## 1 Introduction
[25] to study the impinging flow field of the SC-CO\({}_{2}\) jet in the bottom hole. Their simulation results showed that the Joule-Thompson throttling effects are much more prominent at higher inlet fluid temperature and larger pressure drops. Additionally, the abrasive SC-CO\({}_{2}\) jet, formed by adding solid particles into the SC-CO\({}_{2}\) jet, was numerically simulated by [PERSON] et al. [16], and they found that the two-phase axial velocities of the abrasive SC-CO\({}_{2}\) jet is much higher than those of the abrasive water jet. Moreover, by methods of laboratory experiment and numerical simulation, [PERSON] et al. [18] studied the bottom hole pressure and temperature distributions during the SC-CO\({}_{2}\) jet drilling in detail. They confirmed that with the increase of standoff distance, the bottom hole temperature decreases while the bottom hole pressure increases first and then decreases. Besides, comprehensive methods of numerical simulations and lab experiments were carried out by [PERSON] et al. [11] to investigate the influences of the ambient pressure and the standoff distance on the impinging pressure and perforation performance of the SC-CO\({}_{2}\) jet. They confirmed that when the pressure difference is kept constant, the effective impinging pressure hardly changes with ambient pressure, but the eroded depth increases at first and then decreases, bounded by the critical pressure of SC-CO\({}_{2}\). As the standoff distance extends, the eroded diameter increases at first and then decreases. Although a considerable amount of research has been carried out on the SC-CO\({}_{2}\) jet, to the best of our knowledge, there is so far little literature on how nozzle configuration influences the rock erosion performance of the jet. However, when the nozzle configuration is changed, the flow of SC-CO\({}_{2}\) fluid inside the nozzle will change, which could result in different flow characteristics of the jet ejected from the nozzle exit. Since flow characteristics of the SC-CO\({}_{2}\) jet can have a great influence on the impingement of the jet on rocks, nozzle configuration is expected to put a significant impact on the rock erosion behaviors of the SC-CO\({}_{2}\) jet. Furthermore, according to the basic theory of jet dynamics [26; 27; 28; 29; 30], it is well known that a Laval nozzle can easily accelerate the jet fluid medium with significant compressibility to a supersonic speed under certain conditions, which is difficult for a commonly used convergent nozzle. Also, [PERSON] et al. [31] experimentally concluded that different types of nozzles can provide various flow velocities of the jet, and a supersonic jet without chocking can be achieved using a Laval nozzle which is beneficial for improving coating density and adhesion in wire spray. In addition, the compressibility of the fluid plays a key role in the process of fluid accelerated by a Laval nozzle [27; 28; 29]. Meanwhile, it is reported that SC-CO\({}_{2}\) has significant compressibility [32; 33; 34]. Therefore, it is reasonable to speculate that the Laval nozzle can alter the flow field of the SC-CO\({}_{2}\) jet and should have great effects on the rock erosion characteristics of the jet. Moreover, a Laval nozzle was employed by [PERSON] et al. [35] to accelerate a jet to supersonic levels, then the high speed jet was used to erode cylindrical brittle gypsum deposits. The results showed that the gypsum deposits can be effectively broken by the high-speed jet issuing from the Laval nozzle and the failure behaviors of the asymmetric deposits depend on orientation. This is conducive to further optimizing the performance of sootblower which is used to clean fireside deposits formed on tubes in boilers. The present paper gives an experimental investigation on the effects of nozzle configuration including a convergent nozzle, and two Laval nozzles on the rock erosion characteristics of the SC-CO\({}_{2}\) jet under various pressures and temperatures, with the purpose of enhancing the rock erosion capability of the jet.