Scramjet Propulsion
Description
Explore the cutting edge of HAP technologies with this comprehensive resource from an international leader in her field
Scramjet Propulsion: A Practical Introduction delivers a comprehensive treatment of hypersonic air breathing propulsion and its applications. The book covers the most up-to-date hypersonic technologies, like endothermic fuels, fuel injection and flameholding systems, high temperature materials, and TPS, and offers technological overviews of hypersonic flight platforms like the X-43A, X-51A, and HiFIRE. It is organized around easy-to-understand explanations of technical challenges and provides extensive references for the information contained within.
The highly accomplished author provides readers with a fulsome description of the theoretical underpinnings of hypersonic technologies, as well as critical design and technology issues affecting hypersonic air breathing propulsion technologies. The book's combination of introductory theory and advanced instruction about individual hypersonic engine components is ideal for students and practitioners in fields as diverse as hypersonic vehicle and propulsion development for missile defense technologies, launch aerospaceplanes, and civilian transports. Over 250 illustrations and tables round out the material. Readers will also learn from:
* A thorough introduction to hypersonic flight, hypersonic vehicle concepts, and a review of fundamental principles in hypersonic air breathing propulsion
* Explorations of the aerothermodynamics of scramjet engines and the design of scramjet components, as well as hypersonic air breathing propulsion combustors and fuels
* Analyses of dual-mode combustion phenomena, materials structures, and thermal management in hypersonic vehicles, and combined cycle propulsion
* An examination of CFD analysis, ground and flight testing, and simulation
Perfect for researchers and graduate students in aerospace engineering, Scramjet Propulsion: A Practical Introduction is also an indispensable addition to the libraries of engineers working on hypersonic vehicle development seeking a state-of-the-art resource in one of the most potentially disruptive areas of aerospace research today.
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Dora Musielak, PhD, is Research Professor in the Physics Department at the University of Texas in Arlington, Texas, United States. She is a NASA Fellow, an AIAA Associate Fellow, and has been invited to lecture at universities in China, France, Mexico, Panama, Italy, England, Spain, and the United States.
Content
Preface xiii
Acknowledgment xvii
1 Introduction to Hypersonic Air-Breathing Propulsion 1
1.1 Hypersonic Flow and Hypersonic Flight 3
1.2 Chemical Propulsion Systems 5
1.3 Classes of Hypersonic Vehicles 12
1.4 Scramjet Engine-Vehicle Integration 15
1.5 Chemical Propulsion Performance Comparison 17
1.6 Hypersonic Air-Breathing Propulsion Historical Overview 19
1.7 Scramjet Flight Demonstration Programs 23
1.8 New Hypersonic Air-Breathing Propulsion Programs 30
1.9 Hypersonic Air-Breathing Propulsion Critical Technologies 33
1.10 Critical Design Issues 36
Questions 37
References 38
2 Theoretical Background 41
2.1 Atmospheric Flight 41
2.2 Air Thermodynamic Models 50
2.3 Fundamental Equations 53
2.4 Thermodynamic Cycle of Air-Breathing Propulsion 56
2.5 Air-Breathing Propulsion Performance Measures 61
2.6 Shock Waves in Supersonic Flow 65
2.7 One-Dimensional Flow with Heat Addition 69
2.8 Closing Remarks 73
Questions 74
References 74
3 Aerothermodynamics of Vehicle-Integrated Scramjet 77
3.1 Aerothermodynamic Environment 78
3.2 Hypersonic Viscous Flow Phenomena 83
3.3 Laminar to Turbulent Transition in Hypersonic Flows 88
3.4 Hypersonic Flowfield for Propulsion-Integrated Vehicles 92
3.5 Convective Heat Transfer or Aerodynamic Heating 104
3.6 NASA X-43A Leading-Edge Flight Hardware 111
3.7 Inlet Blunt Leading-Edge Effects and Entropy Layer Swallowing 113
3.8 Inlet Shock-On-Lip Condition or Inlet Speeding 114
3.9 Shock-Boundary Layer Interactions in the Propulsion Flowpath 116
3.10 Inlet Unstart 118
3.11 Closing Remarks 119
