An advanced casing treatment (CT) design was tested in a single-stage, high-speed axial compressor. The geometry of the casing included bent-axial slots applied near the rotor leading edge. Compressor performance and stall margin (SM) measurements were acquired for both casing treatment and for the smooth wall case at four different corrected speeds. The measurements also included rotor-exit radial traverses of unsteady total pressure. The results indicated an increase in rotor pressure ratio at all operating conditions with the application of the casing treatment. The stall margin also increased at all rotor speeds. Efficiency increases were observed with the casing treatment at design conditions and some off-design conditions. Numerical simulations of the IGV, rotor, and stator were conducted with and without the casing treatment. These results served to validate the efficacy of the part-wheel unsteady Reynolds-averaged Navier–Stokes (URANS) simulations to predict the effects of the casing treatment. The simulations also allowed a detailed study of the flow physics related to the interactions between the rotor and casing.

The relationship between aerodynamic forcing and non-synchronous vibration (NSV) in axial compressors remains difficult to ascertain from experimental measurements. In this work, the relationship between casing pressure and blade vibration was investigated using experimental observations from a 1.5-stage axial compressor under off-design conditions. The wavenumber-dependent auto-spectral density (ASD) of casing pressure was introduced to aid in understanding the characteristics of pressure fluctuations that lead to the aeromechanical response. Specifically, the rotor blade’s natural frequencies and nodal diameters could be directly compared with the pressure spectra. This analysis indicated that the rotating disturbances coincided with the first bending (1B) and second bending (2B) vibration modes at certain frequencies and wavenumbers. The non-intrusive stress measurement system (NSMS) data showed elevated vibration amplitudes for the coincident nodal diameters. The amplitude of the wavenumber-dependent pressure spectra was projected onto the single-degree-of-freedom (SDOF) transfer function and was compared with the measured vibration amplitude. The results showed a near-linear relationship between the pressure and vibration data.

Nonsynchronous vibration (NSV) in axial compressors can be caused either by (1) unsteady aerodynamic forces that are not related to motion of the blades or (2) motion-dependent aerodynamic forcing (e.g., flutter). Aerodynamic forcing mechanisms can be challenging to identify in experimental observations of NSV because the temporal vibration characteristics for both forcing mechanisms can appear similar. This work proposes a method for distinguishing between the two mechanisms using spectral characteristics. The method provides an interpretation of experimental data explicitly consistent with the analytical models used to differentiate between forced response and flutter. Two cases of NSV were observed in a 1.5-stage axial compressor at near-stall conditions. The circumferential wavenumber-dependent unsteady pressure spectra and nonintrusive stress measurement system (NSMS) spectra were observed to have distinct characteristics for the two NSV cases. Based on these distinct spectral characteristics, the first case was identified as blade-row aerodynamic forcing, while the second was identified as motion-dependent (flutter). Numerical simulations confirmed low aerodynamic damping at the conditions where flutter was observed.

Quasi-direct current (Q-DC) filamentary electrical discharges are used to control the shock train in a back-pressured Mach 2 duct flow. The coupled interaction between the plasma filaments and the shock train leading edge (STLE) is studied for a variety of boundary conditions. Electrical parameters associated with the discharge are recorded during actuation, demonstrating a close correlation between the STLE position and dynamics. High-speed self-aligned focusing schlieren (SAFS) and high frame-rate color camera imaging are the primary optical diagnostics used to study the flowfield and plasma morphology. Shock tracking and plasma characterization algorithms are employed to extract time-resolved quantitative data during shock–plasma interactions. Four distinct shock–plasma interaction types are identified and outlined, revealing a strong dependence on the spacing between the uncontrolled STLE and discharge electrodes and a moderate dependence on flow parameters.

The study of entropy in the context of quasi-one-dimensional flow is expanded in this work. Specifically, a new entropy transport equation is derived and integrated into a closed-form algebraic expression for entropy change. The derivation identifies the respective components of the entropy change and is valid for flows with an arbitrary combination of area change, heat transfer, and friction. The irreversibility is identified and found to be composed of frictional dissipation, irreversible heat transfer, and irreversible flow work. The irreversible flow work is a new term that results from the restriction to quasi-one-dimensional flows. The algebraic expression for each component of the entropy change is first validated using several canonical flows (i.e., isentropic, Fanno, Rayleigh, and a normal shock). A unique entropy production mechanism is identified for each of the entropy producing canonical flows (e.g., Fanno, Rayleigh, and a normal shock). Two additional cases, sudden expansion and contraction, are then considered and show that irreversible flow work is the sole entropy production mechanism. Finally, simultaneous friction and heat transfer are examined, and the overall entropy change is decomposed into the respective contributions from frictional dissipation and the heat transfer terms. In all cases, the net entropy change from the newly derived expressions agrees with known solutions to within numerical precision.

A transonic annulus turbine cascade facility was built at Notre Dame Turbomachinery Laboratory to study flutter phenomena of transonic cooled turbine blade. Three center blades with modern cooled 3-dimensional aero design were instrumented with 144 EA of ultraminiature fast-response pressure transducers on the blade surface at 50%, 75%, and 95% of blade spans. Center blade and