The Design And Numerical Simulation Research Of Downhole Centrifugal Supercharging System

In order to meet the requirement of high-pressure water jet drilling technology, a downhole centrifugal supercharging system, which consists of turbo-power unit, fluid-solid centrifugal separating unit, centrifugal supercharging unit and double flow channels unit, is present in this thesis. Turbine is drived by the drilling fluid which propels both the fluid-solid separating unit and the centrifugal supercharging unit. Clean drilling fluid from the separating unit is supercharged and enters the high-pressure flow channel and in the end, the high-pressure nozzle in the bit which increases the bottomhole jet pressure and velocity, and moreover, increases the drilling rate and lowers the drilling cost.Based on the analyses of traditional blade molded lines, with the core of optimizing the turbine blade molded lines in mind, a new design method for the high-speed turbine blades molding is present in this thesis with the characteristics of molded line models up to continuous three-order derivatives, avoidance of the flow separation near the rear of the blades, smooth changes of the velocity and pressure on the blade surface and high efficiency of the turbine. Moreover, numerical simulation is performed on the internal flow inside the turbine motor with Reynolds-averaged equations and modified RNGk ?εturbulence model which eliminates the leakage problem and optimizes the high-speed turbine design.On the basis of previous analyses of complex structure of the multistage high-speed centrifugal pump, a new method combining Visual Basic and Pro/Engineer is present applying the Beizer curve to the parametric design of multistage high-speed centrifugal pump blades and a CAD software is also released. A high-speed centrifugal pump with 112 stages is created with the CAD software together with the physical condition of drilling engineering.A full three-dimensional numerical simulation of internal flow and bulk performance of a 5-stage centrifugal pump is performed with emphases on the flow details of each stage, for example, the performance of each impeller and pulley, meridian-plane-averaged flow parameters and parameter distributions on three dimensions. Numerical results show that good conformance of flow characteristics is found among the stages except the first stage which proves that computational domain of three stages is enough to reveal the full information needed about the whole prototype.Experimental results fully support the theoretical analysis which shows that under current drilling condition, the centrifugal supercharging system invented in this thesis can produce torque up to 273N.m, output power of 118.8kw and bulk performance of 59.8%. The output pressure increment up to 26.1MPa, the bulk performance of 61.2% and nozzle pressure drop up to 36MPa can achieved with such a centrifugal pump under the condition of 115kw shaft power and 260.95N.m torque, which provides a new technical support for the development of downhole supercharging drilling technology.