回流式自激振荡器脉冲流动特性数值研究

Numerical Study on Pulse Flow Characteristics of Reflux Self-excited Oscillator

自激振荡器产生的脉动射流会对钻柱起到激励振动作用,将钻柱与井壁的静摩擦转化为动摩擦,实现动态减阻。对于井下作业高围压、大流量工况,为使自激振荡器所产生的脉动射流频率进一步降低,在前人研究的基础上,结合附壁射流效应、涡激振动效应以及流体反馈作用,提出了高围压低频回流式自激振荡器,并利用CFD方法分析了振荡器内部脉冲流动特性。分析结果表明:由于附壁流动、漩涡推动、圆柱绕流以及碰撞反馈,造成主射流在振荡腔内来回摆动、出口射流脉动;随着圆柱形整流块半径增大,频率先增大后减小;回流通道宽度超过一定值,频率变化不明显;随着振荡腔长度增加,频率单调减小;随前振荡壁夹角增大,脉动射流频率存在极小值。研究结果可为振荡器脉冲频率调节及新型自激振荡器开发提供参考。

The pulse jet produced by self-excited oscillator excites and vibrates the drill string and converts the static friction between drill string and borehole wall into the dynamic friction,reducing the friction dynamically.In order to reduce the frequency of pulse jet produced by self-excited oscillator under the downhole conditions of high confining pressure and large flow rate,a reflux self-excited oscillator with high confining pressure and low frequency was presented based on previous studies,considering the wall-attached jet effect,vortex-induced vibration effect and fluid feedback effect.In addition,the CFD method was used to analyze the flow characteristics of pulse in the oscillator.The analysis results show that the wall-attached flow,vortex push,circular cylinder and collision feedback make the main jet swing back and forth in the oscillating cavity,leading to the outlet jet pulse.As the radius of the cylinder rectifier block increases,the frequency increases first and then decreases.When the width of reflux passage exceeds a certain value,the frequency does not change obviously.As the length of the oscillating cavity increases,the frequency reduces monotonically.As the angle of the front oscillating wall increases,the frequency of pulse jet has a minimum value.The results provide references for the adjustment of oscillator pulse frequency and the development of new self-excited oscillators.