Questions 120
References 120
4 Scramjet Inlet/Forebody and Isolator 123
4.1 Introduction 123
4.2 Engine Inlet Function and Design Requirements 123
4.3 Inlet Types 129
4.4 Inlet Compression System Performance 132
4.5 Hypersonic Inlet Designs 143
4.6 Inlet Operation: Start and Unstart 152
4.7 Inlet Aerodynamics 154
4.8 Isolator 157
Questions 161
References 161
5 Scramjet Combustor 165
5.1 Combustor Process Desired Properties 166
5.2 Combustor Entrance Conditions 167
5.3 Combustion Stoichiometry 172
5.4 Combustion Flowfield 174
5.5 Scramjet Combustor Geometry 192
5.6 Scramjet Combustor Design Issues 197
5.7 Closing Remarks 198
Questions 199
References 199
6 Fuels for Hypersonic Air-Breathing Propulsion 203
6.1 Introduction 204
6.2 Endothermic Fuels 208
6.3 Heat Sink Capacity of Hydrogen and Endothermic Fuels 210
6.4 Fuel Heat Sink Requirements 212
6.5 Ignition Characteristics of Fuels 214
6.6 Mixing Characteristics of Cracked Hydrocarbon Fuels 217
6.7 Structural and Heat Transfer Considerations 218
6.8 Fuel System Integration and Control 219
6.9 Combustion Technical Challenges with Hydrocarbon Fuels 219
6.10 Impact of Fuel Selection on Hypersonic Vehicle Design 221
6.11 Fuels Research for Hypersonic Air-Breathing Propulsion 223
Questions 224
References 225
7 Dual-Mode Combustion Scramjet 227
7.1 Introduction 227
7.2 Phenomenological Description of Dual-Mode Scramjet 229
7.3 Heat Addition to Flow in Constant Area Duct 230
7.4 Divergent Combustor and Heat Release 231
7.5 Combustor Mode Transition Studies 236
7.6 Closing Remarks 247
Questions 247
References 248
8 Scramjet Nozzle/Aftbody 251
8.1 Introduction 251
8.2 Nozzle Geometric Configurations 255
8.3 Nozzle Performance Parameters 260
8.4 Nozzle Flow Losses 265
8.5 SERN Design Approach 266
8.6 Nozzle Ground Testing Issues 268
8.7 Special Topics for Further Research 270
8.8 Closing Remarks 274
Questions 275
References 275
9 Materials, Structures, and Thermal Management 279
9.1 Hypersonic Flight Mission Characteristics 280
9.2 Aerodynamic Heating 281
9.3 Hypersonic Integrated Structures 285
9.4 High-Temperature Materials Requirements and Properties 295
9.5 Selected Materials for Hypersonics 296
9.6 Examples of Vehicle Development Structure and Materials 306
9.7 Materials and Structures Technical Challenges 312
Questions 315
References 315
10 Scramjets and Combined Cycle Propulsion 319
10.1 Aerospace Propulsion 320
10.2 Combined Cycle Propulsion Concepts 322
10.3 From Takeoff to Hypersonic Cruise 324
10.4 Ideal Cycle Analysis of Turbojet and Ramjet Engines 325
10.5 Single-Stage-To-Orbit and Two-State-To-Orbit Vehicles 342
10.6 Propulsion for Spaceplanes 343
10.7 Hydrogen for Hypersonic Air-Breathing Propulsion 352
10.8 Technical Challenges of Combined Cycle Propulsion 359
10.9 Closing Remarks 362
Questions 363
References 364
11 Ground Testing and Evaluation 367
11.1 Introduction 367
11.2 Airframe/Propulsion-Integrated Vehicle Design Requirements 367
11.3 Ground Testing Overview 369
11.4 Ground Testing for the NASA Hyper-X Program 376
11.5 Ground Testing for the USAF X-51A Waverider 390
11.6 ONERA Ground Testing for the European LAPCAT2 Combustor 392
11.7 Vitiated versus Clean Air Hypersonic Wind Tunnel 393
11.8 Diagnostics and Measurements for Scramjet Combustion 394
Questions 396
References 397
12 Analysis, Computational Modeling, and Simulation 401
12.1 Overview of Computational Fluid Dynamics and Turbulence 403
12.2 Surrogate-Based Analysis and Optimization (SBAO) 414
12.3 Flowfield in Highly Integrated Hypersonic Air-breathing Vehicle 416
12.4 NASA Hyper-X Program Computational Modeling Requirements 423
12.5 Overview of Selected CFD Analysis Cases 426
12.6 Closing Remarks 432
Questions 434
References 434
13 Hypersonic Air-Breathing Flight Testing 439
13.1 Introduction 439
13.2 Flight Operational Envelope 439
13.3 Flight Test Technique Concepts 440
13.4 X-43A: Air-lifted, Rocket-boosted Approach 444
13.5 Australia/USA Flight Experiments with Sounding Rockets 449
13.6 Russia CIAM and NASA Partnership for Scramjet Flight Testing 452
13.7 Hypersonic Flight Demonstration Program (HyFly) 453
13.8 Phoenix Air-Launched Small Missile (ALSM) 454
