Detached eddy simulation on the structure of swirling jet flow field

The improved delayed detached eddy simulation method with shear stress transport model was used to analyze the evolution of vortex structure,velocity and pressure fields of swirling jet.The influence of nozzle pressure drop on vortex structure development and turbulence pulsation was investigated.The development of vortex structure could be divided into three stages:Kelvin-Helmholtz(K-H)instability,transition stage and swirling flow instability.Swirling flow could significantly enhance radial turbulence pulsation and increase diffusion angle.At the downstream of the jet flow,turbulence pulsation dissipation was the main reason for jet velocity attenuation.With the increase of pressure drop,the jet velocity,pulsation amplitude and the symmetry of velocity distribution increased correspondingly.Meanwhile the pressure pulsation along with the axis and vortex transport intensity also increased significantly.When the jet distance exceeded about 9 times the dimensionless jet distance,the impact distance of swirling jet could not be improved effectively by increasing the pressure drop.However,it could effectively increase the swirl intensity and jet diffusion angle.The swirling jet is more suitable for radial horizontal drilling with large hole size,coalbed methane horizontal well cavity completion and roadway drilling and pressure relief,etc.

STUDIES ON STABILITY AND DYNAMICS OF A SWIRLING JET

The temporal instability and nonlinear evolution of the swirling jet near a nozzle exit are studied by both normal-mode method and three dimensional direct numerical simulation (3D DNS),. It is found that the swirl enhances the maximum linear growth rates for negative helical modes, while decreases the growth rate for axisymmetric mode. Numerical simulations show that the evolution in early stage is compared well with the linear stability theory. In nonlinear stage, the swirl promotes the breakup of 3D large scale organized structures in the flow into small eddies.

A Study of the Rock Breaking Mechanism during Swirling Water Jet Drilling

Based on an analysis of the factors affecting rock breaking and the coupling between rock and fluid during water jet drilling, the rock damage model and the damage-coupling model suitable for the whole rock breaking process under the water jet is established with continuous damage mechanics and micro-damage mechanics. The evolvement of rock damage during swirling water jet drilling is simulated on a nonlinear FEM and dynamic rock damage model, and a decoupled method is used to analyze the rock damage. The numerical results agree with the test results to a high degree, which shows the rock breaking ability of the swirling water jet is strong. This is because the jet particle velocity of the swirling water jet is three-dimensional, and its rock-breaking manner mainly has a slopping impact. Thus, the interference from returning fluid is less. All these aspects make it easy to draw and shear the rock surface. The rock breaking process is to break out an annular on the rock surface first, and then the annular develops quickly in both the radial and axial directions, the last part of the rock broken hole bottom is a protruding awl. The advantage of the swirling water jet breaking rock is the heavy breaking efficiency,large breaking area and less energy used to break rock per unite volume, so the swirling water jet can drill in a hole of a large diameter.

THEORETICAL AND EXPERIMENTAL STUDY ON THE CONICAL SWIRLING WATER JET FLOW

This paper is concerned with theoretical and experimental study on the conical swirling water jet flow. Based upon the theoretical analysis, the experiment on the structural characteristics of swirling water jet flow including the velocity and pressure distribution laws, on which the parameters of the jet, nozzle and directional blades have more or less influence, was carried out in CSSRC by using a 3-D LDV in order to optimize a new high-efficiency jet instead of swirling drilling bit for rock-breaking and continuously drilling, and to meet the demand of radial horizontal drilling technology. Meanwhile based on the experimental results, the numerical simulation was conducted for the conical swirling water jet in the immersed well-bottom flow by solving the RANS equations in the 3-D body-fitted coordinate system with the k-e. turbulence model. The numerical results are consistent with the experimental data, and lead to some conclusions which are important for applying the conical swirling water jet to the petroleum drilling engineering.