Standoff Distance in Ultrasonic Pulsating Water Jet

Abstract

The water hammer effect is the basis of technologies which is artificially responsible for the decay of continuous jets. A recently developed technique enhances the pressure fluctuations using an acoustic chamber, leading to enhanced erosion effects for various water volume flow rates. The optimum standoff distance for an ultrasonic enhanced water jet is not appropriately estimated using an inclined trajectory. The objective of this study is to comprehend the true nature of the interaction of the standoff distance following the stair trajectory and traverse speed of the nozzle on the erosion depth. Additionally, it also critically compares the new method (staircase trajectory) that obeys the variation in frequency of the impingements for defined volume flow rates with the inclined trajectory. In this study, at constant pressure (p = 70 MPa), the role of impingement distribution with the variation of traverse speed (v = 5–35 mm/s) along the centerline of the footprint was investigated. The maximum erosion depth corresponding to each traverse speed is observed at approximately same standoff distance (65 ± 5 mm) and decreases with the increment in traverse speed (h = 1042 and 47 µm at v = 5 and 35 mm/s, respectively). The results are attributed to the variation in the number of impingements per unit length. The surface and morphology analysis of the cross-section using SEM manifested the presence of erosion characteristics (micro-cracks, cavities, voids, and upheaved surface). By varying the water cluster, different impingement densities can be achieved that are suitable for technological operations such as surface peening, material disintegration, or surface roughening.

Surface and Subsurface Analysis of Stainless Steel and Titanium Alloys Exposed to Ultrasonic Pulsating Water Jet

“…The second method to increase the efficiency of the water jet is the forced decaying of the continuous water jet into discrete clusters to use the hammer effect [6]. By periodically applying impact pressure in the form of a water droplet, which has higher pressure values than stagnation pressure [7], in a continuous stream, it is possible to erode the material at lower operating pressures of 10-100 MPa [8]. The advantages of pulsating water jets (PWJs) can be grouped into three main areas: first, they are more efficient compared with continuous water jets under the same hydraulic conditions [9]; second, the pressure acts upon the impacted area in a periodic manner, which can be used Materials 2021, 14, 5212 2 of 20 for surface reinforcement, such as the peening method [10,11]; and third, A PWJ acting without added solid (abrasive) particles can be used in the treatment of structural parts for medical applications [12][13][14][15].…”

“…An effective method to overcome this issue is to add mechanical vibrating droplets (needle) inside a pressure chamber close to the nozzle outlet. A problem with this method is the short life of the needle [ 8 ]. A self-resonating nozzle works using a specially made cavity inside the nozzle.…”

“…In the termination stage, i.e., the final stage, monodisperse droplets with lesser mass than the clusters in the acceleration and depletion stage interact with the surface. A further study proved the erosion shift of the grooves in terms of the pressure variability and distribution density of water clusters [ 8 ].…”

Utilizing the water hammer effect to enhance the mechanical properties of AISI 304 welded joints

“…The advantage of this technology is the low operating technological parameters as compared to conventional methods of water jet technology. In general, studies have focused on the advanced stages of erosion [16,17]. However, current research is focused on a thorough analysis of the so-called incubation phase.…”

Ultrasonic Pulsating Water Jet Peening: Influence of Pressure and Pattern Strategy

“…The high-pressure water fluctuations pass through the nozzle exit, where they are converted into a high-velocity modulated stream; then, at a certain distance from the exit, discrete bunches of water elements begin to form, which subsequently impact the material [20]. The distance required for the generation of discrete clusters of water elements is very important for the full utilization of the hammer effect [21]. When a high-pressure water jet (100 MPa or more) is used, this distance required for the formation of water agglomerates is rapidly increased and, thus, there is not much of an effect on the material [22].…”