**4. Effects of pulsating water jets on materials**

Effects of pulsating water jets with the frequency of 20 kHz were tested on various types of materials, such as metals, rocks and concrete. Tested materials were exposed to the action of

Model Solo 120 with pulse duration 3-5 ns; the optical system was used to produce 1 mm thick sheet of light. An example of the pulsating jet visualized by high-speed camera can be

Fig. 10. The instantaneous structure of the pulsating water jet generated at 30 MPa (high-

Fig. 11. The instantaneous structure of the pulsating water jet generated at 30 MPa (PIV

Fig. 12. The instantaneous structure of the fan pulsating water jet generated at 20 MPa

Effects of pulsating water jets with the frequency of 20 kHz were tested on various types of materials, such as metals, rocks and concrete. Tested materials were exposed to the action of

pulsating water jet generated at a pressure of 20 MPa.

(illumination by pulsed laser, camera Nikon D70s)

**4. Effects of pulsating water jets on materials** 

The fan (flat) pulsating water jet visualization was performed using the pulsed laser New Wave Research and digital camera Nikon D70s. Figure 12 shows the morphology of fan

seen in Fig. 10, the same jet visualized by PIV system is presented in Fig. 11.

speed camera)

system)

diverse types of jets: single round and fan pulsating jets as well as rotating pulsating jets. The effects of pulsating jets were evaluated in terms of cutting depth, rate of mass-loss or volume removal rate respectively and compared with the effects of continuous water jets under the same operating conditions.

Obtained results show clearly the supremacy of pulsating water jets over continuous ones in terms of their effects on material. Figures 13 to 15 illustrate the effects of various types of both pulsating and continuous jets on metal, rock and concrete samples. Differences in the surface structures created by pulsating and continuous water jets on individual materials are clearly visible in the above mentioned figures. An example of erosion effects of pulsating fan water jets (generated at various pressures) on aluminium samples at variable stand-off distance is presented in Figure 16.

Fig. 13. Comparison of effects of pulsating (P) and continuous (C) water jets on samples of: a) mild steel (pressure 40 MPa, nozzle dia. 1.98 mm, traverse speed 0.03 m.min-1, standoff distance 140 mm), b) brass (pressure 40 MPa, nozzle dia. 1.98 mm, traverse speed 0.03 m.min-1, standoff distance 140 mm), c) duralumin (pressure 50 MPa, nozzle diameter 1.45 mm, traversing speed 0.05 m.min-1, standoff distance 60 mm) and d) basalt (pressure 50 MPa, nozzle diameter 1.45 mm, traversing speed 1.0 m.min-1, standoff distance 40 mm (P) and 20 mm (C))

Use of Acoustic Waves for Pulsating Water Jet Generation 339

Results of the measurement of surface roughness characteristics on surfaces created by fan pulsating jets indicate that the characteristics are strongly influenced by both the standoff distance and the operating pressure. An example of the influence of a standoff distance on arithmetic mean roughness (SRa) and average maximum height roughness (SRz) can be seen in Figures 17 and 18, respectively. It should be pointed out that surface roughness (both SRa and SRz) produced by the pulsating fan water jet out of the range of "optimum" standoff distances (where the pulsating jet acts as a continuous jet) correspond to those produced by continuous jets reported by Kunaporn et al. (2009). On the other hand, the fan pulsating water jet produces surfaces with much higher values of the surface roughness (up to 20 times higher) within the "optimum" range of standoff distances (where the pulses are well-

**20 MPa 30 MPa 50 MPa 70 MPa**

Fig. 16. Top: Pulsating fan water jets generated by nozzle with equivalent of diameter 1.10 mm and spraying angle of 10° at various operating pressures. Scale on the left side of photographs represents standoff distance in millimeters. Dots indicate the range of standoff distances where maximum erosion effects of pulsating fan water jet occur. Bottom: Erosion effects of the above

mm mm mm mm



20

30

40

50

60

70

80

10

20

20


30

40

50

60

70

80

30

40

50

60

70

80

pulsating fan water jets on duralumin samples. Scale on the right side of photographs indicates standoff distance in millimeters; scale on the bottom indicates width in millimeters

developed in the jet) compared to continuous jets.

20


30

40

50

60

70

80

Fig. 14. Comparison of effects of rotating pulsating (A) and rotating continuous (B) water jets on concrete sample (Vr – removed volume, pressure 30 MPa, nozzle diameter 2x1.47 mm, traversing speed 0.5 m.min-1, standoff distance 40 mm (A) and 20 mm (B))

Fig. 15. Comparison of effects of fan pulsating (A) and fan continuous (B) water jets on concrete samples (Vr – removed volume, pressure 30 MPa, equivalent nozzle diameter 2.05 mm, traversing speed 0.2 m.min-1, standoff distance 40 mm)

**A B**

Fig. 14. Comparison of effects of rotating pulsating (A) and rotating continuous (B) water jets on concrete sample (Vr – removed volume, pressure 30 MPa, nozzle diameter 2x1.47

