HY-V SCRAMJET INLET Christina McLane Virginia Polytechnic Institute and State University

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1 HY-V SCRAMJET INLET Christina McLane Virginia Polytechnic Institute and State University Abstract Hy-V is an undergraduate student-led scramjet engine test project. There are multiple teams at several Virginia universities working in collaboration on the project. One of the Virginia Tech teams is designing the flow path for the scramjet engine. Three different inlets for this engine have been designed for future testing. These include a two-dimensional four-shock ramp inlet, a twodimensional three-shock conical inlet, and a three-dimensional streamline-traced inlet. Wind tunnel testing is scheduled and will examine the qualities of the flow in these inlets. The results of the tests will determine which inlet is chosen for the flight test of the scramjet engine. Introduction Before 960, ramjet engines were the main focus of high-speed flight research and development. Once the ramjet engine concept had been well explored, interest continued in extending its performance to hypersonic speeds. During the 960 s and 70 s, research of concepts for hypersonic airbreathing engines was pursued in the United States by WPAFB, Navy-China Lake & JHU/APL, and NASA. Many different scramjet projects have been seen over the years since the development of the concept of the scramjet, including the National AeroSpace Plane, NASA s Hyper-X program, and Australia s University of Queensland s HyShot program.,2 Related Work Hy-V is an undergraduate student-led scramjet engine test project. The goal is to design and build a scramjet research payload for launch from Wallops Island, VA in 2008 or Several Virginia universities are collaborating on this project, including Virginia Tech (VT), the University of Virginia (UVA), Hampton University, Old Dominion University, and the College of William and Mary. Currently, the mission is planned to launch using a Terrier Mk 70-Improved Orion rocket. The Terrier-Improved Orion rocket can carry a payload with a diameter of 4in. The mission is planned to have a suppressed ballistic trajectory in order to maximize the time that data collection is feasible. With a payload of 375lb, the maximum altitude is approximately 55,000ft with a data collection time of about 40s. VT and UVA, in particular, have experience in this field of study. VT has performed a previous sounding rocket mission, NRL MAGIC. This mission was launched using an Improved Orion rocket. VT has two different senior design teams working on this project. An Aerospace Engineering team is working on the flight systems and a Mechanical Engineering team is designing the scramjet flowpath. UVA has developed a scramjet combustor and the facilities to test it. Key features of this combustor include a constant area rectangular isolator and a rectangular combustion duct. An aeroramp injector and plasma torch igniter are included on one wall of the combustor. This wall later expands at a o 2.9 sweep. The cross section of the isolator is.0 x.5in and it extends 0in downstream. The combustor extends 4.6in downstream of the fuel injection site. A diagram of the UVA combustor can be found in Figure. McLane

2 Inlet Design There are many things to consider when designing an inlet, including the size of your inlet, the combustor being used, and the performance of the inlet. In this case, two of these three variables are fixed. The inlet must fit onto the Terrier-Improved Orion rocket, which can only carry a payload with a diameter of 4in. We have chosen to use UVA s combustor design, as it has already had significant research efforts made. Therefore, the inlet must be rectangular to fit the combustor. Performance is the most important consideration for an inlet, however. The inlet is where the most losses in the scramjet occur, and so it is most important to carefully design the inlet. Ideally drag is minimized while pressure recovery is maximized. In addition, the inlet must actually start. Starting occurs when the shock system is fully set up and the final reflection shock is swallowed, or sitting inside the inlet throat. Three different inlets have been developed. Bryan Barrett and James Hughet, of the Virginia Tech Mechanical Engineering senior design team, have both developed twodimensional inlets. In addition, Lance Jacobsen, president of GoHypersonic Incorporated, has developed a threedimensional streamline-traced inlet. The Barrett Inlet The Barrett inlet, illustrated in Figure 2, uses external compression to compress the incoming air. This inlet uses a series of angled ramps to create oblique shocks. The oblique shocks will increase the local pressure of the fluid but decrease the total pressure of the fluid. The objective of this inlet is to compress the air with the least losses in the pressure ratio. The placing of the compression ramps was done using Microsoft Excel and the oblique shock equations. The final result of this manipulation can be seen in Figure 8. The goal was to get all of the shocks to meet at one location for the reflection shock. The final reflection shock is based off the last oblique shock. The reflection shock determines the beginning of the inlet and the initial distance of the cowl from the beginning of the inlet. To allow for a certain range of error the distance of the inlet was increased and the cowl was extended. With the all of the shocks placed in the right area, the inlet ideally would start, but numerous articles on this subject beg to differ, as there are other problems to solve. One such topic was the area ratio. To help the inlet to start, the wind tunnel test model of the inlet was designed to increase its area up to and beyond the Kantrowitz Ratio. 3 Another consideration concerning starting was bleeding of the turbulent boundary layer. Calculating this boundary layer in itself is quite a task and can only be considered an estimate. To help control the issues that can occur because of boundary layer separation, the Barrett inlet will have a bleed slot behind the final shock, which can be seen in Figure 2. The scramjet test model is made up of the ramp, cowl, sun roof, and bottom base plate. The ramp contains the compression ramps, bleed slot, and pressure taps for wind tunnel measurements. The cowl is used to help contain the flow and creates the reflection shock. The cowl will also house the sun roof used to adjust the area ratio for the Kantrowitz ratio. The base plate is used to connect the inlet to the testing plate in the wind tunnel and to provide structure and support to the scramjet under the loads of the Mach 4 environment. The Hughet Inlet The Hughet inlet, illustrated in Figure 3, was designed to have the lowest drag coefficient while still having a geometry that McLane 2

