Self-excited Oscillation Pulsed Jet Research Articles

Impact frequency variation of self-excited oscillation pulsed supercritical carbon dioxide jets

In order to obtain the impact frequency of resonant coal breaking by self-excited oscillation pulsed supercritical carbon dioxide (SC-CO2) jet, large eddy simulation was used to analyze the formation and development process of self-excited oscillation pulsed SC-CO2 jet, the variation of jet impact frequency in the nozzle and the free flow field, and the variation of jet impact frequency at different positions in the jet axis and under different cavity lengths. The test device of jet impact frequency was developed, and experiments were performed to verify the conclusions of the numerical simulations. The results show that the frequency of the self-excited oscillation pulsed SC-CO2 jet is different in the nozzle and the free flow field. In the nozzle, the frequency generated by the fluid disturbance is the same, and the jet frequency at the exit of the nozzle is consistent with that inside the nozzle. In the free flow field, due to the compressibility of CO2, the pressure, velocity and other parameters of SC-CO2 jets have obvious fluctuation patterns. This feature causes the impact frequency of the self-excited oscillation pulsed SC-CO2 jet to decrease gradually in the axis. Changing the cavity length allows the adjustment of the jet impact frequency in the free flow field by affecting the disturbance frequency of the self-excited oscillation pulsed SC-CO2 jet inside the nozzle.

Study on the impacting performance of a self-excited oscillation pulsed jet nozzle

The pulsive jet nozzle, which converts the continuous jet into a pulsive jet, is widely used in downhole well operations, such as drilling and perforation. In this paper, a self-excited oscillation pulsed jet nozzle is proposed basing on the Coanda effect. The effects of nozzle design, inlet flow rate, and target distance on the jet dynamics, such as the pulsive characteristics and impacting performance, were investigated. The transient flow pattern was studied with a high-speed camera, which showed a good agreement with the numerical results. Furthermore, with the increase of the inlet flow, the pulsation amplitude of impacting pressure of the Coanda nozzle increased. Based on the obtained data, the relationship between the pulsive frequency and Reynolds number and that between Strouhal number and Reynolds number was revealed. Under a confining pressure of 30 MPa, a target distance of 70 mm, and an inlet flow rate of 15 m/s, the error between the numerical impacting pressure and the experimental value was 9.7%, which confirmed the numerical approach could be used to predict the transient jet process. The obtained results can guide the design of a self-excited oscillation pulse jet nozzle and its oilfield application. • A self-excited oscillation pulsed jet nozzle with Coanda effect is proposed. • Computational fluid dynamics was applied to simulate the pulsive behavior. • Process parameters shown significant influence on the pulsive characteristics. • An error of 9.3% was achieved between numerical and experimental results.

Investigation of the Jet Characteristics and Pulse Mechanism of Self-Excited Oscillating Pulsed Jet Nozzle

Self-excited oscillation pulse jet technology is widely used to clean sediment from oil storage tanks. Its successful application is dependent on jet performance. As the cleaning requirements of the oil industry increase, it is necessary to optimise the structure of self-excited oscillation pulsed jet nozzles (SOPJNs) to optimise cleaning and energy efficiencies. In this study, the jet performance of a SOPJN is modelled and analysed based on computational fluid dynamics with consideration of a large eddy simulation and homogeneous cavitation. The modelling results are highly consistent with experimental results. The effects of the SOPJN’s inlet diameter, cavity diameter, cavity length, wall reflection angle, and inlet pressure on the jet’s peak velocity, oscillation frequency, and cavitation number were analysed. The results show that the oscillation frequency decreases with the increase of the inlet diameter d1, cavity diameter D, cavity length L and reflection angle of wall α. Optimisation of the SOPJN inlet diameter, cavity length, and wall reflection angle produced a jet with a high peak velocity and strong cavitation. The optimal nozzle cavity diameter strengthens cavitation, while the peak velocity fluctuates as the cavity diameter increases. The peak velocity increases with the inlet pressure, while the increasing rate of the peak velocity decreases. The results of this study can be used in the design and optimisation of similar nozzle structures for improved pulse jet cleaning.

