针栓式喷注器液膜下漏率预估模型

为了对针栓式喷注器液膜下漏率进行准确预测,基于针栓式喷注单元喷雾场结构分析,结合理论推导、数值仿真及试验研究3种方法建立了液膜液束各自变形的相对变形量模型;在考虑液膜液束变形的基础上,引入相互影响系数表征多喷注单元间相互影响,建立了实际阻塞率和实际下漏率模型。通过数值仿真及试验结果的多参数充分验证,结果表明:理论预估模型与数值仿真及试验结果一致性较好。液膜液束相互作用下,液膜绕液束流动和液束根部横截面前后缘位置移动不同步导致的展向变宽分别是液膜和液束发生变形的主因,且有效动量比越大,液膜相对变形越大,液束相对变形越小。对于一定阻塞率的几何结构,结果表明:下漏率随着有效动量比的增大而增大,增大趋势呈先快后缓,且实际下漏率均小于几何下漏率,这是由膜束变形导致的实际阻塞率比几何阻塞率更大造成的。另外,发现液膜下漏率仅与表征流场结构(有效动量比)及几何结构的无量纲参数(液膜厚度与液束直径之比和阻塞率)有关,与喷射速度的绝对值无关,并给出了模型中的常系数供工程设计预估使用,对从设计初期就考虑针栓头的热防护问题具有重要的指导意义。

Prediction model of leakage rate of liquid sheet in pintle injector

In order to predict accurately the leakage rate of liquid sheet in pintle injector,the relative deformation models of a liquid sheet and a liquid jet were established,based on the analysis of a spray field structure of a pintle injector element,and by combining with three methods of theoretical derivation,numerical simulation and experimental research. Taking the deformation of liquid sheet and liquid jet into consideration,the models of actual blocking rate and actual leakage rate were established for the first time by introducing coefficient of interaction to characterize the interaction between multi-injector units. Through multi-parameter verification of the numerical simulation and experimental data,the results showed that the predicted values of theoretical model were consistent with the numerical simulation and experimental data. Under the interaction of liquid sheet and liquid jet,the main causes of the deformation of liquid sheet and liquid jet were respectively a flow of liquid sheet around liquid jet and a transverse broadening of the root section caused by an asynchronous movement of the position of the front and rear edges at the root of liquid jet. Besides,the larger effective momentum ratio meant the greater relative deformation of liquid sheet and the smaller relative deformation of liquid jet. For the geometry structure with a certain blocking rate,the results showed that the leakage rate increased with the increase of the effective momentum ratio,and the increasing trend was fast first and then slow. The actual leakage rate was less than the geometric leakage rate,because the actual blocking rate was larger than the geometric blocking rate due to the deformation of liquid sheet and liquid jet. In addition,it was found that the leakage rate was only related to the dimensionless parameters characterizing the flow field structure (effective momentum ratio) and the geometry structure (ratio of sheet thickness to jet diameter and blocking rate),independent of the absolute value of injection velocity. The constant coefficients in the model were given for the engineering design prediction,providing an important guiding significance for considering the thermal protection of pintle tip in the early stage of design.