实验可压缩流动实验笔记的写法

Notes for Experiments - Compressible Flow Experiment

实验可压缩流动实验笔记

 

Objectives目标

 

 

(1) To study the compressible flow of air in a convergent-divergent nozzle under different pressuredifferentials between the inlet and outlet.在可压缩的空气流量测验中，研究了在收敛扩散形喷嘴在不同的入口和出口之间的压力差。(2) To study the effect of choking on the mass flow rate through a convergent-divergent nozzle.(3) To study the formation of shock waves in the divergent section and changes in pressure acrossthem.(4) To study the streamwise pressure variation in the convergent-divergent nozzle.(5) To compare the experimental results with theory.用来比较不同的实验结果与理论。

 

 

Apparatus设备

 

 

The nozzle, supply pressure valve, back pressure valve, orifice plate and the manometer;Thermometers; Barometer.

喷嘴供给压力阀，背压阀，孔板和压力计，温度计，气压计。

 

Theory理论

 

 

To accelerate a gas at rest to supersonicspeeds, it is essential that the gas isaccelerated subsonically in a convergentduct first, and then further expanded tosupersonic speeds by diverging the duct.处于静止状态，以超音速的速度加速气体的流动，这是必不可少的一个步骤，气体被加速时所产生的亚音速在收敛导管占据着第一位的因素，完成这个步骤之后以超音速的速度来进一步扩大所述的发散管道。Hence, a nozzle designed to achievesupersonic flow at its exit is a convergent-divergent duct. Since the Mach number atthe throat cannot exceed 1, the mass flowremains constant when pressure at thenozzle exit is further reduced. This is thesituation of choked nozzle flow. When thenozzle is operating at the pressure ratio forwhich it is designed no shock waves will beformed. When the outlet pressure is abovethe design value, a shock wave will beformed, accompanied by flow deceleration.

 

  当出口压力高于设计值，将形成冲击波，并伴随着气流而减速。

Experimental Tests实验测试

 

 

(1) Experiment 1: Variations of mass flow rate with back pressure for constant supply pressure.实验1：稳定供应的质量流量与背压变化之间的压力。(2) Experiment 2: Variations of streamwise pressure within the nozzle for given supply pressure anddifferent back pressure.

 

 

Experimental Procedure实验步骤

 

 

Experiment 1: Fixing the supply pressure and changing the back pressure固定的供给压力，并改变背压

(a) Open fully both the supply pressure valve and the back pressure valve;(b) Bring down the static pressure probe fully so that it measures the back pressure;(c) Set the supply pressure to 500 kPa by adjusting the supply pressure valve, and read the water levelon the manometer;(http://www.ukassignment.org/dxessay/) Vary the back pressure by adjusting the back pressure valve: Increase the back pressure step bystep until the back pressure becomes equal to the supply pressure. At each step read the waterlevel in the inclined manometer.在每一步中读取倾斜压力计内的水位。

Experiment 2: Measuring variations of streamwise static pressure along the nozzle axis

This experiment should be carried out for two supply pressure P0. For each supply pressure anumber of back pressures should be set. Choose the back pressure such that the results cover variousregimes: (a) subsonic throughout; (b) subsonic sonic (at throat) supersonic shock subsonic;or (c) subsonic sonic supersonic (design condition).The procedure is the same as in Experiment 1, but at each step, instead of reading the water levelin the manometer, traverse the probe across the nozzle and read the pressure within the nozzle from thegauge.

 

 

Important Notes重要注意事项

 

 

(1) The pressures measured are gauge pressures and therefore the absolute values have to becalculated. 测得的压力是表压，因此，必须计算的绝对值。A barometer will provide the atmospheric pressure (or you can take Pa51.0132510as the ambient pressure).(2) The scale on the manometer is already calibrated and thus it gives the water height in inches ofwater.(3) When the probe is fully inserted, you must take into account the reduction in the throat area due tothe presence of the probe.当探针完全插入时，则必须考虑到减少由于探针的存在所出现的喉部面积。

 

Parameters to be Measured测量的参数

 

Supply pressure in the reservoir P0在水库P0供应压力; Back pressure;Temperature of air in the reservoir T0; Temperature of air as it leaves the pipe downstream of theorifice plate in order to obtain the air density for the calculation of mass flow rate through the orificeplate;Water level in the manometer in Experiment 1 that leads to the calculation of mass flow ratethrough the nozzle using the orifice plate relation.

 

 

Analysis Required需求分析

 

(1) Variations of mass flow rate with back pressure (Experiment 1).(2) Variations of pressure in the nozzle for different supply pressures and back pressures, in the formP/P0vs. position in the nozzle (Experiment 2).(3) Theoretical computation of the maximum mass flow rate for given supply pressure andcomparison with the experimental value (Experiment 1).对于给定的供给压力，与实验值（实验1）计算的最大质量流量的理论来进行对比。