Three-dimensional Computer Code Research Articles

Distorted Flow Field in Compressor Inlet Channels

Solving the complex inlet-distortion related problems in turbojets or turbofans has become crucial to the successful development of new-generation engines. In order to curtail costs, reliable prediction methods, both analytical and numerical, must be developed and implemented. ONERA has been studying this problem for several years now. This paper reports on the preliminary numerical investigations of the three-dimensional flow field in the annular duct extending in front of a compressor with distorted inflow. The computational approach is a fully unsteady time-splitting, finite difference method solving the inviscid flow equations with nonuniform steady boundary conditions. Some analytical examples are presented and discussed. Matching of this three-dimensional computer code with models representing rotating or fixed blade rows is under way and will be reported on in a future contribution.

Assessment of Three-Dimensional Inviscid Codes and Loss Calculations for Turbine Aerodynamic Computations

An assessment of several three-dimensional inviscid turbine aerodynamic computer codes and loss models used at the NASA Lewis Research Center is presented. Five flow situations are examined, for which both experimental data and computational results are available. The five flows form a basis for the evalution of the computational procedures. It was concluded that stator flows may be calculated with a high degree of accuracy, whereas rotor flow fields are less accurately determined. Exploitation of contouring, leaning, bowing, and sweeping will require a three-dimensional viscous analysis technique.

Investigation of a dual inlet side dump combustor using liquid fuel injection

The characteristics of a dual-inlet side-dump combustor configuration suitable for ducted rocket missiles was investigated by injecting a liquid fuel (JP-4) into the two rectangular inlet ducts upstream of the dump plane. Cold flow water tunnel simulations were obtained by injecting small air bubbles into the inlet arms of a plexiglas model and illuminating these by a high intensity slit light source. Combustor performance was obtained by testing a similar stainless steel model on a combustor thrust rig. Combustion efficiency, combustor total pressure loss, lean blow-out limits, combustor pressure oscillations, and surface heating patterns were obtained. A threedimensional computer code using the k-e turbulence model was used to predict the corresponding cold flowfields with good agreement.

KOBRA3 - Three Dimensional Raytracing including Space-Charge Effects

Using the three-dimensional computer code KOBRA3, we have simulated the behaviour of the space charge compensating electrons within the potential of ion beams and magnetic fields. Measured field maps of a solenoid and a quadrupole have been used for these simulations. The predictions of the code are compared with measurements.

Estimating horizontal drain design by the finite-element and finite-difference methods

The presence of water is one of the most critical factors contributing to the instability of tailings embankments. Nonexistent or inefficient drainage facilities usually result in a high phreatic surface that can cause the embankment to fail. One possible solution, especially for remedial situations, is the installation of horizontal drains. An investigation into the effects of horizontal drains on the phreatic surface of tailings embankments was conducted by the Bureau of Mines. A laboratory model was constructed to correlate the effects of various drain spacing and length combinations with results from computer codes. A three-dimensional finite-element computer code and a two-dimensional finite-difference computer code were used. Two existing tailings embankments were modeled and potentiometric data were compared to the computer results. The two-dimensional finite-difference code and the three-dimensional finite-element code produced nearly the same location for the phreatic surface between drains. The location of the phreatic surface from the codes was slightly above the phreatic surface of one field application and followed the trend of the other closely. The phreatic surface location of the laboratory model was slightly above that of the computer-generated phreatic surface. The distance between the phreatic surfaces of these models became larger as drain length increased or drain spacing decreased. Dimensionless graphs were constructed for estimating phreatic surface location for embankments with horizontal drains.

Optimization on the end-shaping of a quadrupole magnet

In order to achieve the widest possible aperture of accelarator magnets, end-shaping is a well known method. To do this one has to deal with the three-dimensional fringe field inherent to each geometry. This may be done experimentally by a cut-and-try method or theoretically by a three-dimensional computer code. In any case, considerable time has to be consumed if one wants to get a conclusion which is a general as possible and which is useful in designing magnets. Fringe field optimazation on the end-shaping of the conventional quadrupole magnet was done by a cut-and-try method, where a very simple geometry of the end pole was chosen to get a general conclusion. The “cut-out ratio diagram” given as a conclusion is useful to designers of the conventional quadrupole magnet.

