Research On Flow Coefficient And Dynamic Flow Characteristics For Large Diameter Disc-type Special Valve

The large diameter disc-type special control valve(i.e.,special valve)is one of the main control valves which control the timely temperature and pressure of the air intake system to the temperature and pressure of the flight environment for the altitude test facility.There is a significant difference in the flow coefficient value of the current special valve(with a maximum error of 15%),resulting in poor adjustment performance of the special valve on the altitude test facility.To improve control model precision of the special valve flow coefficient,the flow coefficient and transient flow characteristics were studied based on Fluent software simulation analysis.The effects of 9 openings(10°,20°,30°,40°,50°,60°,70°,80°,and 90°)and 9 pressure ratios(0.1,0.2,0.3,0.4,0.5,0.6,0.7,0.8,and 0.9)on internal velocity,pressure,and flow coefficient of special valves are explored and analyzed on basis of 8 different flow adjustment ranges(0%～100%,0%～92%,0%～72%,0%～64%,0%～44%,0%～36%,0%～16%,and 0%～8%).On this basis,the transient flow characteristics of the special valve were studied through dynamic grid technology between opening and closing processes in 2 s when the pressure ratios of 0.8 and 0.9,and the opening range of 50°～60° and 60°～70°,respectively.The study’s results can provide a theoretical basis for the engineering application of special valves and an accurate flow characteristic model of special valves for the aeroengine altitude test facility.The main researches are as follows:(1)The influences of flow adjustment range,opening degree,and pressure ratio on the flow characteristics of the special valve were analyzed through numerical simulation.The research results show that the velocity and pressure in the special valve were symmetrically distributed along the stepless regulating disk.When the opening and flow adjustment range increases,the airspeed increases gradually.For example,when upstream pressure of the valve was 200 k Pa,the flow adjustment range was 0%～100%,and the pressure ratio was 0.1,the inlet velocity for an opening of 90° was 72.92 m/s,which was about 9 times of the opening of10°.When the opening and flow regulation range was constant,the inlet velocity increases with the pressure ratio first constant and then decreases.On this basis,combined with the pressure difference between the front and rear of the special valve and the speed behind the valve,research and analysis of the change law of the special valve flow resistance coefficient.The results show that the special valve’s flow resistance coefficient decreases with the opening and pressure ratio increase.When the opening was 10°～40°,the flow resistance coefficient decreases most significantly,and when the opening was increased from 10°～20°,the flow resistance coefficient decreases by 91%.(2)Based on the above flow characteristics of special valves,the calculation formula of flow coefficient derived from continuity equation,Bernoulli equation and isentropic process equation is introduced.The relationship between the flow coefficient and the flow regulation range,opening,and pressure ratio was studied and analyzed.The research results show that the flow coefficient was approximately linearly related to the flow regulation range.While keeping the opening degree of the special valve constant,the flow coefficient with the pressure ratio of the changing trend was basically similar.The special valve flow coefficient with the pressure ratio decreases,increases,and then unchanged.There was a critical pressure ratio,and the critical pressure ratio increases with the increase of the flow adjustment range and opening degree.In addition,the flow coefficient increases with the increase of opening degree,for example,when the upstream pressure was 200 k Pa,the flow adjustment range was0%～100%,and the pressure ratio was 0.9,the flow coefficient of opening degree of 90° was0.316,which is about 1.2 times of the flow coefficient of opening degree of 10°.(3)Based on the response time of the altitude test facility special valve test,the study focused on exploring the transient flow characteristics during the opening of the special valve in 2 s,3 s,5 s,and 8 s time.The research results show that the flow resistance coefficient and flow coefficient trends for opening times of 2 s,3 s,5 s,and 8 s were basically similar,and the values of the values for 3 s,5 s,and 8 s were nearly the same.When the opening time was2 s,the special valve flow coefficient relative to 3 s,5 s,and 8 s flow coefficient was small,and the flow resistance coefficient was relatively large.When the opening time was 3 s,5 s,and 8 s,the flow coefficient and flow resistance coefficient of the special valve was basically unchanged at the same opening degree.(4)Based on the transient flow characteristics of different opening times,the flow characteristics of the valve opening and closing within 2 s of 50°～60° and 60°～70° opening under the pressure ratio of 0.8 and 0.9 were studied and analyzed to further reveal the transient flow characteristics of special valves.The research results show that during the opening and closing process of the valve,the pressure distribution law and velocity distribution law were basically consistent.The flow channel in front of the stepless regulating disc was the area where the pressure and velocity change most acutely,and the pressure and velocity stratification was obvious.Due to the changes in the flow channel of the special valve during the closing process,the negative pressure area and the low-speed area of the flow channel in the stepless regulating disc were slightly larger than the negative pressure area and the lowspeed area when the valve was opened.