Following this experiment, itis evident that the analysis of a simple device like the converging divergingnozzle is more involved than was originally anticipated. For the resultsobtained for the maximum mass flow rates against the back pressure in Figure 6, it is felt that the valuesare counter intuitive and prove to be correct. These results can be used couldbe used safely for non-critical approximations if desired. The second part ofthe lab, measuring the pressure distribution along the axis of the nozzle as afunction of the pressure ratio gave a good indication of the flow patterns thatoccur in the nozzle and how they can be used to achieve desired flows ifnecessary.Conclusion It has to be mentioned that there couldhave been possible errors made by students when reading the manometer (althoughthese are unnecessary mistakes they still need to be mentioned)There possibly may have been errorsthat went unnoticed in the lab with pressure gauges which could account for asmall level of error.One of these errors may be the positivedisplacement of the compressor in the apparatus.
There were minor fluctuationsthat occurred due to its method of operation in load and unload cycles. Evenwith the pressure regulator in the system, it provided the system to smoothenout these fluctuations but there still may be some margin of error present. Avery high level of maintenance and calibration would be necessary to reducethese to a certain extent. It was felt after the conclusion of theexperiment that a number of factors could have caused discrepancies between the results of the experiment.Experimental ErrorsDuring the experiment, these valueswere recorded in the table given to us in the brief and plotted in Figures 6,7 and 8. To achieve a flowpattern which can be attributed to the design condition, where the supersonic flowat the nozzle exit contains no shock waves and is not chocked at the throat. Theplotted line must decrease smoothly to a value above the unexpanded flowcondition. On examining Figure 7 itis seen that we achieve no value consistent with the design condition.
This canbe attributed to the pressure drop, step size of approximately 50 kPa. The objective of the Compressible Flowlab experiment was to measure the pressure distribution within the nozzle overa range of pressure ratios. In the nozzle, the isentropic expansion of thefluid to a supersonic flow is dependent on the back-pressure ratios applied tothe system. By measuring the linear variation of pressure at different lengthsthrough the nozzle it can be determined from Figures 7 and 8 with whattype of flow is occurring within the system.