Achieving a high electrical conductivity while maintaining a good thermal insulation is often contradictory in the material design for the goal of simultaneous thermal protection and electromagnetic interference shielding. The reason is that materials with a high electrical conductivity often pertain a high thermal conductivity. To address this challenge, this study reports a multifunctional ceramic composite system for carbon fiberreinforced polymer composites. The fabricated multifunctional ceramic composite system has a multilayer structure. The polymerderived SiCN ceramic reinforced with yttria-stabilized zirconia fibers serves as the thermal protection and impedance-matching layer, while the yttria-stabilized zirconia fiber-reinforced SiCN ceramic with carbon nanotubes provides the electromagnetic interference shielding. The thermal conductance of the multilayered ceramic composite is about 22.5% lower compared to that of the carbon fiber-reinforced polymer composites. The thermal insulation test during the steady-state condition shows that the hybrid composite can be used up to 300 °C while keeping the temperature reaching the surface of carbon fiber-reinforced polymer composites at around 167.8 °C. The flame test was used to characterize the thermal protection capability under transient conditions. The hybrid composite showed temperature differences of 72.9 and 280.7 °C during the low-and high-temperature settings, respectively. The average total shielding efficiency per thickness of the fabricated four-layered ceramic composite system was 21.45 dB/mm, which showed a high reflection-dominant electromagnetic interference shielding. The average total shielding efficiency per thickness of the eight-layered composite system was 16.57 dB/mm, revealing a high absorption-dominant electromagnetic interference shielding. Typical carbon fiber-reinforced polymer composites reveal a reflection-dominant electromagnetic interference shielding. The electrons can freely move in the percolated carbon nanotubes within the inner layers of the composite material, which provide the improved electromagnetic interference shielding ability. The movement of electrons was impeded by the top and bottom layers whose thermal conduction relies on the lattice vibrations, resulting in a satisfactory thermal insulation of the composite materials and impedance matching with the free space. Results of this study showed that materials with a good thermal insulation and electromagnetic interference shielding can be obtained simultaneously by confining the electron movement inside the materials and refraining their movement at the skin surface.

This article contains an investigation of the unsteady acoustic forcing on a centrifugal impeller due to coupled blade row interactions. Selected results from an aeromechanical test campaign on a GE Oil and Gas centrifugal compressor stage with a vaneless diffuser are presented. The most commonly encountered sources of impeller excitation due to upstream wake interaction were identified and observed in the testing campaign. A 30/rev excitation corresponding to the sum of upstream and downstream vane counts caused significant trailing edge vibratory stress amplitudes. Due to the large spacing between the impeller and the return channel vanes, this 30/rev excitation was suspected to be caused by an aero-acoustic excitation rather than a potential disturbance. The origin of this aero-acoustic excitation was deduced from an acoustic analysis of the unsteady compressor flow derived from CFD. The analysis revealed a complex excitation mechanism caused by impeller interaction with the upstream vane row wakes and subsequent acoustic wave reflection from the downstream return channel vanes. The findings show it is important to account for aero-acoustic forcing in the aeromechanical design of low pressure ratio centrifugal compressor stages.

Building upon the successes of the UDF® program in the 1980’s, open rotor designs for high flight speed efficiency and low community noise have been developed at GE in collaboration with NASA and the FAA. Targeting a narrow body aircraft with 0.78 cruise Mach number, the cost-share program leveraged computational fluid dynamics (CFD), computational aero-acoustics (CAA), and rig scale testing to generate designs that achieved significant noise reductions well beyond what was attained in the 1980’s while substantially retaining cruise performance. This paper presents overall propeller net efficiency and acoustic assessments of GE’s modern open rotor designs based on measured rig data and the progression of the technology from the 1980’s through the present. Also discussed are the effects of aft rotor clipping, inter-rotor spacing, and disk loading. This paper shows how the two-phase design and scale model wind tunnel test program allowed for test results of the first design phase to feed back into the second design phase, resulting in 2–3% improvement in overall propeller net efficiency than the best efficiency design of the 1980’s while nominally achieving 15–17 EPNdB noise margin to Chapter 4 (when projected to full scale for a prescribed aircraft trajectory and installation). Accounting for trades and near term advancements, such a propulsion system is projected to meet the goal of 26% fuel burn reduction relative to CFM56-7B powered narrow body aircraft.

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