超音速喷嘴仿真

from parallel. A matching pair concave mirror catches the light once it has gone through the nozzle and refocuses it onto a knife edge. The knife edge is set to allow about ½ of the light beam through to a viewing screen or camera. Light bent by expansions will be stopped at the knife edge. This missing light will cause dark areas on the screen where expansion waves occur. Light bent by compressions (shocks) will completely pass the knife edge and hence brighten these areas on the screen. The system can thus be used to produce images of supersonic flow. Experimental Procedure Note : If you do not have access to a supersonic nozzle and a high pressure gas line, use the Nozzle Simulation software program to carry out your experimental investigations. 1. With an empty test section, open the control valve and establish supersonic flow in the channel. Measure the static pressure readings along the length of the nozzle. Measure the total pressure reading for the upstream flow. Measure the atmospheric pressure in the lab. Recorded data can be written in the tables shown in the Appendix. 2. A pitot pressure probe can be inserted into the flow to measure stagnation pressure behind a normal shock wave. This is another technique for measuring the Mach number of the flow in the nozzle. Record the Stagnation pressure using the probe at station 6 in the nozzle. 3. With glass walls on the side of the nozzle and by means of a Schlieren optical system, the shock/expansion wave system produced by objects placed in the flow can be seen. These flow patterns can be recorded digitally. Install a test shape into the test section of the channel. Again open the valve to establish supersonic flow. Record the shock and expansion wave patterns using the Schlieren optical system. 4. With an otherwise empty test section, if small step disturbances are introduced at the walls, the resulting weak Mach waves can be observed by the optical system. The angle of these waves will be another measure of the Mach number of the flow in the nozzle. Experimental Results
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ｈ ｃ ｅ
ｏ －ｄ
ｉ ａ ｍ
． ｎ
ｍ ｏ ｃ
Figure 2. High Pressure Supply System.
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． ｗ
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ｈ ｃΒιβλιοθήκη ｏ ｄ －ａ ｍｎ ｉ
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Figure 3. Schematic of Equipment Connections.
Nozzle Geometry Nozzle stations are measured downstream from the throat. Table 1. Nozzle Co-ordinates
Figure 1. 2-D Supersonic Flow Nozzle Experimental Procedure.
Observe the set up of the apparatus, Figure 2. Take note of each piece of equipment and its function. The high-pressure gas supply line is attached via a manually operated valve to the converging-diverging two-dimensional nozzle. Once the valve is open to give sufficient upstream stagnation pressure, the nozzle will choke giving Mach 1 flow at the throat. Downstream of the throat (area A*) the flow Mach number will depend primarily on the area ratio of the channel (A/A*) and a supersonic flow slightly above Mach 2 will be obtained. A steel wall containing static pressure ports can be attached to the side of the nozzle. Using these ports, static pressure variation along the nozzle length can be determined. The static pressure to stagnation pressure ratio at any point along the channel can be used to predict local Mach number. This result can be compared to area ratio predictions and discrepancies due to boundary layer effects, shock waves or surface imperfections can be evaluated. A pitot pressure probe can be inserted into the flow at any station and can be used to predict upstream Mach number based on the stagnation pressure ratio change at that station.
P= P atm − hi
cmHg
Figure 5. Static Pressure Multitube Manometer
Optical Measurement of Shock and Expansion Waves
A Schleiren optical system is set up in the lab surrounding the nozzle.
Measurements in Supersonic Flow
The aim of this laboratory experiment is to familiarise students with the behaviour of supersonic gas flow. To complete the work successfully students will need to understand the properties of supersonic flow as well as equipment and techniques required to perform measurement of this flow.
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Throat Height (A*) = 14.5 mm. Nozzle is two-dimensional with a constant depth, 25.4 mm Pressure measurement Pressure measurement can be carried out using Piezo-electric transducers or conventional manometers. In this case mercury manometers are used to measure the pressures in the nozzle or upstream reservoir. Stagnation pressure is taken as measure as the static pressure of the upstream settling chamber. Since the stagnation pressure in the upstream pressure vessel is quite high, a multicolumn manometer has been used rather than one very long single column. The mercury columns are joined by incompressible water columns.