The Experimental Investigation of a Rotor Icing Model with Shedding

Open Access
Author:
Brouwers, Edward William
Graduate Program:
Aerospace Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
None
Committee Members:
  • Dr Smith, Thesis Advisor
  • Edward Smith, Thesis Advisor
Keywords:
  • Rotorcraft
  • icing
  • Adverse Environment Rotor Test Stand
  • AERTS
  • LEWICE
  • shedding
  • ice accretion
  • impingment limits
  • torque degradation
Abstract:
A critical operational problem for rotorcraft is flight in adverse weather conditions. Flight in icing conditions is fraught with operational hazards, including reduced vehicle performance and degraded handling qualities. Additionally, shedding of ice from blades due to centrifugal force poses a ballistics danger to the aircraft and creates large vibrations due to imbalanced rotors. Modeling the effects of accreted ice on rotorcraft flight performance has been a challenge due to the complexities of periodically changing conditions as well as spanwise variations of angle of attack, velocities and surface temperatures. Model validation has been complicated by the lack of available data due to the existence of only a few facilities designed to study the rotorcraft aspect of the icing problem. As part of the development of the Adverse Environment Rotor Test Stand (AERTS), a new icing model was developed to predict ice shapes on a hovering rotor. The AERTS Rotor Icing, Shedding and Performance (ARISP) model has the goal of exploring rotor icing trends. The core feature of the model is the coupling with NASA’s LEWis ICE accretion code (LEWICE). Rotor performance is predicted with a blade element momentum theory module, while increases in rotor torque due to ice accretions are empirically calculated. A shedding module predicts the shedding time and blade station based upon the accreted ice properties. The ARISP model was correlated with published ice shapes for both small-scale and full-scale rotor ice accretion results. Further correlations were made with experiments in the newly developed Adverse Environment Rotor Test Stand (AERTS). These experiments constitute the first ice shape comparisons in the test stand. A total of 44 test cases were completed, of which the first 23 were designed to explore the limitations of the AERTS facility. The remaining 21 cases formed the test matrix for the ARISP model validation and were designed to investigate the influence of various icing parameters. Favorable comparisons have been made between ice shape, especially at inboard stations. Primary ice shape features were predicted well for over 81% of the experimental ice tracings. The largest discrepancies occurred at test cases that did not lie within the FAR Part 25/29 Appendix C icing envelope. Impingement limits were modeled well, with the discrepancies between the limit calculations and experimental values generally lower than 20%. Torque rise predications were generally within 20% of experimental values. Shedding behavior was also evaluated, but correction factors were required to improve test data correlation due to the general overprediction of tip ice accretions. These correction factors were derived from the difference in ice shape between predictions and experiments and reduced prediction error in shedding time to 25% and shedding station to 8%. Further investigations are required, but the icing model has laid the foundation for future research in the AERTS Facility.