This online calculator computes the standard relations for compressible flow of a perfect gas, and is intended to provide a faster, more convenient alternative to printed tables and charts (e.g. NACA Report 1135). Three sets of relations, taken from standard aerodynamics texts, are included:
Isentropic Flow Relations Normal Shock Relations Oblique Shock relations
For each set of relations the calculator is used by selecting the variable to input, entering its value, and then pressing the calculate key. Output is immediately displayed. The calculator permits the value of the specific heats ratio to be entered as well. Also included is a scratchpad for intermediate calculations.
Type of Material:
A Java applet that provides an online calculator.
As a calculator for solving one-dimensional compressible flow problems. A fluid dynamics instructor may easily incorporate it into a lecture to demonstrate various compressible flow concepts and problem solution techniques. The calculator may likewise be used by students solving assigned homework problems in compressible fluid flow.
Identify Major Learning Goals:
To help students better understand the relationships that exist between pressure, temperature, Mach number, and flow area in compressible fluid flows.
Target Student Population:
Junior or senior undergraduate aerospace and mechanical engineering students.
Prerequisite Knowledge or Skills:
User needs to know the fundamentals of one-dimensional compressible flow including: Isentropic Flow Relations Normal Shock Relations Oblique Shock relations
Evaluation and Observation
The calculator is very useful for students solving problems in gas dynamics. It is certainly the online equivalent of the numerical tables presented in the classic NACA 1135 report. It includes all of the major parameters of interest in computing flows through nozzles and across shock waves, and provides the results in a rapid and accurate fashion. By allowing values of the specific heats ratio to be entered, the calculator becomes even more useful than the NACA 1135 tables, which used only the value of 1.40 appropriate for air. The rapid iterative calculation of the Mach number, given the A/A* ratio for nozzle flow, is a very useful element in the calculator since this is a difficult hand calculation.
Potential Effectiveness as a Teaching Tool
The calculator lends itself well to both classroom demonstration and homework assignments. It provides instantaneous calculations and permits the instructor or student to avoid the tedious process of referencing and interpolating charts and tables during a lecture or homework assignment.
Although not a major concern, if the website presented a discussion and the equations underlying the computations in the manner of the NACA 1135 report, this learning object would have even greater potential effectiveness as a teaching tool.
Ease of Use for Both Students and Faculty
The calculator is very easy to use, and the various input boxes are quite intuitive to anyone with a basic knowledge of gas dynamics. Its ease of use and immediate feedback allow students to focus more on the gas dynamics and less on the rather involved calculations. A nice feature is its use of scientific notation to represent very large and small numbers, something that many online applets fail to do.