Scramjet

From Biohack

(Redirected from Scramjets)
Jump to: navigation, search

Scramjet stands for hypersonic combustion ramjet. Use the scramjet to get into orbit from the planet-surface or for propulsion in dense magnetic clouds. David Dalrymple mentioned to me the X-43 scramjet, which uses hydrogen reactions onboard as fuel, so as to react to the air-intake. The development of an easy-to-make scramjet is important for space-access. Once in space, we can develop a lox economy as suggested by John Wilke et al. The lox economy will be especially possible when we learn how to make lox in orbit.

Contents

[edit]

Launching a scramjet from the surface

  • How does a scramjet accelerate, if it starts at zero velocity? The air-intake is practically zero (unless there is wind, but relying on wind for launch is not a good idea).
  • Hybrid scramjet (see below) will allow takeoff from the surface. Using lox would be an interesting method especially with the lox-related machinery that John Wilke and friends are planning on releasing into space (of course, this version would be for DIY surface lox production).
[edit]

Building the metal frame of a scramjet

[edit]

Aerodynamic efficiency of a scramjet

  • Drag forces?
  • Heat flow over the surface of the hull?
[edit]

Software for CFD

  • Computational fluid dynamics
  • GASPv4
  • Navier-Stokes equations -> Euler equations -> full potential equations -> linearized potential equations
  • " The first paper on a practical three-dimensional method to solve the linearized potential equations was published by John Hess and A.M.O. Smith of Douglas Aircraft in 1966. This method discretized the surface of the geometry with panels, giving rise to this class of programs being called Panel Methods. Their method itself was simplified, in that it did not include lifting flows and hence was mainly applied to ship hulls and aircraft fuselages. The first lifting Panel Code (A230) was described in a paper written by Paul Rubbert and Gary Saaris of Boeing Aircraft in 1968. In time, more advanced three-dimensional Panel Codes were developed at Boeing (PANAIR, A502), Lockheed (Quadpan), Douglas (HESS), McDonnell Aircraft (MACAERO), NASA(PMARC) and Analytical Methods (WBAERO, USAERO and VSAERO). Some (PANAIR, HESS and MACAERO) were higher order codes, using higher order distributions of surface singularities, while others (Quadpan, PMARC, USAERO and VSAERO) used single singularities on each surface panel. The advantage of the lower order codes was that they ran much faster on the computers of the time. Today, VSAERO has grown to be a multi-order code and is the most widely used program of this class. This program has been used in the development of many submarines, surface ships, automobiles, helicopters , aircraft, and more recently wind turbines. Its sister code, USAERO is an unsteady panel method that has also been used for modeling such things as high speed trains and racing yachts. The NASA PMARC code from an early version of VSAERO and a derivative of PMARC, named CMARC, is also commercially available."
  • "Calculation of potential flow about arbitrary three-dimensional bodies" (John Hess, A. M. O Smith)
  • Panel Code (A230) - Rubbert, Saaris.
  • Other codes:
    • PANAIR
      • PANAIR (an abbreviation for "panel aerodynamics") is a state-of-the art computer program developed to predict inviscid subsonic and supersonic flows about an arbitrary configuration by means of a higher order panel method. Generally speaking, a panel method solves a linear partial differential equation numerically by approximating the configuration surface by a set of panels on which unknown "singularity strengths" are defined, imposing boundary conditions at a discrete set of points, and thereby generating a system of linear equations relating the unknown singularity strengths. These equations are solved for the singularity strengths which provide information on the properties of the flow. PANAIR differs from earlier panel methods by employing a "higher order" panel method; that is, the singularity strengths are not constant on each panel. This is necessitated by the more stringent requirements of supersonic problem. The potential for numerical error is greatly reduced in the PANAIR program by requiring the singularity strength to be continuous. It is also this "higher order" attribute which allows PANAIR to be used to analyze flow about arbitrary configurations. PANAIR can handle the simple configurations considered in the preliminary design phase and later serve as the "analytical wind tunnel" which can analyze the flow about the final detailed, complex configurations.
    • A502
    • Quadpan
    • HESS
    • MACAERO
    • PMARC
    • WBAERO
    • USAERO
    • VSAERO
    • CMARC
    • PROFIL
    • Xfoil
    • WIBCO (transonic small disturbance equations)
    • The first description of a means of using the Full Potential equations was published by Earll Murman and Julian Cole of Boeing in 1970.
    • Program H
      • Frances Bauer, Paul Garabedian and David Korn of the Courant Institute at New York University (NYU) wrote a series of two-dimensional Full Potential airfoil codes that were widely used.
      • Grumfoil (Bob Melnik and his group at Grumman Aerospace)
    • FLO22
      • Antony Jameson, originally at Grumman Aircraft and the Courant Institute of NYU, worked with David Caughey to develop the important three-dimensional Full Potential code FLO22 in 1975.
    • Boeing's Tranair (A633) code
  • FLO57
  • CART3D (NASA)
  • SPLITFLOW (Lockheed)
  • NASCART-GT (Georgia Tech)
  • Lockheed's TEAM program
  • IAI/Analytical Methods' MGAERO program
    • MGAERO is unique in being a structured cartesian mesh code, while most other such codes use structured body-fitted grids (with the exception of NASA's highly successful CART3D code, Lockheed's SPLITFLOW code and Georgia Tech's NASCART-GT).
  • AIRPLANE
    • Antony Jameson also developed the three-dimensional AIRPLANE code (1985) which made use of unstructured tetrahedral grids.
  • ISES Euler program
    • Mark Drela and Michael Giles, for airfoil design and analysis.
    • MSES program
      • MISES (Harold "Guppy" Youngren)
  • NASA Ames' ARC2D code
  • OVERFLOW
  • CFL3D
[edit]

