Cavitation onset caused by acceleration

Abstract

Striking the top of a liquid-filled bottle can shatter the bottom. An intuitive interpretation of this event might label an impulsive force as the culprit in this fracturing phenomenon. However, highspeed photography reveals the formation and collapse of tiny bubbles near the bottom before fracture. This observation indicates that the damaging phenomenon of cavitation is at fault. Cavitation is well known for causing damage in various applications including pipes and ship propellers, making accurate prediction of cavitation onset vital in several industries. However, the conventional cavitation number as a function of velocity incorrectly predicts the cavitation onset caused by acceleration. This unexplained discrepancy leads to the derivation of an alternative dimensionless term from the equation of motion, predicting cavitation as a function of acceleration and fluid depth rather than velocity. Two independent research groups in different countries have tested this theory; separate series of experiments confirm that an alternative cavitation number, presented in this paper, defines the universal criteria for the onset of acceleration-induced cavitation. . More commonly, sudden valve closing inside of a water pipe can cause a loud hammering sound due to the collapse of cavitation, resulting in damage on the inner walls (4). The effects of blast and impact that cause traumatic brain injury from cavitation have also been investigated (5, 6). To avoid cavitation-induced damage (7-9), it is crucial to predict the onset of cavitation.Cavitation onset in a high-speed flow [e.g., flow around propellers and in pumps (10)] can be characterized using a variant of the Euler number known as the cavitation number (11,12). The cavitation number is typically of the formwhere pr is the reference pressure, pv is the liquid vapor pressure, ρ is the liquid density, and v is the local velocity (13-16). This cavitation number is a ratio of the pressure difference to the pressure drop due to the fluid momentum. The large momentum of the fluid dominates when C 1, inducing cavitation. However, when C 1, the pressure at all locations is above the threshold for bubble formation, making cavitation unlikely. Practically, several advanced coefficients have been proposed to estimate cavitation inception for various geometries (16).However, the conventional cavitation number (C ) could incorrectly predict the cavitation onset in a liquid accelerated in a short amount of time. For example, the cavitation event that breaks the bottle in Fig. 1A has a maximum velocity of v ≈ 2 m/s, which yields the cavitation number C ∼ O(10 2 ). For the falling tube case in Fig. 1B a similar calculation leads to C ∼ O(10 2 ) (Table S1), whereas the conventional cavitation number requires C 1 (16). Thus, a new cavitation number is required to define the physics of cavitation onset.In the past, researchers have conducted similar experiments with a bullet-piston device to predict the tensile strength of a liquid, including pure water (17). They reported that the ...

Gelatine cavity dynamics of high-speed sphere impact

“…2017, 2018; Pan et al. 2017) and fabrication of drug delivery systems (Tagawa et al. 2013; Battula, Menezes & Hosseini 2016; Moradiafrapoli & Marston 2017; Kiyama et al.…”

Knifefish’s suction makes water boil

“…It has recently been demonstrated that cavitation induced by an impulsive system can be better defined by acceleration rather than speed 1 . Here we calculated the cavitation number as Ca = (p r − p v )/(ρLa max ) 1 , where p r is the atmospheric pressure, p v is the vapor pressure, ρ is the water density, and L is the distance between the start and end positions of water level in the tube, respectively. We found that knifefish suction feeding generates Ca of 0.65 (± 0.20 SD, N = 4), which sufficiently meets the criteria to generate cavitation (Ca < 1).…”

“…Cavitation bubbles in a liquid are induced by intense and sudden changes of local pressure 1 . These collapsing bubbles can produce intense compressional waves and extremely high temperatures, as well as serious damage on structures.…”

Acceleration-induced pressure gradients and cavitation in soft biomaterials

“…Currently, p ∝ ah (see Eq. S3 in the supplementary document) is often used to estimate p where a and h are acceleration and a coordinate of the sample in the impact direction because directly measuring p in pure water 24 and soft gels 15 during impact is still experimentally challenging. In this regard, we theoretically consider below how p , λ and h are linked to each other and show p ∝ ah is not a good estimation for the acceleration-induced pressure gradient for soft gels.…”

“…One notable advance is in the characterization of cavitation properties for soft materials under an impulsive force 15 , 24 where the critical acceleration that corresponds to the onset of the bubble formation and bursts is quantitatively measured. While the acceleration-induced pressure is the primary driving force for this rapid material deformation associated with bubble dynamics in pure water and gelatin samples, the spatio-temporal dynamics in soft material samples during mechanical impact remains largely unknown.…”