近年来随着城市居住人口数量的不断增长，市政排水系统所承受的压力与日俱增，加之市政排水管网设计规划时期早，投入使用年头长，使得因管道污垢引起的管网淤堵冒溢和水环境污染等城市问题尤为突出。为了解决此类水问题，许多城市开始针对老城区的市政污水管网进行维修改造，然而市政管网多铺设于地下，如果把所有淤堵的管道全部更换，不仅维修成本高还会大面积破坏路面，因此管道污垢清洗将成为解决城市管网系统淤堵冒溢的主要途径，寻求高效、环保的管道清洗方法至关重要。
为此本文针对高压水射流技术清洗管道污垢的应用，通过理论分析、模型试验和数值模拟相结合的方法进行系统性研究，具体内容如下：
首先，开展高压水射流技术清洗管道结垢层的理论研究，对流体力学基本理论进行了详细阐述，明确了高压水射流的流态为典型的紊流，水射流的类型主要分为连续射流、脉冲射流和空化射流，水射流的结构可分为初始段、基本段和消散段。通过基础理论研究的结果，对水射流的清洗工艺参数进行设计，主要包括喷嘴结构几何参数及射流工作参数，水射流的工作参数包括水射流速度、流量、功率以及水射流反冲力的计算公式，并推导了水射流冲击力的计算方法，提出了水射流的清洗机理，包括结垢层破碎机理及结垢层切削机理。
其次，根据实际工程案例和场地条件建立了高压水射流管道清洗水力模型试验系统，针对管道结垢层进行了清洗试验，选取了4种不同管径的管道作为研究对象，研究水压、入射角度、靶距以及管径4个因素对管道清洗效果的影响。观测清洗过程中水射流流态变化并结合管道结垢层去除率分析，获得了以下结论：高压水射流清洗管道结垢层可分为冲孔阶段、结垢层裂隙出现阶段、结垢层裂隙发展阶段和结垢层剥离阶段。射流水压增大会增强清洗效果，入射角度和靶距的变化对清洗效果有影响。管道管径的改变主要影响了反射后水流对结垢层的切削作用。由于射流靶面为凹面，射流冲击力不仅仅表现为竖直向的穿孔力还有水平向的切削力，随水压的增大，穿孔力和切削力均增大；射流入射角度增大时，穿孔力增大但切削力减小；靶距增大时，穿孔力和切削力均下降。并且通过试验获得了清洗管道结垢层的最优参数组合，当水压为16MPa时结合用水量分析，此时管道结垢层去除率达42%的最优水平；当水射流入射角为45°时，射流冲击力横向切削和竖向穿孔达到平衡，管道结垢层去除率达100%；射流靶距为100mm时，随着射流冲击面积的增大，结垢层去除率达到了38%。
再次，基于 Realizable k-ε 湍流模型和 VOF 多相流模型建立了高压水射流清洗气-水两相流三维数值模型，研究了水射流冲击管壁反射后的流速场以及水射流冲击靶面的压强场随上述四个参数变化而变化的规律，以弥补物理试验的局限性。其中，射流流速场研究射流冲击管壁后发生发射形成扇面流体的流速分布，靶面流速在实际清洗中可以代表水射流对结垢层切削作用的效率；射流压强场研究水射流冲击到管壁时的靶面压强，靶面压强在实际清洗中表示水射流对结垢层表面穿孔作用的效率，通过分析模拟试验数据并与物理试验结果相联合分析后得到：当水压增大时，射流速度场及压强场均随之增大，水射流对结垢层的切削与穿孔作用均增强；入射角度增大时，射流速度场减小，而压强场增大，水射流对结垢层的切削作用增强但穿孔作用减弱；靶距增大时，射流速度场及压强场均有不同程度减小，但直接清洗面积增大，水射流对结垢层的切削与穿孔作用均减弱；管径增大时，会使射流速度场减小，而压强场几乎不受影响，水射流对结垢层的切削作用增强而穿孔作用无变化。
高压水射流清洗模型的气-水两相流动特性及除垢机理研究结果对其关键参数设计与选取提供充分的理论依据，能够为市政污水管网系统安全运营提供技术保障。

In recent years, with the continuous growth of urban resident population, the municipal drainage system has been under increasing pressure. In addition, the municipal drainage network has been designed and planned early and put into use for a long time, which makes urban problems such as pipe network blockage and overflow and water environment pollution caused by pipeline dirt particularly prominent. In order to solve this kind of water problem, many cities began to repair and transform the municipal sewage pipe network in the old city, but the municipal pipe network is mostly laid underground, if all the silted pipes are replaced, not only the maintenance cost is high, but also the road surface will be destroyed in a large area, so the pipeline dirt cleaning will become the main way to solve the congestion and overflow of the urban pipe network system. It is important to find efficient and environmentally friendly pipe cleaning methods.
