This applet simulates a converging-diverging nozzle, a most important element in the fields of propulsion and high speed flow of gases. The user is allowed to "design" a converging-diverging nozzle for analysis by specifying the ratio of the nozzle exit area to throat area, the specific heats ratio of the gas, and the pressure ratio across the nozzle. The applet then computes and displays the pressure, temperature, and Mach number along the nozzle.
Type of Material:
Java Applet calculator.
Classroom demonstrations and homework assignments. May be used to augment lectures on one-dimensional compressible flow. Students may also be assigned homework problem that entail using the calculator to solve problems related to converging-diverging nozzles.
Browser with JAVA support enabled. Some problems encountered when running Netscape 7.1. Details of these problems are discussed below.
Identify Major Learning Goals:
To demonstrate the principles underlying compressible flow through nozzles and to provide a simple model of a nozzle that a student or instructor can use to see the effects of various parameters on nozzle performance.
Target Student Population:
Undergraduate/graduate students taking courses in the areas of gas dynamics or propulsion systems.
Prerequisite Knowledge or Skills:
Basic principles of fluid mechanics and gas dynamics in general and converging-diverging nozzles in particular.
This learning object provides a very useful online calculator that removes much of the tedium normally associated with compressible fluid flow through converging-diverging nozzles. It addresses topics that are difficult to both teach and learn because of the complex equations that describe nozzle flow. It makes very effective use of graphics by displaying the nozzle itself along with curves representing the pressure and Mach number along the nozzle and a colored contour map to display the temperature. Comparing "exported values" from the program with those appearing in standard print publications (e.g., NACA 1135), excellent agreement is found.
Potential Effectiveness as a Teaching Tool
With its excellent graphics and user interactivity, this learning object has high potential effectiveness as a teaching tool. It provides both visualization of concepts and computation of values not easily demonstrated because of the complexity of the equations involved. It eliminates the need to use standard tables that provide isentropic flow values in terms of the flow Mach number. Likewise, the program allows values for the specific heats ratio other than the standard "table" value of 1.4 for air.
One very useful feature is the "Auto Run" which provides an animation showing the effects of varying the nozzle back pressure. The location of the shock wave (a problem of some difficulty if hand calculations are used) and its movement along the nozzle is immediately apparent. The material can certainly be used with any standard textbook on gas dynamics or propulsion to demonstrate nozzle flows. Excellent learning assignments can be developed around this tool.
The "Export Data" feature is potentially very effective since users can export the output for a given case to a text file which can then be imported into Excel or similar programs for further analysis.
While it is certainly possible to use the applet merely as a "blackbox," hopefully students will still be required to go through the rigor of using the isentropic flow functions.
Ease of Use for Both Students and Faculty
The software is both easy and inviting to use. It can be used with minimal documentation, although a very good tutorial on flow through nozzles is an integral part of the learning object. The material is presented in terms familiar to engineering students taking courses in gas dynamics or propulsion.
All labels, buttons, and input boxes are fully functional and quite intuitive. Feedback to the user is very fast. Overall, the simulation applet is easy to use with minimal review of the introduction provided by the author.
When using Netscape 7.1, the JAVA Applet windows open as very small boxes on the screen, which the beginning user might not even notice. This could definitely be a source of frustration to the first-time user. Also, when using this browser, there is no apparent way to clear the input for one case so that another case can be run short of exiting the program completely and then re-entering. Entering the new values over the old values and hitting the "Compute" button has no effect. The old solution simply remains on the screen.
Also, the "Quit" button has no apparent effect. The program remains on the screen and the old values remain displayed. These problems are not observed with other learning objects that employ JAVA.
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