REDUCTION OF DISCRETE BLADE RATE TONES VIA SLOWLY ROTATING STATOR

Open Access
Author:
Auman, Kerstyn M
Area of Honors:
Aerospace Engineering
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • James Lindau, Thesis Supervisor
  • Mark Maughmer, Honors Advisor
Keywords:
  • Blade rate tone reduction
  • stator rotor interaction
  • discrete tone
  • blade passing frequency
  • autospectrum
  • decibel
  • unsteady force
  • relative velocity
Abstract:
Noise reduction is important in both commercial and military turbomachines. This thesis investigates the reduction of discrete tones produced by an upstream stator interacting with a rotor in a single stage by slowly rotating the stator. This method was investigated both computationally and experimentally for a co-rotating and counter-rotating stator rotating at some small fraction of the rotor rpm. Theoretical calculations were conducted in MATLAB using the Unsteady Forces and Moments (UFAM) script which predicts the unsteady forces and moments on a rotor due to an unsteady upstream stator gust by means of the Sears function and 2D strip theory. UFAM calculates the unsteady forces acting on the rotor due to a stationary upstream stator; modifications to the code were made in order to calculate the forces acting on the rotor due to a rotating stator. This was done by re-calculating the relative velocity into the rear rotor using velocity triangles. These calculations predict a co-rotating stator to decrease blade rate tones and for a counter-rotating stator to increase blade rate tones, depending upon the stator rpm. Typically, a stator rpm greater than 10% of the rotor rpm would lead to increases in the blade rate tones regardless of the direction of rotation. An experiment was designed in order to validate these results. The experiment consisted of a ducted single turbomachinery stage with an upstream cruciform. A microphone downstream of the end of the duct measured the noise produced for different co-rotating and counter-rotating stator configurations. Measurements were made in an anechoic chamber to reduce background noise effects. The experimental results displayed the same trend as predicted by the theory; validating that slowly co-rotating an upstream stator reduces blade rate tones.