Therefore, aiming at the application of high-pressure water jet technology to clean pipeline dirt, this paper conducts a systematic study through the combination of theoretical analysis, model test and numerical simulation. The specific contents are as follows:
First of all, the theoretical research of high-pressure water jet technology to clean the scale layer of the pipeline is carried out, and the basic theory of convection mechanics is elaborated. It is clear that the flow state of high-pressure water jet is typical turbulent flow, and the types of water jet are mainly divided into continuous jet, pulse jet and cavitation jet, and the structure of water jet can be divided into initial section, basic section and dissipation section. Based on the results of basic theoretical research, the cleaning process parameters of water jet are designed, which mainly include nozzle structure geometric parameters and jet working parameters. The working parameters of water jet include the calculation formula of water jet velocity, flow rate, power and water jet recoil force. The calculation method of water jet impact force is derived, and the cleaning mechanism of water jet is proposed. It includes the breaking mechanism of scale layer and cutting mechanism of scale layer.
Secondly, a hydraulic model test system for high-pressure water jet pipeline cleaning was established according to actual engineering cases and site conditions. The cleaning test was carried out for the scale layer of the pipeline. Four kinds of pipelines with different pipe diameters were selected as research objects to study the influence of four factors, namely water pressure, incident Angle, target distance and pipe diameter, on the cleaning effect of the pipeline. Based on the observation of the change of water jet flow pattern in the cleaning process and the analysis of the removal rate of scale layer, the following conclusions are obtained: the cleaning of scale layer by high pressure water jet can be divided into punching stage, the appearing stage of scale layer crack, the developing stage of scale layer crack and the stripping stage of scale layer. The increase of jet water pressure will enhance the cleaning effect, and the change of incident Angle and target distance will affect the cleaning effect. The change of pipe diameter mainly affects the cutting effect of reflected water flow on the scale layer. Because the target surface of the jet is concave, the impact force of the jet is not only manifested as the vertical piercing force but also the horizontal cutting force. With the increase of water pressure, both the piercing force and the cutting force increase. When the jet incidence Angle increases, the perforating force increases but the cutting force decreases. The piercing force and cutting force both decrease when the target distance increases. The optimal parameter combination of cleaning pipe fouling layer is obtained through the test. When the water pressure is 16MPa combined with the analysis of water consumption, the removal rate of pipe fouling layer reaches the optimal level of 42%. When the incidence Angle of water jet is 45°, the balance between transverse cutting and vertical perforation of jet impact force is achieved, and the removal rate of scale layer reaches 100%. When the jet target distance is 100mm, the scale removal rate reaches 38% with the increase of jet impact area.
Thirdly, a three-dimensional numerical model of high-pressure water jet cleaning gas-water two-phase flow was established based on k-ε model and VOF multiphase flow model. The velocity field after water jet impact on pipe wall and the pressure field of water jet impact on target surface were studied with the changes of the above four parameters, so as to make up for the limitations of physical tests. Among them, the flow velocity field studies the flow velocity distribution of the fluid on the fan surface formed by the emission after the jet impinges on the pipe wall, and the flow velocity on the target surface can represent the cutting efficiency of the water jet on the scale layer in actual cleaning. The target surface pressure field is studied when water jet impacts the pipe wall. The target surface pressure represents the efficiency of water jet perforating the surface of the scale layer in actual cleaning. Through the analysis of the simulation test data and the combined analysis with the physical test results, it is concluded that when the water pressure increases, the jet velocity field and pressure field increase, and the cutting and perforating effects of water jet on the scale layer are enhanced. When the incidence Angle increases, the jet velocity field decreases, and the pressure field increases, the cutting effect of water jet on the scale layer is enhanced, but the perforation effect is weakened. When the target distance increases, the velocity field and pressure field of the jet decrease to varying degrees, but the direct cleaning area increases, and the cutting and perforating effect of the water jet on the scale layer decreases. When the diameter of the pipe increases, the velocity field of the jet decreases, but the pressure field is almost unaffected. The cutting effect of the water jet on the scale layer is enhanced, but the perforation effect does not change.
The research results of gas-water two-phase flow characteristics and descale mechanism of high-pressure water jet cleaning model provide sufficient theoretical basis for the design and selection of its key parameters, and can provide technical support for the safe operation of municipal sewage pipe network system.