V = 4 r cm<sup>3</sup>

Fig. 15. Comparison of effects of fan pulsating (A) and fan continuous (B) water jets on concrete samples (Vr – removed volume, pressure 30 MPa, equivalent nozzle diameter 2.05

mm, traversing speed 0.2 m.min-1, standoff distance 40 mm)

mm, traversing speed 0.5 m.min-1, standoff distance 40 mm (A) and 20 mm (B))

3

V = 22 cm <sup>r</sup>

Results of the measurement of surface roughness characteristics on surfaces created by fan pulsating jets indicate that the characteristics are strongly influenced by both the standoff distance and the operating pressure. An example of the influence of a standoff distance on arithmetic mean roughness (SRa) and average maximum height roughness (SRz) can be seen in Figures 17 and 18, respectively. It should be pointed out that surface roughness (both SRa and SRz) produced by the pulsating fan water jet out of the range of "optimum" standoff distances (where the pulsating jet acts as a continuous jet) correspond to those produced by continuous jets reported by Kunaporn et al. (2009). On the other hand, the fan pulsating water jet produces surfaces with much higher values of the surface roughness (up to 20 times higher) within the "optimum" range of standoff distances (where the pulses are welldeveloped in the jet) compared to continuous jets.

Fig. 16. Top: Pulsating fan water jets generated by nozzle with equivalent of diameter 1.10 mm and spraying angle of 10° at various operating pressures. Scale on the left side of photographs represents standoff distance in millimeters. Dots indicate the range of standoff distances where maximum erosion effects of pulsating fan water jet occur. Bottom: Erosion effects of the above pulsating fan water jets on duralumin samples. Scale on the right side of photographs indicates standoff distance in millimeters; scale on the bottom indicates width in millimeters

Use of Acoustic Waves for Pulsating Water Jet Generation 341

Presented results of the analytical solution and numerical simulation of the transmission of acoustic waves in high-pressure system represent the first step in gaining knowledge regarding processes of generation and propagation of high-frequency pressure pulsations in the liquid under high pressures and their influence on forming and morphology of

Results obtained from the visualization of pulsating water jets are used in studying of the characteristics of the jets and to verify results obtained from numerical simulation of the process of generating and forming of pulsating water jets. Laboratory and pilot tests of effects of pulsating water jets on various materials showed clearly the potential of pulsating

It can be concluded that the research presented in the paper contributed to better knowledge of processes occurring in areas of generation and propagation of high-frequency pressure pulsations in the liquid under high pressure, their influence on forming and morphology of pulsating water jets and effects of the jets on materials. However, it is still necessary to further study problems of the efficient transfer of the high-frequency pulsation energy to longer distances in the high-pressure system. This will enable creation of the highly effective

The chapter has been done in connection with project Institute of clean technologies for mining and utilization of raw materials for energy use, reg. no. CZ.1.05/2.1.00/03.0082 supported by Research and Development for Innovations Operational Programme financed by Structural Founds of Europe Union and from the means of state budget of the Czech Republic. Presented work was also supported by the Academy of Sciences of the Czech

Bowden, F. P., & Field, J. E. (1964). The brittle fracture of solids by liquid impact, by solid

de Haller, P. (1933). Untersuchungen über die durch Kavitation hervorgerufenen Korrosionen. *Schweizerische Bauzeitung*, Vol. 101, No. 21& 22, pp. 243-246,260-264 Hancox, N. L., & Brunton, J. H. (1966). The erosion of solids by the repeated impact of liquid

Kunaporn, S., Chillman A., Ramulu, M., & Hashish, M. (2009). Effect of waterjet formation

Pianthong, K., Zakrzewski, S., Behnia, M., & Milton, B. E. (2003). Characteristics of impact

*Mathematical and Physical Sciences*, Vol. 282, No. 1390, pp. 331-352

impact, and by shock. *Proceedings of the Royal Society of London. Series A,* 

drops. *Philosophical Transactions of the Royal Society of London. Series A, Mathematical* 

on surface preparation and profiling of aluminum alloy. Wear, Vol. 265, No. 1-2,

driven supersonic liquid jets. *Experimental thermal and fluid science*, Vol. 27, No. 5,

jets to improve the performance of water jetting technology significantly.

Republic, project No. AV0Z30860518. Author is thankful for the support.

*and Physical Sciences*, Vol. 260, No. 1110, pp. 121-139

pulsating liquid jet with required properties.

**6. Acknowledgements** 

**7. References** 

pp. 176-185

pp. 589-598

**5. Conclusions** 

pulsating liquid jets.

Results of the research of effects of pulsating jets on various materials obtained so far indicate that the pulsating jets can be used advantageously for the removal of surface layers of materials and/or "rough" cutting. However, further research will be necessary to be able to use the pulsating water jets in applications of precise cutting.

Fig. 17. Influence of a standoff distance on arithmetic mean roughness (SRa) of the surface created by the action of pulsating fan water jet generated by the fan jet nozzle with equivalent of diameter 1.10 mm and spraying angle of 10°

Fig. 18. Influence of a standoff distance on average maximum height roughness (SRz) of the surface created by the action of pulsating fan water jet generated by the fan jet nozzle with equivalent of diameter 1.10 mm and spraying angle of 10°
