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

This study experimentally investigates acoustic resonance in a small pitch ratio triangular tube array (P/D = 1.5), emphasizing the impact of flow approach angle on the intensity of acoustic resonance and the associated periodic flow instabilities. The objective is to determine the dominant mechanism 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°, 15°, and 30°—were analyzed, covering the standard triangular configurations (parallel triangular tube array at 0° and normal triangular tube array at 30°) as well as an intermediate case (15°). The results indicate that the maximum acoustic pressure at resonance is highly sensitive to the flow approach angle. Furthermore, periodic flow structures and their corresponding Strouhal numbers were evaluated for each angle, identifying the flow periodicity responsible for triggering acoustic resonance.