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US Army Corps of Engineers - Marine Station

Title: The Helicopter Observation Platform: Demonstration and Calibration Phase

NSF Grant ID: 0623182; PI: R Avissar; Period: 01/01/07-12/31/08

USACE Duck To complete the development phase of the HOP, the goals of this project were (1) to calibrate the sensors and to decipher (and if needed filter) vibration signatures in the collected data, and (2) to study in details the aerodynamic envelope of the HOP using a combination of computational fluid dynamic (CFD) software and the calibrated sensors in flight. The ultimate goal of the latter was to assess the “operating range” of airspeeds for research missions. For this purpose, we performed a few flights at the Outer Banks of North Carolina, at airspeeds varying from 10 to 50 m/s. It appears that the only vibration detectable in the collected data is well correlated with the frequency of the main rotor at 13.1 – 13.4 Hz. Therefore, it can be easily filtered out of the data and, furthermore, it has only a minor impact on the fluxes calculated from the sensors outputs. It also appears that at airspeeds between 15 m/s and 45 m/s, no perturbation from the platform can be identified in the collected data (except for the above-mentioned vibration). As the airspeed drops below 15 m/s, a gradually more significant impact of the main rotor is noticed. Above 45 m/s, the aerodynamical perturbation generated by the helicopter frame also affects the air where the sensors are currently located. While this leaves a comfortable operating range for observations with a recommended operational airspeed of 30 m/s, these perturbations are explored with Fluent, the CFD that was adopted for this study.

USACE

Additional flights will be performed as needed to confirm the CFD results. These results are thoroughly described in Avissar et al (2008), Holder and Avissar (2008) and Holder et al (2008).

References

  • Avissar, R., H. E. Holder, P. Canning, K. Prince, N. Matayoshi, R. L. Walko, and K. M. Johnson, 2008. The Duke University Helicopter Observation Platform. Bulletin of the American Meteorological Society (submitted).
  • Holder, H.E. and R. Avissar, 2008. Measurements of turbulent fluxes in the atmospheric boundary layer with the Duke University Helicopter Observation Platform. J. Atmos. Ocean. Tech., in preparation.
  • Holder, H.E., K. Novick, D. Lenschow, N. Patton, W. Eichinger, N. Matayoshi and R. Avissar, 2008. An evaluation study of the turbulent fluxes measured on board the Duke University Helicopter Observation Platform. J. Atmos. Ocean. Tech., in preparation.