Investigation of the impact characteristics and pulse mechanism of a self-excited aspiration pulsed jet device

In this paper, based on the traditional low-frequency self-excited oscillation pulsed jet device, a self-excited aspiration pulsed jet device is designed. For the structural parameters, including the aspiration capacity, impact characteristics, and pulse generation mechanism, the jet impingement is analyzed experimentally under the aspiration and non-aspiration conditions. It was found that, compared to the non-aspiration condition, the maximum aspiration capacity, the increase of instantaneous impact force, and the obvious pulse period, which is between 1 and 2 s, can be obtained under appropriate structural device parameters. The db10 orthogonal wavelet and the empirical mode decomposition methods can decompose instantaneous impact force into time-varying and fluctuating impact forces. However, under different confining pressures, each method has its own advantages in extracting the time-varying impact force. In addition, after aspiration, the confining pressure and target distance have little effect on the pulse frequency of the time-varying impact force, while higher confining pressure and larger target distance result in smaller pulse amplitude. Under different confining pressures and target distances, after aspiration, the time-average impact force at and near the target center increases, while far away from the target center it decreases. Moreover, after aspiration, the fluctuation amplitude and intensity of the fluctuating impact force increase, and the confining pressure has little effect on the pulse frequency. However, higher confining pressure results in smaller fluctuation amplitude, intensity, and energy spectral density. After aspiration, subsonic and supersonic water flows are formed inside the device. In addition, it was found that there is a relationship between the aspiration capacity, the time-variation pressure of the collision body measuring point, and the impact force. Based on this relation, the pulse generation mechanism of the device is revealed.

Study on velocity and pressure characteristics of self-excited oscillating nozzle

The mechanism of the self-excited oscillation pulsed jet is still in a period of continuous improvement, and the application breadth and depth of the self-excited oscillation nozzle are significantly limited since the turbulent flow field inside the self-excited oscillation nozzle is exceptionally complex. In this study, computational fluid dynamics numerical simulation and experimental research methods are combined. By changing the structural parameters of self-excited oscillating nozzles, the velocity and pressure characteristics of the self-excited oscillating nozzles were compared and analyzed to determine the important factors that influenced the effect of pulsed jet. These findings demonstrated that the periodic expansion and contraction of the low-pressure vortex ring in the self-excited oscillation nozzle chamber will cause the pressure of the nozzle outlet section to change periodically. The periodic high-voltage blocking and low-pressure speedup of the outlet directly correlate with the pulsed jet. This study shows the reasonable size design range of the self-excited oscillation nozzle, which can guide the design and practical application of the nozzle, as well as provide the theoretical basis for perfecting the self-excited oscillation pulsed jet theory.

Large Eddy Simulation of Self-Excited Oscillation Pulsed Jet (SEOPJ) Induced by a Helmholtz Oscillator in Underground Mining

Pulsed waterjet can break rocks effectively by taking advantage of the water hammer effect, and is thus widely used in mining, petroleum, and natural gas fields. With the aim to further clarify the flow field characteristics of pulsed jets induced by a Helmholtz oscillator, large eddy simulation was conducted under different operating pressures. The velocity distribution, mean flow field, and the coherent structure were examined using the oscillators of different cavity lengths and diameters. The results clearly showed that the major frequency of jet pulsation gradually increased with the increase of operating pressure. A stable periodic velocity core was formed at the outlet of the Helmholtz oscillator, while the external flow field was subjected to periodic impact. As a result, the ambient fluid was strongly entrained into the jet beam. With the increase of the cavity length, the length of the core segment decreased while the energy loss caused by the cavity increased, which was also accompanied by a rapid attenuation of the axial velocity at the jet outlet. The coherent structure of the jet in the oscillator with small cavity diameter was more disordered near the nozzle outlet, and the vortex scale was larger. The effect of cavity diameter can be reflected in the feedback modulation of the jet in the cavity. Compared with the conical nozzle, the length of the core section of the jet was shorter, but the jet had better bunching, a smaller diffusion angle, and better mixing performance. These results provide a further understanding of the characteristics of pulsed water jet for better utilizations in the fields of energy exploitation.

Experimental investigation on the rock erosion characteristics of a self-excited oscillation pulsed supercritical CO2 jet

