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Full-Text Articles in Aerospace Engineering
Effect Of Thin Film Confined Between Two Dissimilar Solids On Interfacial Thermal Resistance, Zhi Liang, Hai-Lung Tsai
Effect Of Thin Film Confined Between Two Dissimilar Solids On Interfacial Thermal Resistance, Zhi Liang, Hai-Lung Tsai
Mechanical and Aerospace Engineering Faculty Research & Creative Works
A Non-Equilibrium Molecular Dynamics Model is Developed to Investigate How a Thin Film Confined between Two Dissimilar Solids Affects the Thermal Transport Across the Material Interface. for Two Highly Dissimilar (Phonon Frequency Mismatched) Solids, It is Found that the Insertion of a Thin Film between Them Can Greatly Enhance Thermal Transport Across the Material Interface by a Factor of 2.3 If the Thin Film Has One of the Following Characteristics: (1)a Multi-Atom-Thick Thin Film of Which the Phonon Density of States (DOS) Bridges the Two Different Phonon DOSs for the Solid on Each Side of the Thin Film; (2)a Single-Atom-Thick …
Direct Numerical Simulation Of Hypersonic Turbulent Boundary Layers. Part 4. Effect Of High Enthalpy, L. (Lian) Duan, M. P. Martín
Direct Numerical Simulation Of Hypersonic Turbulent Boundary Layers. Part 4. Effect Of High Enthalpy, L. (Lian) Duan, M. P. Martín
Mechanical and Aerospace Engineering Faculty Research & Creative Works
In this paper we present direct numerical simulations (DNS) of hypersonic turbulent boundary layers to study high-enthalpy effects. We study high-and low-enthalpy conditions, which are representative of those in hypersonic flight and ground-based facilities, respectively. We find that high-enthalpy boundary layers closely resemble those at low enthalpy. Many of the scaling relations for low-enthalpy flows, such as van-Driest transformation for the mean velocity, Morkovin's scaling, and the modified strong Reynolds analogy hold or can be generalized for high-enthalpy flows by removing the calorically perfect-gas assumption. We propose a generalized form of the modified Crocco relation, which relates the mean temperature …
Effective Approach For Estimating Turbulence-Chemistry Interaction In Hypersonic Turbulent Boundary Layers, L. (Lian) Duan, M. P. Martín
Effective Approach For Estimating Turbulence-Chemistry Interaction In Hypersonic Turbulent Boundary Layers, L. (Lian) Duan, M. P. Martín
Mechanical and Aerospace Engineering Faculty Research & Creative Works
An effective approach for estimating turbulence-chemistry interaction in hypersonic turbulent boundary layers is proposed, based on "laminar- chemistry" Reynolds-averaged Navier-Stokes mean flow solutions. The approach combines an assumed probability density function with a temperature fluctuation scaling, which provides the second moment for specifying the shape of the probability density function. As a result, the effects of temperature fluctuation on chemical production rates can be estimated without solving an additional moment evolution equation. The validity of this method is demonstrated using direct-numerical-simulation data. This approach can be used to identify regions with potentially significant turbulence-chemistry interaction in hypersonic boundary layers and …
Effect Of The Thickness Of Undoped Gan Interlayers Between Multiple Quantum Wells And The P-Doped Layer On The Performance Of Gan Light-Emitting Diodes, T. Lu, S. Li, K. Zhang, C. Liu, Y. Yin, L. Wu, H. Wang, Xiaodong Yang, G. Xiao, Y. Zhou
Effect Of The Thickness Of Undoped Gan Interlayers Between Multiple Quantum Wells And The P-Doped Layer On The Performance Of Gan Light-Emitting Diodes, T. Lu, S. Li, K. Zhang, C. Liu, Y. Yin, L. Wu, H. Wang, Xiaodong Yang, G. Xiao, Y. Zhou
Mechanical and Aerospace Engineering Faculty Research & Creative Works
InGaN based light-emitting diodes (LEDs) with undoped GaN interlayer of variant thicknesses grown by metal-organic chemical vapor deposition technique have been investigated. It was found that the thickness of undoped GaN interlayers affected LEDs' performance greatly. The LED with 50 nm undoped GaN interlayer showed higher light output power and lower reverse-leakage current compared with the others at 20 mA. Based on electrical and optical characteristics analysis and numerical simulation, these improvements are mainly attributed to the improvement of the quality of depletion region by inserting an undoped GaN layer, as well as reduction of the Shockley-Read-Hall recombination in InGaN/GaN …
Thermal Expansions In Wurtzite Aln, Gan, And Inn: First-Principle Phonon Calculations, L.-C. Xu, R.-Z. Wang, Xiaodong Yang, H. Yan
Thermal Expansions In Wurtzite Aln, Gan, And Inn: First-Principle Phonon Calculations, L.-C. Xu, R.-Z. Wang, Xiaodong Yang, H. Yan
Mechanical and Aerospace Engineering Faculty Research & Creative Works
