Study On The Influence Of Low-pressure Environmental On The Hydrodynamic Pressure And The Trajectory Distance Of Jet

With the rapid development of high dam construction in China,many new challenges have emerged,among which the study of high-speed water flow characteristics under low pressure environment in the western region is of great significance to the construction of dams in the plateau,and the high speed water flow aerated tongue is the most critical link in the study of high speed water flow characteristics.This paper studies the main hydrodynamic characteristics of flood discharge system at high altitude and high head,quantitatively analyzes the influence degree of environmental pressure on the mechanical characteristics of high speed water flow,and provides theoretical reference and practical suggestions for the hydraulic design of high altitude and high head flood discharge system,so as to ensure the safety of flood discharge of high altitude special dam to the greatest extent.At the same time,the theory and method system of dam discharge energy dissipation technology are further improved.In this paper,the effect of environmental pressure change on the distance of aerated water tongue is studied by means of model test,and the related hydraulics characteristics of water cushion pond are studied,which provides technical guidance for dam construction in high altitude area.The main results and conclusions are as follows:1.Both the mean pressure and the pulsating pressure peak in the jet impact zone,and there are obvious pressure gradients on both sides.While reducing the air density and air resistance,the average pressure and pulsating pressure in the impact zone of the water cushion pond increase to different degrees.The pressure decreases by 10 kPa,the maximum pressure can reach up to 3.9%,the pulsating pressure can reach up to 5.5%.2.The distribution law of pulsating pressure in frequency domain under different air pressure is basically similar,and the dominant frequency is located in the low frequency segment.The width of the frequency band at low pressure is wider than that at normal pressure,and the frequency increases,which indicates that the decompression causes the increase of small-scale vortices and the proportion of small-scale vortices in various scale vortices increases3.The trajectory distance of jet is affected by the aeration and diffusion of the jet flow in the air.Due to the similarity law between the model and the prototype,the influence of air resistance on the water tongue spacing is different in the model and the prototype.However,with the decrease of environmental pressure,air density and air resistance,the air entrapped by the water tongue in the air will also be reduced,that is,the diffusion degree of the water tongue will be reduced,and the low pressure water tongue will be more concentrated.