Supercritical CO2 (SC-CO2) jet is now widely considered to have great potential for application in oil-gas exploration and development. In order to further improve the performance of SC-CO2 jet, the rock erosion characteristics of a self-excited oscillation pulsed SC-CO2 jet (SOPSJ) were preliminarily analyzed and then experimentally studied as a pioneering effort. A Helmholtz oscillation nozzle was employed to generate a SOPSJ. Numerous rock erosion tests were conducted. Rock erosion area and depth, erosion intensity evaluated by mass loss, and erosion rate were applied to characterize the erosion performance of a SOPSJ. Results show that unlike the continuous SC-CO2 jets, the erosion areas caused by the SOPSJs are almost unchanged at first and then decrease slowly with the growing standoff distance, while the erosion depths increase first and then decrease. The erosion pits caused by the SOPSJs are relatively large, shallow, and irregular, especially at the initial several standoff distances. Moreover, the SOPSJs can cause larger mass losses than the continuous jets, but this only happens at the initial several standoff distances. The SOPSJs generated with the use of the optimum chamber lengths can maximally enhance the mass loss by about 32.3%, 27.7%, 21.5%, and 17.3% at inlet pressures of 25, 30, 35, and 40 MPa, respectively. In addition, for all the jets, the erosion rates always remain the tendency to decrease with the increase of erosion time. Whereas, the specimens can be eroded by the SOPSJs at a higher rate than the continuous jets, which is independent of the inlet pressure.

Experimental investigation on the impingement characteristics of a self-excited oscillation pulsed supercritical carbon dioxide jet

Supercritical carbon dioxide (SC-CO2) jet is now widely considered to have good potential for use in the field of oil–gas exploration and development due to the unique natural properties of SC-CO2 fluid, and because it offers many advantages over a water jet in various applications. In order to take better advantage of the SC-CO2 jet, a jet-driven Helmholtz oscillation nozzle was applied to produce a self-excited oscillation pulsed SC-CO2 jet (SOPSJ). The impingement characteristics of the SOPSJ were investigated experimentally with respect to the impinging pressure oscillation peak and amplitude, as well as the oscillating frequency. A preliminary theoretical exploration of the relationship between the oscillation characteristics and the unique properties of the SC-CO2 fluid was performed. Numerous impinging pressure tests were conducted with the use of different chamber lengths of Helmholtz nozzle under inlet pressures of 25, 30, 35 and 40 MPa, ambient pressures of 10 MPa, and fluid temperature of 330 K. The results show that compared with the continuous jet the SOPSJ has a greater impinging pressure peak. However, this only happens within a relatively small range of standoff distance depending on the chamber length and the inlet pressure. The maximum peaks are approximately 1.33, 1.29, 1.25 and 1.19 times those of the continuous jets corresponding to inlet pressures of 25, 30, 35, and 40 MPa, respectively. Moreover, the optimal chamber length for obtaining the maximum impinging pressure oscillation peak always leads to the largest amplitude under each inlet pressure. However, this is not true for the other chamber lengths that deviate from the optimal one. In addition, the increase in inlet pressure can cause relatively high dominant frequencies, and the frequency distribution range of the SOPSJ is close to that of the pulsed air–water jet but far from that of the self-excited oscillation pulsed water jet (SOPWJ).

Experimental study on characteristics of self-excited oscillation pulsed water jet

To promote the application of self-excited oscillation pulsed water jet in various fields, various characteristics of self-excited oscillation pulsed water jet were studied experimentally. A test system of self-excited oscillation pulsed water jet characteristics was designed, and it is composed of pulsed jet producer devices, particle image velocity (PIV) measuring system, pressure pulse test device and the confining pressure cavity suitable for a PIV test. The characteristics of flow field, pressure oscillation, pulsed cavitation and acoustic shock of pulsed jet were researched. The results showed that the axis velocity vector at nozzle outlet changes periodically, and gradually becomes smaller away from the nozzle. The peak pressure of self-excited oscillation pulsed water jet is 2.5 times higher than the common continuous jet. The wave crest and the wave trough of pulsed jet are not completely symmetric. As the pump pressure increases, the length of bubble cloud increases, and it first increases and then decreases with confining pressure increasing. The vibration acceleration of sonic boom increases and then decreases as pump pressure increases, and decreases steadily with confining pressure increasing.

Experimental Study on Dynamic Characteristics of Self-Excited Oscillation Pulsed Jet

The dynamic characteristics of the self-excited oscillation pulsed jet is tested by using pulsed jet impact variable cross-section beam in submerged conditions and make comparison with continuous jet, analyzing the effects of operating parameters and nozzle structure parameters on the dynamic characteristics of the pulsed jet. The result show that the oscillating frequency of jet decreases with the increase of cavity length while increases with the increase of the pump pressure. The energy of pulsed jet has obvious change with different cavity length.