Free CFD codes

This section lists codes that are in the public domain, and codes that are available under GPL, BSD or similar licenses.

[edit]

Solvers

[edit]

Grid generation

[edit]

Visualization

[edit]

Miscellaneous

[edit]

Euler equations

Once again I note that these are developments built from fundamental components, such as partial differential equations, which are generally portrayed as "hard" even though they're exactly like ordinary differential equations and instead with respect to a function instead of being with respect to a variable. Why are partial differentials required to solving these problems? It seems to all be due to drag forces. I remember there being a Feynman method of partial differentiation or something, or at least a way to simplify the explanation of partial differential equations.

[edit]

Some thoughts

You have cubes of particles approaching your vehicle. The vehicle is a 3D object built from smaller 3D parts (ultimately many infinitismal pyramids). As the vehicle moves into the cube-of-particles (the atmosphere) (imagine it was first in a vacuum, and the particles do not move past the 'barrier' between themselves and the vacuum), the vehicle naturally must displace the particles, and imagine it as if the particles are under the laws of diffusion and brownian motion (namely, they will flow to places of lesser concentration of sameness). Therefore, you can begin to imagine that, as the front tip of the 3D object begins to displace the block-of-particles, the particles brownianly diffuse over the surface of the first 3D pyramid (assuming that there is only one front-most 3D pyramid to the entire object). As this first pyramid breaks into the block-of-particles, the particles should diffuse over the surface of the block. The collision wit the surface of the 3D pyramid should be one that is basically a that of the standard "a particle hits a slope" problem setup of physics (where a particle of some mass and some velocity intersects an inclined plane and then you are asked to figure out how far up the plane the particle moves). The particle not only moves up some distance of the 3D pyramid's surface, but eventually pressure from its neighbors joining it should cause the particle to be "squeezed" out of that location and to diffuse to another nearby location -- which, you then determine the rate of the particles coming by all around that "squeezed particle" and you realize that there must be a rate of the particles moving increasingly by (because remember, this squeezed particle is presumably a one-dimensional problem, and then all of the particles are moving by next to it, because the overall 3D object is moving into the block-of-particles), so it's then "squeezed" off the front of the object, and then gets slammed into another part of the object (assuming that the overall 3D object has a horizontal length greater than one 3D pyramidal unit that we were originally dealing with), and this will, again, impart force against the motion of the overall 3D object, and this will continue. The motion of gas against a surface, however, is probably not the same as the particle-hits-the-inclined-slope setup *because* in the hits-the-inclined-slope setup, the force of gravity is what eventually slows down the particle, whereas in this scenario, the force of the 3D object against the particle is what slows it down, and a gas particle will not necessarily just "sit there" (since, if you know its location perfectly, it will not be a gas particle by definition .. it'd be a super-condensate, probably). A first step might be to assume that (1) the surface of the 3D object is 'sticky' (making for inelastic collisions) and (2) any time a particle "sticks" to it, this particle also becomes "sticky".


NASA's CDISC project apparently uses pressure and velocity of particles versus the curvature of the local surfaces of the object that is undergoing the testing, which seems to be basically the method that I was describing above. CDISC has been implemented in CFD3D, TLNS3D, FLOMG, and OVERFLOW.


