Search

Your search keyword '"Jiang, Hongyi"' showing total 282 results
Start Over Author "Jiang, Hongyi" Language english
282 results on '"Jiang, Hongyi"'

38. Direct numerical simulation of the turbulence characteristics in a cylinder wake

Author

Jiang, Hongyi, speaker

Abstract

The primary vortex street, turbulent kinetic energy and energy dissipation rate in the wake of a circular cylinder are examined at a Reynolds number of 1000 and up to 120 cylinder diameters downstream of the cylinder. The turbulence characteristics are quantified using direct numerical simulation (based on the framework of Nektar++), which provides a comprehensive dataset that is almost impossible to acquire from physical experiments. The energy dissipation rate is decomposed into the components due to the mean flow, the coherent primary vortices and the remainder. It is found that the remainder component, which develops only in a three-dimensional turbulent wake, accounts for the majority of the total dissipation rate for almost the entire wake. The turbulence dissipation in the wake is largely locally homogeneous, but not locally isotropic or axisymmetric, even after the annihilation of the primary vortex street. The spatial distribution of the turbulence characteristics relative to the spatial distribution of the primary and streamwise vortices is also examined.

Published
2022
Full Text
View/download PDF

49. On the absence of a secondary vortex street in three-dimensional and turbulent cylinder wakes.

Author

Jiang, Hongyi

Subjects
REYNOLDS number, TRANSIENT analysis, VORTEX motion, TURBULENCE, COMPUTER simulation
Abstract

Bluff-body wakes generally become three-dimensional (3-D) and then turbulent when the Reynolds number exceeds a few hundred. Other than an alternate shedding of the spanwise vortices behind the body and a gradual decay and annihilation of the vortices with distance downstream, whether a secondary vortex street would develop in the relatively far wake has been a long-standing argument in the literature. This argument is addressed in the present study. Specifically, direct numerical simulations and transient growth analysis are performed to examine the two-dimensional and 3-D wakes of different bluff bodies, including circular cylinder, square cylinder, diamond cylinder and rectangular cylinders with different cross-sectional aspect ratios. We found that a secondary vortex street is absent for most 3-D and turbulent wakes. The root cause is the weakening of spanwise vortices by 3-D wake instability modes and streamwise circulation/vorticity. The weakened spanwise vortices induce reduced mean shear in the intermediate wake, which then induces much smaller perturbation energy growth that is below the threshold for the emergence of a secondary vortex street. This finding suggests that the 3-D and turbulence characteristics, and the momentum, mass and heat transport in the relatively far wake of bluff bodies, would not be influenced by extra anisotropy or inhomogeneity caused by a secondary vortex street. [ABSTRACT FROM AUTHOR]

Published
2024
Full Text
View/download PDF

50. Preparation of High-Temperature Resistant Aerogels by Incorporating Aluminum Sol into Composite Silica Sources Using Ambient Pressure Drying.

Author

Gao, Shuai, Cao, Zeqi, Liu, Kai, Liu, Shuning, Pang, Wanjun, and Jiang, Hongyi

Subjects
PHASE transitions, AEROGELS, SOL-gel processes, INDUSTRIAL costs, SURFACE area
Abstract

To reduce production costs and enhance the high-temperature resistance of SiO2 aerogels, an aluminum-doped silica aerogel (ASA) was successfully prepared using the sol-gel method and atmospheric drying method. The composite silica sources included TEOS and inexpensive acidic silica sol, while the aluminum source was aluminum sol. The study investigated the influence of the molar ratio of acidic silica sol to TEOS, Al/Si, and calcination temperature on the composition, structure, and high-temperature resistance of the ASA. The results indicate that a sample with an acidic silica sol to TEOS molar ratio of 0.8 achieved a specific surface area of 683.204 m2·g−1. The Al/Si molar ratio significantly impacted the high-temperature resistance of the ASA, with the sample having a molar ratio of 0.02 Al/Si displaying the highest specific surface area of 705.956 m2·g−1 at 600 °C. Moreover, this surface area remained at 273.099 m2·g−1 after calcination at 1000 °C, notably higher than the sample without aluminum sol (16.082 m2·g−1). Mechanism analysis indicated that the addition of aluminum sol to the SiO2 aerogel inhibited phase transitions, and both acidic silica sol and aluminum sol particles enhanced the aerogel structure, contributing to a marked improvement in high-temperature resistance. [ABSTRACT FROM AUTHOR]

Published
2024
Full Text
View/download PDF

Catalog

Books, media, physical & digital resources
See catalog results