Integrated Rocket Ramjet (IRR): Team Rocket

The goal is to design and model an Integrated Rocket Ramjet (IRR) engine design that will transition from the solid rocket phase to the liquid ramjet phase after reaching the designed speed while utilizing minimal breakaway parts or by means of control surfaces. The control surfaces will also serve as an inlet optimization tool to minimize exergetic losses into the combustion chamber and simultaneously maximize exit conditions for optimal thrust.

Background
This design project requires an understanding of compressible flow (also known as gas dynamics), thermodynamics of fluids including exergy analysis, and current propulsion system designs including ramjets. Below are some of the basic equations that are pertinent to this project scope.

Speed of Sound:


 * $$ a=\sqrt{\gamma R T_{abs}} \qquad \mbox{(1)} $$

where a = Speed of Sound, $$\gamma$$ = Specific Heat Ratio, R = Ideal Gas Constant, and $$T_{abs}$$ = Absolute Temperature.

Mach Number:


 * $$ M=V/a \qquad \mbox{(2)} $$

where M = Mach Number and V = Velocity.

Below is the equation of thrust for an air breathing engine.


 * $$ F_{thrust}=(\dot{m}+\dot{m}_{fuel})V_{out}-\dot{m}V_{in} \qquad \mbox{(3)} $$

where $$F_{thrust}$$ = Thrust, $$\dot{m}$$ = Mass Flow Rate, and V = Velocity.

The thermal efficiency of an aircraft engine.


 * $$ \eta_{th}=\frac{(\dot{m}+\dot{m}_{fuel})V_{out}^2-\dot{m}V_{in}^2}{2\dot{m}_{fuel}HC} \qquad \mbox{(4)} $$

where $$\eta_{th}$$ = Thermal Efficiency, and HC = Heat of Combustion.

The propulsive efficiency of an aircraft engine.


 * $$ \eta_{p}=\frac{2V_{in}F_{thrust}}{(\dot{m}+\dot{m}_{fuel})V_{out}^2-\dot{m}V_{in}^2} \qquad \mbox{(5)} $$

where $$\eta_{p}$$ = Propulsive Efficiency.

Together, the thermal and propulsive efficiency define the overall efficiency of an aircraft engine.


 * $$ \eta_{o}=\eta_{th}\cdot\eta_{p} \qquad \mbox{(6)} $$

where $$\eta_{o}$$ = Overall Efficiency.

CFD Remarks
Due to the difficulty of CFD supersonic internal flow simulations, it was determined that the water table would serve as a means to provide a qualitative analysis of transient supersonic internal flow characteristics. With CFD simulations, developing the mesh for internal flow is time consuming and difficult. Supersonic internal flow conditions are also challenging due to the conflict in setting proper boundary conditions for the inlet(s) and outlet(s). The Water Table will be used in later project development to generate 2D models to simulate flow through the IRR. The information gathered from Water Table simulations can be used to better develop meshes for CFD.

CFD and Water Table do not have a 1-to-1 relationship between the Froude (Fr) and Mach numbers for oblique shock wave simulations which means that further testing may likely require the formation of a dimensionless relation(s).

Water Table Remarks
It may be worth redesigning and/or rebuilding the Water Table to account for several shortfalls that occurred. Some ideas for improvement are :
 * Rebuild the water way so that it doesn't bow at the center. During testing, the Plexiglas would deflect at the center-line. To counter this, our team built an angled platform to reduce the depth of the laminar flow in the water way while also increasing the water velocity. This works, but the water way still bows. Perhaps a wider and longer water way can be developed to improve the water way structure, allow for variable water way angles, and increase the area of the water way surface to reduce wall interactions.
 * Construct something that can go in the reservoir tank that will laminarize the flow before it enters the water way. In conventional wind tunnels, this is done with honeycomb mesh. It was proposed that the same effect could be obtained by using bundles of straws and placing them into the reservoir before entering the water way.
 * Rebuild the reservoir with sturdier materials. One day, our team was showing off the Water Table to Dr. Crepeau and Dr. Xing because it was operational. The reservoir tank seam along the back (opposite of the water way) began to leak. Suddenly, it burst open splashing several gallons of water on our advisor Dr. Tao Xing. To fix this, all seams were chemically welded using an acid compound. It worked, but there is no guarantee for how long it will last.
 * Implement vibration absorbing material to reduce or eliminate interference with the water way. During simulation, it can be observed that the water vibrates. This has been reduced by implementing foam upholstery material underneath and around the 1/2 hp pump in the receiving tank, but it is possible to reduce it further or even eliminate it entirely.
 * Use bottom side lighting to better show the hydraulic jumps in the water way. It is sometimes difficult to see the ripples when there is topside lighting.

Future Team(s)
It was identified early on that a fundamental understanding of compressible flow is needed to comprehend the flow characteristics of the inlet. With the water table, now an analogy can be used to develop that understanding using concepts learned in fluid dynamics. But future teams would likely need gas dynamics to be able to fully contribute.

CFD prior to this design challenge would have been substantially better for the development of the project. It is a hard program and skill to learn, but it has provided substantial results that can be quantified using gas dynamics.

Document Archive
[[Media: TeamRocket_Water_Table_Instructions_2015.pdf|Water Table Instructions]]

[[Media: TeamRocket_Water_Table_Drawings_2015.pdf|Water Table Drawings]]

[[Media: TeamRocket_CFD-WT_Analysis_2015.pdf|CFD vs. Water Table Analysis]]

[[Media: EXPO_2015_Poster_IRR_V.1.2.pdf|EXPO 2015 Poster]]

Research Literature
Johns Hopkins - Integrated Rocket Ramjet History

SJSU Munoz, A. - Combined Cycle Engines

Unified Rocket Ramjet Engine I

Unified Rocket Ramjet Engine II

Georgia Tech - Optimizing Diffuser for Pressure Recovery

CalPoly Stone, P.C. - Ramjet Combustion Chamber

CalPoly Humphrey, C.C. - Ramjet Design and Fabrication

CalPoly Selin, K. - Ramjet Fuel System

UNLV Nelson, S.E. - CFD vs. Water Table Experiments

Other Resources
AeroMech Compressible Flow for Students

NPTEL E-Learning Courses