  • (1) Newtonian fluids -- this is a particle simulation like the one that I have already described.
  • (2) Continuous fluids -- this is where you figure out the velocity field of the fluid or gas over the surface of your object, and then from this velocity field you can calculate drag forces or even streamlines (the paths that particles will take given the velocity field). The Navier-Stokes are a statement of the conservation of momentum in terms of fields of differentiable points, it seems.
    • Why do you think they call it aerodynamics? It's not aerostatics (#1). It's aerodynamics because it's dynamical, a 'meta' level on top of the particles. You have a flow field around the object, and this flow field consists of different points that express different vectors ... it's kind of like stumbling into a hall of doors, and the points are the doors, where the door then leads you to some other location (the door is the vector). And at each of these different points you get changing momentum, mass, density, all sorts of interesting properties.
    • Derivation of the Navier-Stokes. Understandable, but not understandable as to how to apply this information to the modeling of an aerodynamically efficient craft.
    • CFD-wiki
[edit]

Hydrogen design

  • Note that this is not a hydrogen fuel cell.
  • 2008-03-04: I would also like to point out that conventional scramjets have only been tested when dropped from 35,000 feet at some subsonic speed via B52 superfortress, then when it drops the scramjet engine kicks on and proceeds to go 15 miles in seven seconds. The problem with this is that you need to have a B52, or at least a rocket that can take your craft up to more than enough height for it to get acceleration due to gravity and get the requisite start speed. However, it should also be possible to include onboard fuel for another sort of rocket to take it up to subsonic speeds at high altitude and then go freefall or just flip on the scramjet. This extra requirement of not only hydrogen but also other fuels significantly complicates the design.
    • Secondary fuel and rockets required. Pulse jet? Hybrid scramjet.
      • Either way the aerodynamic simulations still need to be ran. (also, see CD-ADAPCO for some interesting software, like STAR-CD which NASA supposedly uses for hypersonic simulations).


Here is my design for the hybrid scramjet. Flight plan: climb to 20,000 feet, cut the engines, free fall until g increases your velocity to Mach 4 (nose-dive should be highly efficient, right?), then the scramjets should cut on at any moment. Just keep on waiting. Yeah ...

  • First engine
    • Pistonless engine (Steve Harrington, Flometrics)
    • LOX. Also see the LOX machines (see John Wilke emails).
  • Second engine.
    • Scramjet.
[edit]

Fixing the Navier-Stokes equations for > Mach 2 flight

  • Howard Brenner
    • The importance of molecular diffusion of volume
    • On the Historical Misconception of Fluid Velocity as Mass Motion, Rather than Volume Motion
      • CFD simulators tend to generate a fluid field or velocity field. So people tend to view this as mass motion apparently, when it is really more like volume motion.
      • convection - the movement of currents within fluids; In fluids, convective heat and mass transfer take place through both diffusion – the random Brownian motion of individual particles in the fluid – and by advection, in which matter or heat is transported by the larger-scale motion of currents in the fluid. In the context of heat and mass transfer, the term "convection" is used to refer to the sum of advective and diffusive transfer.
      • Volume can diffuse without a simultaneous movement/diffusion of mass.
      • Euler made a mass-based definition of the velocity field in fluid continua.
      • Volume can diffuse on its own. (Note: would it be at all interesting to see a supercold fluid spontaneously find its way out of a bucket, and then use a radioactive tracer to figure out if the tracer itself moves back and forth during the seeping? This would mean that the volume is remaining relatively constant while the mass itself isn't necessarily the carrier of the volume.)
      • Thermophoresis, also called thermodiffusion or Soret effect[1], is the effect of a temperature gradient on particles, causing them to move from a hot plate to the cold. This effect is relevant to planetary differentiation and is exploited in the manufacturing of optical fiber and Uranium enrichment.
      • Mass velocity is not the velocity of the fluid continuum.
      • Bird, Stewart and Lightfoot -- chemical engineering textbook (40 year lapse in the two editions, both authored by the same men, an interesting feat indeed)
      • Newton and Euler began fluid mechanics with mass-points at momentum and thus the velocity variables are all about the centers of mass.
      • (Optically "tracking" the statistically-averaged movement of, say, a small group of photochromically-labeled or otherwise tagged molecules of the fluid does not qualify as being isomorphic with a tracer velocity measurement. Explicitly, a collection of molecules is not equipollent with a material tracer, the latter being be a single, rigid, corporeal entity.)
      • The mass-based velocity (v_m) is not equivalent to the tracer velocity in a fluid (v_t).
      • Density gradients in fluids
        • composition mass transfer gradients
        • temperature heat transfer gradients
      • In the absence of mass motion (v_m = 0), fluid is still in motion (v_t != 0).
        • The answer to the paradox lies in the fact while there is no mass motion of the fluid, there nevertheless exists a volumetric fluid motion driven by the fluid's thermal expansivity β acting in concert with the mass density gradient (engendered by the temperature gradient). This fluid motion is nonconvective and purely diffusive in nature.
      • There is a psychological predisposition to getting all of this wrong. Volume is a purely abstract concept like energy, entropy and momentum, and for some reason we have a tendency to think we can directly visualize volume.
      • In this context of the preceding remarks, it is informative to recite an anecdotal story related by the late, pioneering rheologist, Karl Weissenberg (1893- 1976) to a continuum-mechanical audience assembled at Carnegie-Mellon University in the early 1970's, which lecture I had the good fortune to attend. Prefacing his remarks (on Osborne Reynolds theory of dilatation in sand-water mixtures, during which he demonstrated a wonderfully simple illustrative experiment), Weissenberg noted that just prior to World War I he had served as a young applied mathematician at the Kaiser Wilhelm Institute of Physics in Germany, which Einstein visited periodically as part of the his "administrative" responsibilities as Director. On one of these visits, Weissenberg collared Einstein, telling him how much he admired his work, and seeking the latter's advice and counsel regarding an appropriate course of self-study that would permit his metamorphosis from applied mathematician to theoretical physicist. Without a moment's hesitation, Einstein suggested that his questioner learn how to design scientific instruments. Not understanding this response, Weissenberg posited that perhaps Einstein had misunderstood his original query, since his wish was to become a theoretical physicist, not an experimental one. Einstein assured him that he had not misunderstood the original question, and went on to elaborate that the only mechanism by which one could truly and deeply understand the fundamental meaning of a physical entity appearing in the guise of a mathematical symbol in a theoretical equation was by going through the mental exercise of systematically and methodically identifying the sequence of steps prerequisite to an unambiguous experimental determination of that entity. (Presumably underlying Einstein's response was the decisive role played in his 1905 special theory of relativity by his gedanken experiment involving the measurement of time, as well as by his then current efforts to understand the theoretical implications of the seemingly empirical equality of inertial and gravitational mass, an unequivocal experimental fact established earlier by Eötvös30 in 1889.)
      • 1. Brenner, H. "Fluid mechanics revisited." (Originally submitted in November 2002 to Phys. Rev. E under the title: "Inequality of Eulerian and Lagrangian velocities in molecularly inhomogeneous fluids".)
      • So basically the modified equations for Navier-Stokes equations are going to be based on the addition of a diffusive term for mass conservation to the mass-continuity equation, (and apparently modifications to the other equations as well. See my notes on the differences in the fundamental equations proposed).
        • The equations look of the same structure as the original equations, therefore their implementation in CFD simulators should be just as easy. The only difference is in figuring out what all of the variables mean.
  • Reese
[edit]

