Effects of ambient pressure on cavitation in the nozzle and the discharged liquid jet

Cavitation in the nozzle plays an important role in the atomization of the discharged liquid jet. Because of this, understanding in-nozzle cavitation is very important for the control of spray characteristics. However, in-nozzle cavitation is not fully understood at present, in part because it is affected by various factors, such as fluid properties, injector geometries, and ambient pressure. Although it is obvious that ambient pressure hinders cavitation development in the nozzle, the extent of the effect has not been quantitatively predicted yet. In the present study, visualization of cavitation in an enlarged two-dimensional (2D) transparent nozzle and the discharged liquid jet is carried out under various ambient pressure P-a (P-a = 0.1, 0.2, 0.3, 0.4, and 0.5 MPa). From the flow visualization result, an image analysis is carried out to obtain the experimental data on the effects of ambient pressure on cavitation length L-c, cavitation width W-c, and liquid jet angle 0. Finally, a set of correlations on L-c, modified cavitation number sigma(c), jet angle theta, and the Weber number We at various ambient pressures are proposed, based on the image analysis results.