柴油机水下排气管口边界模型

A Boundary Model of Submerged Exhaust Exit of Diesel Engine

柴油机废气排入水中所形成的尾管口边界比较复杂。在柴油机水下工况数值模拟中,一般采用定压模型。本文从流体力学的基本方程出发,根据对水下排气管口两相流动状态的观察和管口气泡形成过程的研究,建立了柴油机水下排气不稳定流动管口边界模型。与定压模型相比,该模型不仅能反映出管口的压力波动,而且可以模拟管口处气泡的形成过程及其与管口内气体之间的相互作用。与1维不稳定流动方法相结合可以进行柴油机水下工况的特性分析,特别是水下排气管口声辐射的数值模拟。

The flow at submerged exhaust exit is complex when a diesel engine discharges pulse exhaust gas into water, so that a model of constant pressure has to be used in numerical simulations of underwater performance of diesel engine. In this paper, a theoretical model of unsteady flow at the submerged exhaust exit of diesel engine was established on the base of basic equations of hydrodynamics and observations of TV camera' s replay of two-phase flow pattern as well as investigations of bubble formation at the submerged exhaust exit. Comparing with the constant pressure model, the model enables not only to describe the actual pressure pulsation at the exit, but also to simulate the process of bubble formation at the exit and the interaction of the bubble with the gas inside the exit. Combining with methods of one dimension unsteady flow, the model can be used in analysis of underwater performance, and especially in prediction of sound radiation from the sub- merged exhaust exit of diesel engine.