This program is designed to be interactive, so you have to work with the program. There are several different types of widgets that you use to work with the program.
- There are a variety of choices that you must make regarding the analysis and the display of results by using a choice box. A choice box has a descriptive word displayed and an arrow at the right of the box. To make a choice, click on either the arrow or the current choice word, hold down, and drag to make your selection. The new selection is indicated by a change in the word. A recent security patch has changed the way that choice boxes operate. This can result in a condition where you can’t change from Imperial to Metric units. To overcome this problem, we have included an Override option on the choice boxes on the control panel. If you get stuck, click on Override then click on your choice; it will then work correctly.
- The current values of the design variables are presented to you in text boxes. By convention, a white box with black numbers is an input box and you can change the value of the number. A black box with yellow or red numbers is an output box and the value has been computed by the program. To change the value in an input box, select the box by moving the cursor into the box and clicking the mouse, then backspace over the old number, enter a new number, then hit the Enter key on your keyboard. You must hit Enter to send the new value to the program.
- For most input variables you can also use a slider located next to the input box. Click on the slider bar, hold down and drag the slider bar to change values, or you can click on the arrows at either end of the slider. If you experience difficulties when using the sliders to change variables, simply click away from the slider and then back to it. If the arrows on the end of the sliders disappear, click in the areas where the left and right arrow images should appear, and they should reappear.
- Some graphics decisions are selected by pushing buttons. To push a button, move the cursor over the button and click the mouse.
The program screen is divided into four main parts:
- On the top left side of the screen is a graphic of the engine you are designing or testing. In the Design Mode, the drawing is a schematic, while in Tunnel Test Mode the drawing is an animation.
- On the upper right side of the screen are choice buttons which control the analysis. You can select the type of analysis, the type of output to be displayed, and the units to be used in the calculations. You will always see the overall engine performance displayed as thrust, fuel flow, airflow, and computed engine weight.
- On the lower right side of the screen are the results of engine performance calculations. The output can be presented as numerical values of certain parameters, graphs of engine performance, or as photos of the engine parts with descriptions of their purpose. You select the type of output displayed by using the red choice button labeled “Output:” on the upper right panel.
- On the lower left side of the screen various input panels are displayed. You can select the input panel by clicking on the name or the component in the graphic at the upper left.
Please note: the simulation below is best viewed on a desktop computer. It may take a few minutes for the simulation to load.
Engine Design Process
You can choose from four different types of engines: a simple turbojet, a jet with afterburner, a turbofan engine, or a ramjet. Selections are made on the graphics window by clicking on the engine name. The chosen engine is shown in yellow. Depending on the engine type, different input panels appear at the lower left.
The design process begins by selecting the design Flight Conditions. The Flight input panel lets you change the Mach number, airspeed, altitude, pressure, temperature, and throttle and afterburner settings. There are several different combinations of these variables available for input using the choice button on the input panel. The pressure and temperature are computed as functions of the altitude by using a Standard Day atmospheric model.
Design variables for each engine component can also be varied. The components and variables include the Inlet (pressure recovery), Fan (pressure ratio, efficiency, and bypass ratio), Compressor (CPR, compressor efficiency), Burner (fuel, maximum temperature, efficiency, pressure ratio), Turbine (turbine efficiency) and Nozzle (maximum temperature, efficiency, A8/A2). As you choose a different component the part of the engine being affected is highlighted in the graphic by changing from its default color to yellow. If you change the Output Display to “Pictures” you can view an actual photograph and description of each engine part.
Engine Size can be specified by either the frontal area or the diameter. As the engine size changes, the grid background changes in proportion to the size. The distance between any two grid lines is 1 foot.
The program will calculate an average weight of the engine that you design. The thrust to weight ratio of the engine is displayed in the numerical output and is a measure of the efficiency of the engine. The weight depends on the type and design of the engine, the size of the engine, and the component materials. The program begins with standard materials for the components, but you can change the materials and see the effects on weight of the engine. Just push the blue Materials choice button on any component input panel. You can also select to define your own material by choosing My Material from the menu. Just type in your own values for material density and temperature limit.