Metalworking

[edit]

Testing

[edit]

Wind tunnels

  • Amateurs have successfully designed these before. Do a linkdump.
[edit]

Hypersonic wind tunnels

  • Good luck?
[edit]

Engine-nozzle airframe coupling

See the study from the Langley Research Center by William J. Small, John P. Weidner, and P. J. Johnston. The forebody of the scramjet acts as an "inlet compression ramp", and the afterbody is an exhaust-nozzle surface.

  • Forebody inlet precompression (as opposed to free-stream inlet)
  • Exhaust-gas expansion
  • Large exhaust surface provides lift advantages.
  • axisymmetric engines/nozzles -- but another studied has found that integration of engine+airframe is better.
  • Trim drag penalties are possible with insufficiently optimized nozzles
  • Fixed-geometry scramjet
    • Rectangular modular scramjet engine that would be placed directly under the surface of the vehicle.
      • Swept compression surfaces
        • Localized pressure relief along the top surface of the engine to enable the scramjet to ingest the vehicle forebody boundary layer (thus eliminating the need for boundary-layer diversion or bleed).
      • Fuel-injector struts (need inlet starting at low-speeds ...)
      • In-stream fuel injection
        • Minimize the combustor length.
        • Minimize heat flux to the internal surfaces.
  • Supersonic combustion above mach 5 with this engine design. What's the difference between subsonic combustion and supersonic combustion?
  • Forebody shock layer
  • Increased Mach number generally requires an increasing engine size as a result of the reduced air density and specific impulse. At the same time increased Mach number decreases the depth of the forebody lower surface shock layer such that the inlet must be located at a more rearward body station where sufficient airflow is available. You have to minimize flow angularity and maximize available mass flow available for processing at the inlet face of the scramjet engine. A good forebody design allows a maximum utilization of the available area within the body shock layer. Forebody design/analysis - ref 10.
  • Tangent-cone methods
  • Compression surface forces on wings, tails, control surfaces --- see tangent-wedge methods of calculations.
  • Prandtl-Meyer expansion from free stream
  • Turbulent skin friction --> Spalding and Chi method.
  • Spillage forces
  • Pitching moments
[edit]

Splitting the design tasks of the scramjet

  • Engine design
    • Develop a framework of calculations for the engine such that nozzles and inlets can be appropriately adjusted for a certain design simultaneously.
  • Structural design of the overall craft
    • Are different structures optimized for moving through mostly homogenous liquids at different speeds? For example, for the craft that is optimized to fly at Mach 7, will it be optimized for flight at Mach 2?
Retrieved from "http://heybryan.org/mediawiki/index.php/Scramjet"
Personal tools