The Omitted Noise Contribution of Surface Normal Variation: Farassat's Formulation 1A revisited
Abstract
Farassat's Formulations 1 and 1A have been extensively employed for propeller noise prediction. However, in the derivation of Formulation 1A from Formulation 1, the contribution associated with the temporal variation of the direction of the unsteady force is omitted, appearing mathematically as the temporal derivative of the local surface normal vector. Through rigorous mathematical derivation, this study demonstrates that the omitted term constitutes an indispensable component of the acoustic source representation. Accordingly, a Modified Formulation 1A is proposed by explicitly retaining the normal vector temporal derivative term in the time-domain formulation. Far-field acoustic predictions for propellers are performed to evaluate the proposed formulation, and the results confirm both its theoretical consistency and predictive capability.
Versions
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BibTeX
@misc{tao2026omitted,
title = {{The Omitted Noise Contribution of Surface Normal Variation: Farassat's Formulation 1A revisited}},
author = {Qitian Tao and Chen He and Xiaohua Liu and Zhengwu Chen and Jiale Lu},
howpublished = {arXiv},
year = {2026},
month = jun,
doi = {10.48550/arxiv.2606.07081},
eprint = {2606.07081},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2606.07081},
}
RIS
TY - UNPB
TI - The Omitted Noise Contribution of Surface Normal Variation: Farassat's Formulation 1A revisited
AU - Qitian Tao
AU - Chen He
AU - Xiaohua Liu
AU - Zhengwu Chen
AU - Jiale Lu
PY - 2026
DA - 2026/06/05
PB - arXiv
DO - 10.48550/arxiv.2606.07081
UR - https://arxiv.org/abs/2606.07081
AB - Farassat's Formulations 1 and 1A have been extensively employed for propeller noise prediction. However, in the derivation of Formulation 1A from Formulation 1, the contribution associated with the temporal variation of the direction of the unsteady force is omitted, appearing mathematically as the temporal derivative of the local surface normal vector. Through rigorous mathematical derivation, this study demonstrates that the omitted term constitutes an indispensable component of the acoustic source representation. Accordingly, a Modified Formulation 1A is proposed by explicitly retaining the normal vector temporal derivative term in the time-domain formulation. Far-field acoustic predictions for propellers are performed to evaluate the proposed formulation, and the results confirm both its theoretical consistency and predictive capability.
ER -