Showing papers by "Yueming Li published in 2018"

Experimental Characterization of the Thermal Conductivity and Microstructure of Opacifier-Fiber-Aerogel Composite.

Abstract: Due to their high-porosity, nanoporous structure and pores, aerogel materials possess extremely low thermal conductivity and have broad potential in the thermal insulation field Silica aerogel materials are widely used because of their low thermal conductivity and high temperature resistance Pure silica aerogel is very fragile and nearly transparent to the infrared spectrum within 3⁻8 μm Doping fibers and opacifiers can overcome these drawbacks In this paper, the influences of opacifier type and content on the thermal conductivity of silica fiber mat-aerogel composite are experimentally studied using the transient plane source method The thermal insulation performances are compared from 100 to 750 °C at constant pressure in nitrogen atmosphere among pure fiber mat, fiber mat-aerogel, 20% SiC-fiber mat-aerogel, 30% ZrO₂-fiber mat-aerogel and 20% SiC + 30% ZrO₂-fiber mat-aerogel Fiber mat-aerogel doped with 20% SiC has the lowest thermal conductivity, 00792 W/m·K at 750 °C, which proves that the proper type and moderate content of opacifier dominates the low thermal conductivity The pore size distribution indicates that the volume fraction of the micropore and mesopore is also the key factor for reducing the thermal conductivity of porous materials

The Lamb wave bandgap variation of a locally resonant phononic crystal subjected to thermal deformation

Abstract: A study on dynamical characteristics of a ternary locally resonant phononic crystal (PC) plate (i.e., hard scatterer with soft coating periodically disperse in stiff host matrix) is carried out in this paper. The effect of thermal deformation on the structure stiffness, which plays an important role in the PC’s dynamical characteristics, is considered. Results show that both the start and the stop frequency of bandgap shift to higher range with the thermal deformation. In particular, the characteristics of band structure change suddenly at critical buckling temperature. The effect of thermal deformation could be utilized for tuning of phononic band structures, which can promote their design and further applications.

Oxidation Simulation of Thermal Barrier Coatings with Actual Microstructures Considering Strength Difference Property and Creep-Plastic Behavior

Abstract: A scanning electron microscope (SEM) image based direct finite element (FE) mesh reconstruction method is employed to reflect microstructure features of thermal barrier coatings (TBC). The creep-plastic assumption of thermally grown oxide (TGO) scale and metallic bond coat (BC) as well as the strength difference (SD) property of ceramic top coat (TC) are considered to simulate the mechanical behavior. A diffusion oxidation model considering oxygen consumption is proposed to characterize TGO growth. The oxidation simulation of TBC is carried out under the consideration of actual microstructure features. The results revealed that the interface defects increase the surface-area-to-volume ratio of BC exposed to oxygen anion. This leads to the non-uniform TGO growth, which has also been observed in experimental studies. The microstructures and mechanical behavior strongly affect stress evolution in TBC. The consideration of actual microstructure features and reasonable mechanical behaviors, including the creep-plastic behavior and SD property, is helpful for the accurate evaluation of interface stress.

Computational-Fluid-Dynamics-Based Aeroservoelastic Analysis for Gust Load Alleviation

Abstract: Gust load alleviation using computational fluid dynamics as source of the aerodynamic predictions is carried out in the time domain. To this goal, an aeroservoelastic reduced-order model is generat...

Thermal stress effects on the flexural wave bandgap of a two-dimensional locally resonant acoustic metamaterial

Abstract: The elastic wave bandgap is obviously affected by heat while considering thermal stress. Nevertheless, the flat band, occurring in the lowest flexural branch, has not yet been explained clearly. This study investigates the influence of thermal stress on a flexural wave bandgap in a two-dimensional three-component acoustic metamaterial. Simulation results demonstrate that the band structure shifts to a lower frequency range, and the vibration response appears at a larger amplitude due to the bending stiffness being softened by the compressive membrane force. In addition, the first flexural band reduces to zero frequency in the central Brillouin zone. By viewing the vibration modes of the proposed unit cell, it is found that the out-of-plane mode shape attenuates with increasing temperature, while the in-plane vibration modes are unaffected by thermal stress.

Further Investigation on the Flow and Heat Transfer Mechanism of Single-Jet Film Cooling Based on Hybrid Thermal Lattice Boltzmann Method

Abstract: Massively parallel simulation applied multiple graphic processing units (multi-GPUs) is carried out to perform an in-depth investigation on the flow and heat transfer mechanism in film cooling based on hybrid thermal lattice Boltzmann method (HTLBM). For the flow field, multiple-relaxation-time (MRT) collision model is used. A coolant jet is injected at an inclined angle of α=30◦ into a turbulent flat plate boundary layer profile with free-stream Reynolds number of Re = 4000. In our previous work [1], we proposed a three-part definition for the jet-crossflow-interaction region according to the turbulent kinetic energy (TKE) distribution and the unsteady mixing characteristics in each domain were studied qualitatively. In order to further investigate this phenomenon, a more detailed study on unsteady flow and heat transfer characteristics is performed in this work. The results show that the shear domain is dominated by the shearing effect and covered by stable coolant film. In rotating domain, the turbulent intensity increases because of the violent mixing between crossflow and jet flow and the coolant film begins to spread in lateral. All of these cause the rapid decrease in coolant film stability. The great turbulent-dissipation effect in dissipation domain weakens the turbulent intensity and strengthens the fluctuation of spanwise velocity. The cooling performance is very poor. AMS subject classifications: 76F65

Vibro-acoustic characteristics of laminated plates with thermal buckling effect

Abstract: Vibration and acoustic radiation responses are investigated for pre and post-buckled laminated plates in thermal environments. Pre-stress effect induced by temperature variations of the plate was taken into account to describe the force and moment distribution during dynamic processes. Governing equations of the heated laminated composite plate were derived based on the firstorder shear deformation theory and von Karman nonlinear strain-displacement relation. Semianalytical solutions of vibro-acoustic responses were obtained for fully clamped rectangular plates in both pre and post-buckling temperature regions. Results showed that thermal loads reduce the stiffness of the laminated plate in the temperature range below the critical buckling value, and enhance the stiffness of the plate as thermal buckling occurs. Responses of vibration and radiated sound present a two-stage variation process, shifting toward the lower frequency range before thermal buckling and closing up in higher frequency band after the laminated plate buckles. Thermal environment preforms opposite effects before and after the critical buckling point. Theoretical results showed same variation trends with experimental results, and match with the numerical results as well.