Effect of Flow Approach Angle on Flow Periodicity and Acoustic Resonance in Triangular Tube Bundles

Abstract

Abstract. This study experimentally investigates the excitation of acoustic resonance in a small pitch ratio triangular tube array (P/D = 1.5), with a focus on the influence of the flow approach angle on the intensity of acoustic resonance excitation and the associated periodic flow instabilities that trigger self-sustained acoustic resonance. The objective is to identify the dominant mechanisms sustaining acoustic resonance in heat exchanger applications, particularly when the flow direction deviates from being strictly normal to the tube array. Three flow approach angles—0 deg, 15 deg, and 30 deg—were analyzed, covering the standard triangular configurations (parallel triangular tube array at 0 deg and normal triangular tube array at 30 deg) as well as an intermediate case (15 deg). Periodic flow structures and their corresponding Strouhal numbers were evaluated for each configuration, enabling the identification of the flow instabilities responsible for initiating and sustaining acoustic resonance. The results show that the maximum acoustic pressure at resonance is highly sensitive to the flow approach angle. At a 0 deg flow approach angle, the highest sound pressure levels (SPLs) were recorded, exceeding 162 dB. This strong flow-induced acoustic resonance led to high-cycle fatigue failure of multiple tubes, despite the tubes being rigidly supported within the bundle. This highlights the critical importance of considering flow-induced acoustic resonance during the design of tube arrays for industrial applications such as heat exchangers. Neglecting this phenomenon can lead to catastrophic consequences.