Thermosetting epoxy (EP)-based composites containing various carbon nanofiber (CNF) contents (0-5 wt %) were fabricated using high speed mechanical stirring and surfactant assisting method. Then EP/CNF composites were foamed through a supercritical CO 2 (scCO 2 ) foaming method. The cellular morphology of the foamed EP/CNF nanocomposites has been analyzed by scanning electron microscopy (SEM), and the results demonstrated that the CNFs could be served as heterogeneous nucleating agent to increase nucleation sites in nanocomposites, leading to higher cell density and larger cell size. The influences of foaming on conductivity and electromagnetic interference (EMI) shielding effectiveness (SE) were investigated. Due to the introduction of microcellular structure, the conductivity was improved from 9.53 × 10 −8 S/cm to 6.75 × 10 −6 S/cm and the EMI SE was enhanced from 12.7 to 16.5 dB at the CNF content of 5 wt %.
Axial slot CTs were designed and applied on Rotor 67 to understand the physical mechanisms responsible for the improvement of the stall margin. Unsteady Reynolds-averaged Navier-Stokes was applied in addition to steady Reynolds-averaged Navier-Stokes to simulate the flow field of the rotor. The results show that aerodynamic performance and the rotor stability were improved. Stall margin improvement (SMI) improved by 26.85% after the CT covering 50% of the axial tip chord was applied, whereas peak efficiency (PE) decreased the least. The main reason for the rotor stall in the solid casing is the blockage caused by tip leakage flow. After axial slot CTs were applied, the tip leakage flow in the front part of the chord was obviously reduced, and the majority of the blockages in the tip region were removed. The absolute value of the axial momentum before 45% axial chord in CT_50 was reduced by 50%, whereas the maximum tangential momentum value of CT_50 was decreased by 70% relative to the solid casing. CT_50 configuration was located across the shock wave; thus, it can fully utilize the pressure gradient to bleed and remove the blockage region, and the across flow is considerably depressed.
Accurate prediction of the flow around multi-element airfoil is a prerequisite for improving aerodynamic performance, but its complex flow features impose high demands on turbulence modeling. In this work, delayed detached-eddy-simulation (DDES) and zonal detached-eddy-simulation (ZDES) was applied to simulate the flow past a three-element airfoil. To investigate the effects of numerical dissipation of spatial schemes, the third-order MUSCL and the fifth-order interpolation based on modified Roe scheme were implemented. From the comparisons between the calculations and the available experimental result, third-order MUSCL-Roe can provide satisfactory mean velocity profiles, but the excessive dissipation suppresses the velocity fluctuations level and eliminates the small-scale structures; DDES cannot reproduce the separation near the trailing edge of the flap which lead to the discrepancy in mean pressure coefficients, while ZDES result has better tally with the experiment.
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