Wind Turbine Aerodynamics - 11 - Noise Immission

24 August 2026, Cordula Hornung

Propagation

• With distance the sound pressure level redues due to spherical spreading
• doubling the distance corresponds to a loss of 6 dB

$$ \Delta = 20 log_{10}(\frac{r2}{r1}) $$

Atmospheric attenuation

• sound is attenuated by viscosity - converts sound energy into heat
• higher frequencies are damped significantly
• damping at lower frequencies almost negligable
• depends on humidity and temperature of air

Refraction

• bending of sound waves due to changes in propagation speed
• sound rays bend towards region with lower propagation speed
• depends on wind speed and temperature

Physics and Methods

• Many methods possible (linearized eouler equations, particle methods, raymethods, ...)
• all of those method are not applicable to wind farms, because they are too compuational expensive
• Solution: ISO 9613-2: attenuation of sound propagation outdoor
  • step 1: equivalent continous sound pressure level for each octave band
  • step 2: calculation of overall sound pressure level
  • step 3: consideration of influence of meterological effects on long term average

Regulations and Standards

• reference value (TA Lärm 6.1)
  • classification according to table
  • mixed areas possible
• impacted area / irrelevance criteria (TA Lärm 2.2)
  • area in which a turbine is significant for an immission point
  • difference between ferderal states and even regional authorities
• 1 dB criteria (TA Lärm 3.2.1)
  • in case of existing noise sources the reference value can be increased by 1 dB
• uncertainties are added to $L_{WA}: \sigma:{ges} = \sqrt{\sigma_R^2+\sigma_P^2+\sigma_{Prog}^2}$
  • $\sigma_R$: standard deviation of measurements
  • $\sigma_P$: standard deviation due to serial scattering
  • $\sigma_{Prog}$: standard deviation of the propagation mode

Interimprocedure

the interimprocedure describes the german handling of the ISO 9613-2 for wind turbines

• wind turbines have to be considered as one omnidirectional point source
• ground reflection terms are assumed to be invalid, because of large height of turbine

Wind Park Optimization

Needed: planned and existing wind park coordinates, relevant immission points, additional sound sources. Sound power levels for a range of modes. Reference values for sound immission. Maps and areal pictures.

Potential future possibilities (require change of legal regulations in germany)

• directivity of turbine
• directivity of propagation (wind direction depending)
• real time noise control by considering changes in emission and propagation depending on atmospheric conditions