13.9 Gun-Launched Scramjet Missile Testing 455
13.10 X-43A Flight Test Mishap 455
13.11 Closing Remarks 457
References 458
Powering the Future of Transcontinental Flight and Access to Space 461
Glossary 469
Nomenclature 485
Index 489
1
Introduction to Hypersonic Air-Breathing Propulsion
We begin a study of hypersonic air-breathing propulsion systems, engines that take the oxidizer from the surrounding atmosphere and propel vehicles to sustained speeds greatly in excess of the local speed of sound, higher than Mach 5. Hypersonic flight with air-breathing propulsion is pursued for its potential to realize cost-effective access to space and high-speed cruise. Applications include civil transports, scramjet-powered missiles to fly in the Mach 6-8 range, both tactical and strategic, single-stage space planes, and multiple-stage-to-orbit vehicle configurations. Renewed interest in hypersonic sustained flight has increased research and development activities and made substantial advances in required technologies. The remarkable performance improvements promised by high-speed air-breathing propulsion were brought within our reach by the recent development of technologies related to scramjet engines and by their demonstration in flight. Figure 1.1 depicts an artistic view of NASA's X-43A aircraft that flew at Mach 7 and 10 to demonstrate the viability of hydrogen-fueled scramjet propulsion.
Hypersonic air-breathing propulsion is based on ramjets and scramjets, the simplest jet engines to propel a vehicle to hypersonic speeds within the atmosphere. These engines have no internal moving parts, as they do not require turbomachinery (mechanical compressor/turbine) to process the ingested ambient air.
The ramjet engine has three main components: an inlet, a combustion chamber, and a nozzle. The dynamic action of the freestream air is used to produce the compression in the inlet as the vehicle flies at high speed. This action is referred to as the ram effect. The higher the velocity of the incoming air, the greater the pressure rise. The fundamental principle underlying ram compression in the ramjet inlet lies in converting the kinetic energy of the air into pressure. The compressed air then enters the combustion zone where it is mixed with the fuel and burned. The hot, high-pressure gas flow then accelerates back to a supersonic exit speed through the nozzle to develop thrust.
The most distinctive feature of the ramjet is that combustion of fuel with air takes place after the flow has been slowed internally to subsonic speeds. Moreover, the air flow is compressed in several steps, including passing through one or more oblique shock waves generated by the forebody of the vehicle or of the diffuser, deceleration of the supersonic flow in a convergent duct, transforming the supersonic flow into subsonic flow through a normal shock wave system, and further decelerating the subsonic flow in a divergent duct. Ramjets are suitable for applications where the flight Mach number is in the range 3-5 and are used mainly for supersonic flight.
Figure 1.1 Artistic rendition of scramjet-powered hypersonic cruiser.
Source: NASA.
When the flight Mach number exceeds about 5, deceleration of the ingested airflow to subsonic conditions would cause it to reach unacceptable high temperatures. To extend the flight regime above Mach 5, the scramjet was conceived. In this type of ramjet, the hypersonic inlet airflow is diffused only to supersonic speed prior to mixing it with fuel in the combustor. Hence, the combustion process takes place at locally supersonic conditions. The engine operating in this mode becomes a scramjet, an acronym standing for "supersonic combustion ramjet," a name used to emphasize that the combustion of fuel and air must occur in a supersonic flowfield relative to the engine. Scramjets in fully supersonic combustion mode begin to produce thrust flying at speeds of at least Mach 4 and would operate as long as there is sufficient air to pass and process through its inlet; the theoretical maximum operational speed for scramjets is unknown, but it could effectively reach about Mach 12.