Using the first-principle phonon calculations under the quasiharmonic approximation, thermal expansions in III-nitrides with wurtzite AlN, GaN, and InN are reported. The results showed that it is different for each thermal expansion of three III-nitrides at low temperatures, which is consistent with their Grneisen parameters as the function of temperature. Below 50 K, negative thermal expansions occur in InN, while GaN and AlN follow the rule of positive thermal expansion. To seek the origin of positivenegative thermal expansion distinction, the mode Grneisen parameters and the phonon spectra are investigated. They indicate that different low-frequency phonon vibration modes correspond to the …
Effect Of Molecular Film Thickness On Thermal Conduction Across Solid-Film Interfaces, Zhi Liang, Hai-Lung Tsai
Effect Of Molecular Film Thickness On Thermal Conduction Across Solid-Film Interfaces, Zhi Liang, Hai-Lung Tsai
Mechanical and Aerospace Engineering Faculty Research & Creative Works
The Brownian Motion and Aggregation of Particles in Nanofluids Often Lead to the Formation of Solid-Film-Solid Structures. the Molecular Thin Film Confined between Nanoparticles May Have Non-Negligible Effects on Thermal Conduction among Nanoparticles. using Nonequilibrium Molecular Dynamics Simulations, We Study Thermal Conduction Across the Ag Particle-Ar Thin-Film Interface. If the Film Contains Only One Molecular Layer, We Find that the Solid-Film Interfacial Thermal Resistance RSF is About 1 Order of Magnitude Smaller Than the Solid-Liquid (Bulk) Interfacial Thermal Resistance RSL. If There Are Two or More Molecular Layers in the Film, It is Shown that RSF Increases Rapidly toward RSL …
Direct Numerical Simulation Of Hypersonic Turbulent Boundary Layers. Part 3. Effect Of Mach Number, L. (Lian) Duan, I. Beekman, M. P. Martín
Direct Numerical Simulation Of Hypersonic Turbulent Boundary Layers. Part 3. Effect Of Mach Number, L. (Lian) Duan, I. Beekman, M. P. Martín
Mechanical and Aerospace Engineering Faculty Research & Creative Works
In this paper, we perform direct numerical simulations (DNS) of turbulent boundary layers with nominal free-stream Mach number ranging from 0.3 to 12. The main objective is to assess the scaling's with respect to the mean and turbulence behaviors as well as the possible breakdown of the weak compressibility hypothesis for turbulent boundary layers at high Mach numbers (M > 5). We find that many of the scaling relations, such as the van Driest transformation for mean velocity, Walz's relation, Morkovin's scaling and the strong Reynolds analogy, which are derived based on the weak compressibility hypothesis, remain valid for the range …
Thermal Conductivity Of Interfacial Layers In Nanofluids, Zhi Liang, Hai-Lung Tsai
Thermal Conductivity Of Interfacial Layers In Nanofluids, Zhi Liang, Hai-Lung Tsai
Mechanical and Aerospace Engineering Faculty Research & Creative Works
Thermal Conductivity of Interfacial Layers is an Essential Parameter for Determining How the Ordered Liquid Layering Around the Particle-Liquid Interface Contributes to the Unusual High Thermal Conductivity of Nanofluids. However, So Far There is No Experimental Data Regarding This Parameter. using Nonequilibrium Molecular Dynamics Simulations of an Inhomogeneous Au-Ar System in Which the Solid-Liquid Interactions Are Assumed to Be Much Stronger Than the Liquid-Liquid Interactions, We Show Explicitly that the Thermal Conductivity of a 1-Nm-Thick Interfacial Layer is 1.6∼2.5 Times Higher Than that of the Base Fluid. the Simulation Results Are Incorporated into a Three-Level Clustering Model to Calculate the …
Deterministic Integrated Tuning Of Multicavity Resonances And Phase For Slow-Light In Coupled Photonic Crystal Cavities, T. Gu, S. Kocaman, Xiaodong Yang, J. F. Mcmillan, M. B. Yu, G.-Q. Lo, D.-L. Kwong, C. W. Wong
Deterministic Integrated Tuning Of Multicavity Resonances And Phase For Slow-Light In Coupled Photonic Crystal Cavities, T. Gu, S. Kocaman, Xiaodong Yang, J. F. Mcmillan, M. B. Yu, G.-Q. Lo, D.-L. Kwong, C. W. Wong
Mechanical and Aerospace Engineering Faculty Research & Creative Works
We present the integrated chip-scale tuning of multiple photonic crystal cavities. The optimized implementation allows effective and precise tuning of multiple cavity resonances (up to ~1.60 nm/mW) and intercavity phase (~0.038 π/mW) by direct local temperature tuning on suspended silicon nanomembranes. Through designing the serpentine metal electrodes and careful electron-beam alignment to avoid cavity mode overlap, the coupled photonic crystal L3 cavities preserve their high quality factors. The deterministic resonance and phase control enables switching between the all-optical analog of electromagnetically-induced-transparency to flat-top filter lineshapes, with future applications of trapping photons and optoelectronic modulators.
