Forcing function variability and its effect on airfoil response

Abstract

Aerodynamic variability effects on wake generated forcing functions and its impact on the downstream stator vane response are investigated in a high-speed 1&1/2 stage axial-flow turbomachine. The variability in the rotor wake generated gust components as well as the detailed vane surface pressure distributions ate quantified at both design and off-design rotor operating conditions. Wake generated forcing function variability is found to be significant even at the design rotor speed, with the vane response variability highest near the leading edge. At certain operating conditions a rogue wake is present in the rotor generated forcing function, with this wake not part of the Gaussian distribution describing the statistical variations of the flow field. The vane responded to this rogue wake only in the leading edge region. Blade-to-blade rotor wake variability introduces broadband energy into the forcing function spectrum, with the vane responding to these broadband components in addition to the blade pass frequency harmonics. At off-design operating conditions the broadband vane response due to wake variability was nearly half of the response occurring at blade pass frequency. NOMENCLATURE C Stator Vane Chord C Pressure Coefficient CL Unsteady Lift Coefficient f Frequency fBP Blade Pass Frequency Nc Corrected Rotor Speed p Static Pressure t Time TBP Blade Pass Period u, v* Streamwise and Transverse Gust Components V Absolute Velocity Magnitude a Absolute Flow Angle (cw) Ap Airfoil Unsteady Pressure Difference, pps pss 6igv IGV Stagger Angle p Density a Standard Deviation + Research Assistant, Student Member AIAA * McAllister Distinguished Professor, Associate Fellow AIAA Subscripts ave Time-Average ps Airfoil Pressure Surface ss Airfoil Suction Surface oo Freestream