# Reduction of the Cavitation Noise in an Automotive Heater Core
## 1 Introduction
[23] studied wall injection effects on diesel injector flows. [PERSON] et al. [24] performed spectral analysis of pressure, noise, and vibration in convergent-divergent nozzles. Cavitation phenomena in automotive systems have been widely studied due to their detrimental impact on system performance and component durability. For instance, vibration-based diagnostic methods have been employed to detect cavitation in gerotor pumps used for engine lubrication, offering a non-intrusive and effective means of monitoring [25; 26]. Additionally, recent numerical modeling efforts have addressed cavitation-induced damage in critical components such as the connecting rod big end bearing, further emphasizing the need for both experimental and computational approaches to understanding cavitation in complex engine systems [27]. These studies collectively underscore the importance of cavitation monitoring, aligning with the objectives of our work on heater core-induced noise and vibration. On the other hand, [PERSON] et al. [28] investigated cavitation noise in diesel engine main bearings, attributing it to oil film cavitation, journal instability, and excitation forces. Given this research gap, the present study focuses on cavitation noise originating from the heater core of a compact passenger vehicle. The goal is to deepen the understanding of this phenomenon and offer practical mitigation strategies. Despite the breadth of existing literature on cavitation in automotive systems--particularly in components such as oil pumps, bearings, injectors, and valves--there remains a lack of focused investigation into cavitation phenomena occurring within the heater core, especially under transient cold-start conditions. Previous research has primarily addressed cavitation in rotating or high-pressure components, often emphasizing fluid delivery performance, component degradation, or lubrication system reliability. However, little attention has been given to cavitation-induced noise and vibration in low-pressure, thermally regulated circuits such as those found in HVAC systems. This study addresses this critical research gap by examining a real-world case of abnormal noise reported in a compact passenger vehicle, identifying its root cause as cavitation in the heater core, and validating the findings through a combination of experimental noise and vibration measurements, flow simulations, and flow visualization techniques. The proposed noise mitigation strategies derived from this integrated approach offer new insights applicable to the design and refinement of thermal management systems in future vehicles. At the outset, the cause of the abnormal noise during high-speed engine operation in a small-displacement, four-cylinder turbocharged engine during cold starts was unknown. This paper documents the research process undertaken to identify the source and propose solutions. Section 2 describes experiments that measured noise and vibration during noise events and led to the identification of cavitation noise. Section 3 presents flow analysis simulations used to estimate the cause and location of cavitation, followed by flow visualization experiments using a transparent pipe to validate the findings and measure noise and vibration. Section 4 discusses noise reduction strategies, first evaluated through simulations and then experimentally verified. Finally, Section 5 summarizes the findings and conclusions of this study.