There is a wide range of speed and altitude over which air-breathing propulsion is capable of higher specific impulse (I sp ) than is rocket propulsion. The I sp parameter indicates how much thrust the engine produces per every unit mass of propellant (fuel plus oxidizer) it uses per second. Since the air-breathing engine does not need to carry oxidizer on board, its specific impulse is much higher than that of the rocket. Scramjets are therefore the most efficient air-breathing engines, that is, with the highest (fuel)-specific impulse, at flight Mach numbers above 5. To capitalize on such advantage, much effort has been devoted to developing hypersonic air-breathing propulsion (HAP) systems to achieve hypersonic flight within the Earth's atmosphere. One such HAP concept is the dual-mode scramjet (DMSJ), an engine that operates both as ramjet (subsonic combustion) and as scramjet (supersonic combustion) in order to propel a vehicle in a flight Mach number ranging from 3.5 to 12 (the upper limit in scramjet operational Mach number is still unknown). However, due to its minimum functional speed, scramjets require acceleration by other means in order to become operational for takeoff.
For some military applications, air-breathing hypersonic vehicles can be air or ground-launched attached to a rocket motor that will accelerate the craft to the take-off speed of the scramjet. Other applications require to integrate the scramjet engine with a low-speed propulsion system (e.g. turbojet, turbofan) in order to provide the capability of propel a vehicle from the runway all the way to its maximum hypersonic speed.
Powered by scramjet engines, hypersonic vehicles scoop the oxygen required for fuel combustion from the atmosphere, and this reduces tankage requirements and airframe mass. In fact, for missile propulsion, the ramjet is very competitive with the rocket because it is simple in construction and has greater range for the same propellant weight. These characteristics are particularly attractive for military applications where simplicity and low initial cost are essential features of devices that must function on demand and never return. Moreover, hypersonic vehicles propelled by air-breathing propulsion promise affordable and rapid access to space and hypersonic cruise. Scramjet propulsion flight demonstrator programs (e.g. X-43A, X-51A, HIFiRE) have already proven that HAP vehicles are technically feasible. However, more flights and flight-test programs are required to demonstrate sustained cruise and acceleration to establish the DMSJ engine as a viable and mature hypersonic air-breathing propulsion system.
Moving at hypersonic speeds, a vehicle will naturally generate a massive amount of heat that must be properly managed. The vehicle and its integrated propulsion system must be fabricated with advanced materials designed to withstand those high temperatures, materials with high strength, and high toughness. Hypersonic vehicles travel very fast, getting hot enough to melt most traditional metals, so engineers are developing new material formulations for hypersonic craft to survive such harsh environment.
This book intends to provide the technical background to describe the fundamental characteristics of high-speed air-breathing engines, focusing on the technologies that are being developed to advance the DMSJ to power future hypersonic flight.
1.1 Hypersonic Flow and Hypersonic Flight
For air-breathing propulsion, hypersonic flight is interpreted to mean flight speeds V 0 higher than five times the speed of sound, that is,
where M 0 denotes a vehicle's flight Mach number and a 0 is the local speed of sound.
For the analysis of hypersonic air-breathing propulsion, we can define hypersonic flow as the regime where the calorically perfect gas model for air becomes invalid. For calorically perfect gas or temperatures less than 400 K, the specific heats c p and c v are constant. As the air temperature increases, in the range of temperature 400 K < T < 1700 K air behaves as a thermally perfect gas, the value of the specific heats is function of temperature; and thus the specific heat ratio (? = c p /c v ) is also a function of temperature.
At temperatures above 1700 K (3000 °R), the equilibrium of specific heat (c p ) of air depends strongly upon both temperature and pressure because chemical reactions have become important. Hence, ? reaches a value of 1.286 when the formation of nitric oxide (NO) begins. When nitrogen is released during combustion, it combines with oxygen atoms to create NO, which then combines with oxygen to create nitrogen dioxide (NO2). At temperatures above 1700 K, chemical reaction and dissociation become very complicated and cannot be treated with a simple gas model.
We can also consider the value of the freestream total or stagnation temperature that would cause real gas effects to occur. Let us consider the total to static temperature ratio,
(1.1)where T t0 is the freestream total temperature, M 0 is the flight Mach number, and the subscript 0 denotes the undisturbed freestream flow conditions far ahead of the vehicle as seen from the reference frame of the vehicle. When we substitute a representative value...
