropriate to be used for specific airport stationary noise scenarios, like for aircraft engine run-ups after their maintenance or repair.