Session: FSI-02-01 Flow-induced Vibration I

Paper Number: 63015

Start Time: Tuesday, July 13, 2021, 05:00 PM

63015 - Equivalent Diameter for Predicting Vortex Shedding of Finned Cylinders in Cross-Flow 

In the past 100 years, progress has been made in improving the heat transfer performance of tubular, gaseous heat exchangers. This has been accomplished by the addition of fins around the outer tube circumference.  The addition of fins enhances convective heat transfer by increasing the exposed surface area to the gaseous flow. Presently, there are many different types of finned tubes utilized in the heat exchanger industry. The finned tube type used and their heat transfer performance is dependent on the industrial application. Though the fins greatly enhance heat transfer performance compared to a bare tube, recent investigations have shown that the fins affect the near-wake flow characteristics making them more or less susceptible to a phenomenon known as flow-excited acoustic resonance.  Flow-excited acoustic resonance may materialize if the frequency of the periodic flow structure (vortex shedding) in the wake of the finned tubes coincides with an acoustic resonant mode of the heat exchanger enclosure. The onset of flow-excited acoustic resonance is problematic as it results in the generation of intense tonal noise which can negatively affect the service life of the heat exchanger, damage critical equipment, and significantly elevate environmental noise affecting the safety and health of nearby workers. It is thus imperative that the onset of flow-excited acoustic resonance is predicted at the early heat exchanger design phase so it does not emerge during operation. This can be done by predicting the vortex shedding frequency emanating from the finned tubes and ensuring that it does not coincide with one of the heat exchanger acoustic resonant modes.

The Strouhal relation is used to predict the vortex shedding frequency which is a function of the flow velocity and characteristic length scale. In the case of a bare circular tube, the characteristic length scale is the outer diameter. In the case of a finned cylinder, the characteristic length scale is its equivalent diameter which is a function of the fin pitch, fin thickness, root, and fin diameter. Various equivalent diameters have been proposed in the literature to predict the vortex shedding frequency emanating from various types of finned tubes. However, none of the equivalent diameter formulas presented in the literature are sufficient in capturing the vortex shedding frequency of crimped spirally finned cylinders, except for the recently developed modified equivalent diameter formula. The use of crimped spirally finned cylinders are increasing in popularity due to their enhanced heat transfer performance compared to a non-crimped (solid) spirally finned cylinder.

 In the present paper, the vortex shedding frequency of various finned tubes, such as straight circular fins, spiral fins, spiral crimped fins, and serrated fins are experimentally investigated. The experiments are performed in a high-speed open-circuit wind tunnel located at the Aeroacoustics and Noise Control Laboratory situated at Ontario Tech University, Oshawa, Canada. The applicability and usage of various equivalent diameter formulas presented in the literature for the different finned cylinder types are studied. A summary of the results is presented in this paper.

Presenting Author: Mohammed Alziadeh Ontario Tech University

Authors:

Mohammed Alziadeh Ontario Tech University
Atef Mohany Ontario Tech University