The program will check the temperature throughout the engine design against the material limits. If you exceed a limit, a flashing warning will occur in the schematic. You can see the temperature limits by choosing “Graphs” in the Output display on the control panel. Then select Temperature as the type of graphics display. You can also find which component is exceeding the temperature limits by selecting “Component Performance” on the Output display and looking for the red temperature display. (For the afterburner and the ramjet, the graphical temperature limits are based on the flow temperature, not on the material temperature, and are slightly higher than the material limits. Cooling airflow is often used along the walls of these components to keep the material temperature within limits.)
Control Panel Choices: Mode, Units, Output Display
The program works in two modes: Design or Tunnel Test Mode. In the Design Mode, you can change design variables including the flight conditions, the engine size, the inlet performance, the turbo machinery compressor and turbine performance, the combustors or burner performance, or the nozzle performance. For a turbofan engine design you can also vary the fan performance and the bypass ratio. In Design Mode, any change in an input parameter produces a new engine design. You must be very careful when drawing conclusions about the effects of input variables on performance because you are not comparing the effects on the same engine; you are comparing one engine against another engine.
In Tunnel Test Mode, you are only working with one engine. You can vary only the flight conditions and you can not change any of the component design parameters except the throttle setting. The values of some of the performance parameters like inlet recovery and nozzle area may change according to choices that you made during design. In Tunnel Test Mode you are evaluating the off-design performance of the engine model which you specified in Design Mode. You can use any of the output panels to see how the various engine parameters change with speed, altitude, or throttle setting. You can also load models of real turbine engines for comparison with your design. You can always reload your design to continue testing. In Design Mode, you can use the existing engine models as good starting points for your design.
The calculations can be performed in either Metric or Imperial (English) units. You can always return to the default conditions by pushing the red Reset button at the upper right.
The red Output menu allows you to change the contents of the output window on the lower right side of the screen. You can choose to display output boxes with numerical values of the engine and component performance, as described below. Or you can display photographs and descriptions of each engine part. Or you can display graphs of the variation of the value of pressure and temperature at various stations through the engine. You can also display a T-s Plot or a P-v diagram , which are used by engineers to determine engine performance.
To generate your own performance plots, select “Generate” from the graphics window. The input panel will now display some additional buttons and sliders to generate a plot. Choose the variables to be plotted using the pulldown menus and then push the “Begin” data button. Set the value of the independent variable by using the slider or the type-in box. Push the blue “Take Data” button and a data point will appear on the graph. Set a new value for the variable and take another data point (up to 25 points in any order). When you are finished, push the “End” button and a line will be drawn through your data points. To start a new graph, push “Begin” and your old graph will vanish. When you are finished, push the red “Exit” button and you will return to free stream conditions.
Numerical Output from the program is displayed on two panels. The total engine performance is always displayed on the control panel panel at the upper right and includes the engine net thrust, the fuel flow rate, the engine air flow rate, the engine weight, the thrust to weight ratio, and the specific fuel consumption.
There are two additional performance panels that are displayed at the lower right. The Engine Performance output panel shows the fuel-to-air ratio, the engine pressure ratio (EPR) and engine temperature ratio (ETR), gross thrust, and ram drag. Additional component performance parameters, such as the nozzle pressure ratio (NPR), compressor pressure ratio (CPR) , engine thermal efficiency, nozzle exit velocity (V exit), free stream dynamic pressure (q0), and specific impulse (ISP) are displayed. Nozzle exit pressure (Pexit) and fan nozzle exit pressure (P fan exit) and the compressor face Mach number (M2) are also displayed. The Component Performance output panel shows the variation of total pressure and temperature at various stages through the engine.
Set the following conditions in EngineSim:
- Design Mode
- English Units
- Flight Conditions
The Airspeed should be 0, the Altitude 0, and the Throttle 100. Record the thrust
(F net) ___________and the Fuel Flow __________.
Now go ahead and change the altitude to 10,000 ft. and the Airspeed to 350. Did the thrust increase or decrease? Did the fuel flow increase or decrease? Thrust ________ Fuel Flow__.
What happens when you choose a different engine? Choose a jet with afterburner and record the thrust ___________ and the fuel flow ____________.
Choose a turbofan engine and record the thrust _____________ and the fuel flow________.
What can you conclude about the effect of an increase in altitude and airspeed on thrust? __________________________________ On fuel flow?__________________________
Which engine is most fuel efficient? _______________________________