Oscillation Mechanism Analysis and Numerical Simulation for Tandem Self-Excited Oscillation Pulsed Jet Nozzle

Self-excited oscillation pulsed jet is the new jet which is superior to the traditional continuous jet. In view of the insufficiency of the widely used organ pipe and Helmholtz resonator at present, firstly, with the actual needs of production as the background, a tandem Self-excited oscillation pulsed jet nozzles is presented in this paper. Then on the basis of previous studies, some new ideas are put forward after the cavity Self-excited oscillation mechanism is analyzed theoretically. Finally, numerical simulation of the nozzle flow field is carried out using FLUENT, then ideal pressure distribution contours and the streamline of the flow field are got, verifying the analysis of the oscillation mechanism.

The influence of collapse wall on self-excited oscillation pulsed jet nozzle performance

The self-excited oscillation pulsed jet (SOPJ) is widely used owing to its simple structure and good separation of pressure source and system. The structure of nozzle is one of the main factors that influence the performance of the SOPJ nozzle. Upper collapse wall and lower collapse wall is important to the formation and transmission of eddy in oscillation cavity. In this paper, the influence of collapse wall on SOPJ nozzle was analyzed by numerical simulation. The LES algorithm was used to simulate the flow of different combinations of collapse wall. The result showed that when both collapse walls are of the same type, the SOPJ nozzle will have a good performance; the influence of upper collapse wall is more obvious than lower one; model of two-semi-circle upper collapse wall is the first choice when we design SOPJ nozzle.

Study on the Relation between Oscillation Frequency of Self-Excited Oscillation Pulsed Water Jet and Self-Excited Pulsed Water Jet Devices

Depending on different structure characteristic of nozzle (self-excited oscillation chamber and special boundary condition), the self-excited pulsed water jet can be produced,which can increase the jet pressure and having the cavitation phenomenon. So,it has been applied in oil driven well、mining and building etc.To study the relation among the frequency of the jetting peak pressure,the peak pressure of the plused-jetting and the self-excited pulsed water jet device,based on the theory of fluid network,the mathematical model of the self-excited oscillation pulsed water jet device was established and the dynamic characteristics parameters of the self-excited oscillation pulsed water jet were tested, which shows that the frequency of the self-excited oscillation nozzle depend on the structure parameter and the dynamic state characteristic of the fluid decisive .the frequency of the jetting peak pressure depends on natural frequency and damping ratio of the device.The experiment proves that the frequency of the jetting peak pressure decreases with the length of the self-excited oscillation chamber,increases with the rising of the pump pressure and there is an optimal length of the oscillation chamber corresponding to the jetting surge pressure. lastly, it clearly shows that the device has functions of oscillator and low pass filter and the jetting peak pressure is the highest when the jet dominant frequency close to the natural frequency of the device. The experimental results help to theory analyzing how to improve peak pressure of the self-excited oscillation jet and have some value in engineering.

Study on the Frequency Characteristic of Self-Excited Oscillation Pulsed Water Jet

The self-excited oscillation pulsed water jet (SEOP Jet ) has been used extensively in oil and gas well drilling, mineral mining, cutting and industrial cleaning. In order to improve the valid stand-off distance of water jet pressure and its range of action, the model of oscillation frequency of jet was given on the basis of hydroacoustics and fluid dynamics for better understanding the principle of increasing jet pressure amplitude. The SD150test system was used to analyze the effects of dynamic parameters on the frequency, the effects of pump pressure and the cavity length on the frequency were studied in detail. The test results showed that the peak value of the SEOP Jet is larger by about 20% than that of continuous jet. The oscillation frequency increased while increasing pump pressure and decreased while increasing cavity length. There was an optimum cavity length corresponding to the pressure peak value of the SEOP Jet. Experimental result is in good agreement with that of theoretical analysis.

Study on improving performance of airlift device by self-excited oscillation pulsed jet used in mining under water

The feasibility of the nozzle of self-excited oscillation pulsed jet (SEOPJ) as the breaker and loosing device for the air-lift pump was researched. The dynamic characteristics of the SEOPJ to crush the hard clay and loose the layer of ore deposit were explored experimentally under the submerged condition. The results show that the SEOPJ not only effectively breaks the hard clay or loose the particles of sand on the placer bed, but also produces fluctuating uplift force acting on particles of sand. The oscillating cross flow caused by the SEOPJ makes particles of sand move to the end of the suction pipe easily. Energy efficency of the airlift and concentration of the solids for the solid-liquid mixture sucked by the air-lift pump are increased obviously with the breaker of SEOPJ.

Theory and experimental study of the self-excited oscillation pulsed jet nozzle

Theory and experimental study of the self-excited oscillation pulsed jet nozzle