Applicability of Low-Fidelity Tonal and Broadband Noise Models on Small-Scaled Rotors

Abstract

This paper presents the application of steady and unsteady frequency-domain propeller tonal noise and empirical helicopter broadband noise models for drone or small-scale rotor noise. These models provide a quick assessment of rotor noise, which is useful during the initial stages of aircraft design or optimization. Four frequency-domain tonal noise prediction models and three empirical broadband noise models are validated and compared using small rotor cases to analyze the predictive capabilities and limitations of these models. It is found that the steady frequency-domain models tend to over-predict the tonal noise at the fundamental blade passing frequency, and these models cannot capture noise along the rotor axis, thus resulting in a significant under-prediction near the rotor axis. This limitation is overcome by the unsteady frequency-domain model, but this model is limited to hover flight only. Moreover, the empirical broadband noise models show large over-predictions on a small rotor with a relatively higher thrust coefficient. Since these broadband noise models are not found to be robust, a more accurate model is needed to be developed for small rotor applications.