Study Of Emission Turbulence-Radiation Interaction In Hypersonic Boundary Layers, L. (Lian) Duan, M. P. Martín, I. Sohn, D. A. Levin, M. F. Modest
Study Of Emission Turbulence-Radiation Interaction In Hypersonic Boundary Layers, L. (Lian) Duan, M. P. Martín, I. Sohn, D. A. Levin, M. F. Modest
Mechanical and Aerospace Engineering Faculty Research & Creative Works
Direct numerical simulations are conducted to study the effects of emission turbulence-radiation interaction in hypersonic turbulent boundary layers, representative of the Orion Crew Exploration Vehicle at peak-heating condition during reentry. A nondimensional governing parameter to measure the significance of emission turbulence-radiation interaction is proposed, and the direct numerical simulation fields with and without emission coupling are used to assess emission turbulence-radiation interaction. Both the uncoupled and coupled results show that there is no sizable interaction between turbulence and emission at the hypersonic environment under investigation. An explanation of why the intensity of emission turbulence-radiation interaction in the hypersonic boundary layer …
Assessment Of Turbulence-Chemistry Interaction In Hypersonic Turbulent Boundary Layers, L. (Lian) Duan, M. P. Martín
Assessment Of Turbulence-Chemistry Interaction In Hypersonic Turbulent Boundary Layers, L. (Lian) Duan, M. P. Martín
Mechanical and Aerospace Engineering Faculty Research & Creative Works
Studies of the turbulence-chemistry interaction are performed in hypersonic turbulent boundary layers using direct numerical simulation flow fields under typical hypersonic conditions representative of blunt-body and slender body hypersonic vehicles, with super catalytic and noncatalytic wall conditions in pure air. Nondimensional governing parameters, the interaction Damköhler number and the interaction relative heat release, are proposed to measure the influence of turbulence-chemistry interaction on flow composition and temperature. Both a priori and posteriori studies are performed to assess the effect of turbulence-chemistry interaction on chemical production rates and mean and turbulent flow characteristics. It is found that the governing parameters provide …
Study Of Turbulence-Chemistry Interaction In Hypersonic Turbulent Boundary Layers, Lian Duan, M. Pino Martín
Study Of Turbulence-Chemistry Interaction In Hypersonic Turbulent Boundary Layers, Lian Duan, M. Pino Martín
Mechanical and Aerospace Engineering Faculty Research & Creative Works
Studies of the turbulence-chemistry interaction (TCI) are performed in hypersonic turbulent boundary layers using direct numerical simulation (DNS) flow fields under typical hypersonic conditions representative of blunt-body and slender-body hypersonic vehicles, with super catalytic and noncatalytic wall conditions in pure air. Nondimensional governing parameters, 'interaction' Damk̈ohler number and relative heat release, are proposed to measure the influence of TCI on flow composition and temperature. Both a priori and posteriori studies are performed to assess the effect of TCI on chemical production rates and mean and turbulence flow characteristics. In addition, an effective approach (called PDF-TS) to estimate the intensity of …
Study Of Turbulence-Radiation Interaction In Hypersonic Turbulent Boundary Layers, L. (Lian) Duan, A. M. Feldick, M. P. Martín, M. F. Modest, D. A. Levin
Study Of Turbulence-Radiation Interaction In Hypersonic Turbulent Boundary Layers, L. (Lian) Duan, A. M. Feldick, M. P. Martín, M. F. Modest, D. A. Levin
Mechanical and Aerospace Engineering Faculty Research & Creative Works
In the paper, we conduct direct numerical simulations (DNS) to investigate the effect of turbulence-radiation interaction (TRI) in hypersonic turbulent boundary layers, representative of the Orion crew exploration vehicle (CEV) at peak heating condition during reentry. The radiative transfer equation (RTE) is solved using the tangent slab approximation. 1 The RTE solver is line-by-line (LBL) accurate, making use of a developed efficient spectral database 2 for spectral modeling. A multi-group full-spectrum correlated-k-distribution (FSCK) method 3 is used to reduce the number of RTE evaluations while preserving LBL accuracy. A nondimensional governing parameter to measure the significance of TRI is proposed, …