3 will meet the restrictions made by the Terrier- Improved Orion rocket. With this concept in mind, an angular cone was used as the base of the design. The Hughet inlet uses a three shock system to slow the flow to meet the requirements for the combustor. The first and third shocks of this system are generated by the same turning angle. An illustration of this shock system can be seen in Figure 4. The first shock is generated by the initial turning angle of the cone, δ, and creates a shock angle of σ. The shock then reflects at the cowl. Since the shock wave angle will be greater then the angle of incidence, there is a new shock angle σ 2, which corresponds to the turning angle of δ 2. The wave is then reflected by the cone at a new σ 3, corresponding to δ 3, which equals δ. The Hughet inlet has a set design restriction of δ 3 = δ, so the relationship between the first and third shock must be generated with respect to δ 2. We must determine a turning angle δ 2 that will adequately slow the flow down, so that the third shock can then turn the flow to the required isolator speed. This can be done by forming a system of equations using the Law of Sines and the critical area ratio equation. The critical area ratio is given by A A 2 γ = + M M γ + 2 γ+ ( ) 2 2 γ As seen in this equation, the only independent variable is the Mach number. Since the isolator Mach number is known to be 2.5, if the angle of the first shock and the critical area are arbitrarily set, a relationship can be determined between the area after shock and the area after shock 3 which is also equal to sin( σ 2+ δ ) + + sin( σ 3 δ 2) sin(90 δ ) = A sin(90 ) sin( 2 2) sin( 3 2 δ σ δ σ δ ) This equation is generated by using the Law of Sines. With a relationship relating all the shocks together, the fluid characteristics can now be analyzed as a function of δ and δ 2 at a given free stream Mach number. Ideal and isentropic relationships are being used, which means that the generated relationship is not accurate; however, these relationships give a good idea of how the flow should behave. Due to the size and the complexity of the developed relationships a Matlab program was created to iterate through multiple options and output the required data. The starting characteristics here are dictated by the total pressure losses, including those due to shear at the walls. 4 Thus, due to the complexity of the analysis and the time frame restrictions, variable inlet geometry will be used to analyze any starting problems. The cowl door can open and close with limited freedom, as can be seen in Figure 5. Also, only half of the Hughet Inlet will be tested in the wind tunnel. The Jacobsen Inlet The Jacobsen inlet, illustrated in Figure 6 as it will be mounted in the wind tunnel, is a truncated streamline-traced Busemann inlet with several modifications made to the design for functionality, viscous corrections, and to mitigate starting issues. The inlet was designed by the selection of () () streamlines through an axisymmetric generic Busemann flowfield. 5 In addition to the inlet, a long constant-area duct was added downstream of the inlet throat allowing operability studies along with parametric bleed-hole starting experiments. The test model of the Jacobsen inlet can be seen in Figure 7. It is made by Stereo Lithography and will be plated with 0.00in of nickel. A (2) (2) McLane 3

4 Future Work All three inlets will be tested in the Virginia Tech 23 x 23cm supersonic/transonic wind tunnel. 6 Pressures will be measured at 7 to 50 different points along the inlet, depending on the design. Schlieren photographs will also be taken of each inlet during testing. 7 Based off the results of the testing, one inlet design will be chosen for the final research payload configuration. Conclusion Hy-V is a collaboration between several Virginia universities, with the goal of designing and flight testing a scramjet engine. One of the senior design teams from Virginia Tech is designing the flowpath for the scramjet payload. Three different types of inlets have been created for consideration. Wind tunnel testing will determine which inlet is chosen for the final flowpath design. The sounding rocket mission will be launched sometime between 2008 to Mumbai, India. Starting in Hypersonic Intakes, AIAA F. S. Billig, Pyrodyne, Inc., Glenwood, Maryland. L. S. Jacobsen, Air Force Research Laboratory, Wright-Patterson AFB, Ohio. Comparison of Planar and Axisymmetric Flowpaths for Hydrogen Fueled Space Access Vehicles, AIAA Virginia Tech Department of Aerospace and Ocean Engineering, Blacksburg, Virginia. Supersonic Wind Tunnel, son.php. 7 A. Davidhazy, Rochester Institute of Technology, Rochester, New York. Schlieren Photography Principles, References E. H. Andrews, SWALES Aerospace, Hampton, Virginia. Scramjet Development and Testing in the United States, AIAA E. T. Curran, Air Force Research Laboratory, Wright-Patterson AFB, Ohio. Scramjet Engines: the First Forty Years, AIAA D. M. Van Wie, F. T. Kwok, and R. F. Walsh, Johns Hopkins University, Laurel, Maryland. Starting Characteristics in Supersonic Inlets, AIAA P. Donde, A. G. Marathe, and K. Sudhakar, Indian Institute of Technology Bombay, McLane 4

5 Figure 4. An illustration of the shock system in the Hughet inlet. Figure. A diagram of the University of Virginia s scramjet combustor. Figure 5. The Hughet inlet wind tunnel test model. Figure 2. The Barrett inlet. Note the bleed hole at the top of the fourth ramp. Figure 6. The Jacobsen inlet as it will be mounted for wind tunnel testing. Figure 3. The Hughet inlet. Figure 7. The wind tunnel test model of the Jacobsen inlet before nickel plating. McLane 5

6 Inches Inches Figure 8. The compression ramps, cowl, and shock system for the Barrett inlet. McLane 6