Unsteady Aerodynamics and Blade-Row Interactions in the Embedded Stage of an Axial Compressor

In a mature engineering field like compressor aerodynamics, the most accessible advances in machine technology, translating to performance and efficiency, have been discovered and have found industry design applications. As the community continues to make progress, increasingly challenging aspects of the involved physics must be exploited. Modern turbomachinery operates with larger bypass ratios, smaller cores, and lighter, thinner, and more flexible materials resulting in the maintenance of higher operating pressures and temperatures. As the performance and efficiency of these machines continues to climb, the same technological advances reinforce challenges like forced-response vibration, high-cycle fatigue of engine components, and large relative tip clearances in an engine core. Accounting for these challenges increasingly depends on the investigation of the unsteady domain for solutions. Tools at the disposal of the designer include progressively improving computational simulations through both computational resources and attainable model fidelity. As essential as these tools are for modern turbomachinery design, the confidence in their results is only as good as the experimental data used to validate them. The objective of this research is the experimental investigation and characterization of the transient aerodynamics and blade-row interactions near forced-response resonant vibratory operating conditions in a multi-stage environment. Experimental methods are focused on fast-response pressure transducers with the high frequency response capable of capturing the unsteady pressure fluctuations associated with the high-speed rotation and blade-pass frequency of a modern high-pressure core axial compressor. Investigation is centered on an engine-representative embedded rear stage, with adjacent stages establishing realistic flow conditions and resulting boundary conditions for model comparison. Aerodynamic characterization of several flow conditions and the examination of the effect of a reduced vane-count stator configuration upstream of the embedded stage are performed with measurements of the embedded rotor at the casing endwall and rotor exit plane, as well as within a passage of the embedded stator. Circumferential vane traverse around stationary instrumentation provide a full vane passage of phase-locked, time-resolved pressure measurements of the rotor aerodynamics and the unsteady loading of the embedded stator is distinguished for a single vane position. Results from this investigation identify and describe the inception and trajectory of tip clearance flows, including the tip leakage vortex and double-leakage tip clearance flow. Evidence of an upstream vane wake interaction with the rotor occurs for limited regions of vane passage positions. Spectral analyses and pressure unsteadiness provide further insight into the blade-row interactions