Session: 10.4.1 - Vortex Dynamics I

Paper Number: 158102

158102 - Study of Wake Dynamics and Turbulent Heat Transport in Single Jet and Multiple Jets With Different Jet Spacing Using Dynamic Mode Decomposition 

Abstract: 

Air-cooled heat exchangers (ACHEs) are equipped with large fans and placed on top of high pipe racks in liquefied natural gas (LNG) plants, and they discharge a large amount of hot air into the atmosphere. The performance of ACHEs can be significantly reduced if the hot exhaust air recirculates back into the ACHEs under crosswind conditions, leading to hot air recirculation (HAR). The flow patterns of hot air discharged from a single Air-Cooled Heat Exchanger (ACHE) fan and multiple ACHE fans under crosswind conditions are similar to those of a jet in crossflow (JICF) and multiple jets in crossflow (MJICF), respectively. Understanding the physics of JICF and MJICF is essential for predicting Hot Air Recirculation (HAR) phenomena, thereby contributing to increased production efficiency in LNG plants.

This study aims to elucidate the underlying physics of JICF and MJICF, with a particular emphasis on the differences in vortical structures and jet interactions between adjacent jets with different jet spacings. Large eddy simulations (LES) were conducted for a single jet and five spanwise jets with different jet-to-jet spacings. The jet-to-crossflow velocity ratio was 3.3, and the Reynolds number, based on the crossflow velocity, was 2100. A verification study of a single jet demonstrated that the LES accurately reproduces the characteristic vortex structures of a single jet in crossflow and provides good predictions by comparing the predictions of the mean velocity magnitude, RMS fluctuations of the velocity magnitude, mean temperature, and RMS fluctuations of the temperature along the vertical lines at different X locations on the central plane with experimental data.

Proper orthogonal decomposition (POD) analysis was performed on two-dimensional snapshots of flow fields for a single jet and multiple jets with a spacing of 1.6D (where D is the jet nozzle diameter), and the results were presented at FEDSM 2024. As a further study, POD and dynamic mode decomposition (DMD) analysis were applied to the three-dimensional flow fields of a single jet and multiple jets with different jet spacings to identify differences in the dominant shedding modes of vortical structures and their associated shedding frequencies. The DMD analysis reveals that the complete vortical structures corresponding to different shedding modes, providing deeper insights into the vortex dynamics in JICF and MJICF. It is also found that the interactions between adjacent jets vary significantly depending on the jet-to-jet spacing. Furthermore, the turbulent heat transport for different jet spacings was compared to evaluate the impact of jet spacing on thermal behavior. The dominant components of turbulent heat transport, u’T’, v’T’ and w’T’ exhibit notable changes for different jet spacings.

Presenting Author: Xidong Hu Institute of Science Tokyo

Presenting Author Biography: I am a PhD student in Institute of Science Tokyo and also a principal CFD engineer in a global engineering company in the energy industry.