Control of discrete-frequency turbomachine noise using active and passive techniques
Abstract
Turbomachine discrete-frequency tones, a significant environmental concern, are generated by rotor-stator interactions. Specific spatial modes are generated by rotor-stator interactions. However, only certain of these modes propagate to the far-field. Thus, the propagating spatial modes represent the community disturbing far-field discrete-frequency noise. A series of fundamental experiments demonstrated the viability and effectiveness of active and passive discrete-frequency noise control techniques. Passive discrete-frequency noise control was accomplished through rotor detuning. The effectiveness of this technique was determined using the overall intensity level. The detuned rotor was described by a two cycle sinusoidal variation in the angular blade spacing. This clustered the blades at opposite sides of the rotor and retained the rotor balance. Rotor detuning was determined to consistently reduce the overall intensity level by approximately 6 dB when the primary spatial mode generated by the rotor-stator interaction was cut-on at blade pass frequency. Active airfoil source control was optimized to generate propagating spatial modes to interact with and simultaneously cancel the upstream and downstream propagating spatial modes generated by the rotor-stator interactions. The active noise control system incorporated the active airfoil source control with in-duct spatial mode measurement. In this unique design. the active airfoils of the stator vane row were driven by a remote centerbody-mounted acoustic source. Two systems were utilized. The purpose of the first system was twofold. Using a system of compression drivers, this system achieved simultaneous upstream and downstream control of a propagating spatial mode. Significant control authority was exhibited over the entire range of operating conditions, with a simultaneous reduction of up to 20 dB upstream and downstream. The magnitude of the acoustic response and the required control signals were predicted using the linearized unsteady flow solver LINFLO. The compression driver system also demonstrated the simultaneous generation of two spatial modes propagating at blade pass frequency. This was a necessary step for the simultaneous control of a rotor-stator and a rotor-strut interaction. Finally, a rotory valve system demonstrated a 10 dB reduction of the propagating spatial mode generated by the rotor-stator interaction.
Degree
Ph.D.
Advisors
Fleeter, Purdue University.
Subject Area
Mechanical engineering
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