Finite β stellarators

A fully three-dimensional computer code based on an ideal magnetohydrodynamic model has been used to find stellarator configurations with finite critical values of the plasma parameter β. It is established that the WISTOR-U torsatron designed at the University of Wisconsin and the Heliotron E experiment constructed at Kyoto University have average β limits near 5 percent.

3D nonlinear calculations of resistive tearing modes

Recent numerical calculations of the evolution of resistive tearing modes have been central to the understanding of MHD activity and disruptions in tokamaks. The nonlinear three-dimensional initial value computer code RSF has provided many of these results. RSF assumes cylindrical geometry with a Fourier series representation in the two periodic coordinates and a finite difference representation in the radial direction. This choice makes RSF considerably more accurate and efficient than previous codes.

Effects of toroidal coupling on the stability of tearing modes

The time evolution of tearing modes in toroidal geometry is studied in the low-β and large aspect ratio limit. An initial value three-dimensional computer code which numerically advances the reduced set of resistive magnetohydrodynamic equations is employed. Toroidicity has, in general, a destabilizing effect on tearing modes in this limit. A generalization of Δ′ formalism can be used to study the linear regime. The results obtained in this way are in very good agreement with the results from the initial value code. The nonlinear phase of the evolution is also followed numerically. In the case of strong interaction of different helicities, a larger region of stochastic magnetic field lines results than in the cylindrical geometry case.

Numerical studies of new stellarator concepts

A three-dimensional computer code has been developed to study the magnetohydrodynamic equilibrium and stability of a diffuse or sharp boundary plasma in toroidal geometry. It is shown how equilibria with net toroidal current identically zero can be determined and how growth rates of instabilities can be calculated. Applications are made to an l = 2, 3 stellarator configuration that offers the possibility of achieving a critical value as high as 10% for the plasma parameter β.

Fragmentation of rotating protostellar clouds

With a three-dimensional hydrodynamic computer code, the behavior of rotating, isothermal gas clouds as they collapse from Jeans unstable configurations is examined in order to determine whether they are susceptible to fragmentation during the initial dynamic collapse phase of evolution. It is found that a gas cloud will not fragment unless (1) it begins collapsing from a radius much smaller than the Jeans radius (i.e., the cloud initially encloses many Jeans masses) and (2) irregularities in the cloud's initial structure (specifically, density inhomogeneities) enclose more than one Jeans mass of material. Instead of fragmenting, most of the models collapse to a ring configuration. The rings appear to be less susceptible to fragmentation from arbitrary perturbations in their structure than has previously been indicated in other work. Because the models, which include the effects of gas pressure, do not readily fragment during a phase of dynamic collapse, it is suggested that gas clouds in the galactic disk undergo fragmentation only during quasi-equilibrium phases of their evolution.

Fragmentation in a rotating protostar - A comparison of two three-dimensional computer codes

The collapse of an isothermal protostellar cloud with pressure, gravity, and rotation included is followed with two independent computer codes. For the initial condition, a nonaxisymmetric perturbation of mode m = 2 and 50% amplitude is introduced into a cloud of 1 solar mass with a mean density of 1.44 x 10 to the -17g/cu cm and a uniform angular velocity of 1.6 x 10 to the -12 rad/sec. The collapse is followed through an increase in density of over four orders of magnitude to the point where a binary protostar forms. The agreement between the results of the two calculations is good.

Applications of bumines three-dimensional finite element computer code to large mine structural problems : Karwoski, W J; Van Dillen, D E Proc 19th US Symposium on Rock Mechanics, Stateline, Nevada, 1–3 May 1978, V2, P114–120. Publ Reno: University of Nevada, 1978

Applications of bumines three-dimensional finite element computer code to large mine structural problems : Karwoski, W J; Van Dillen, D E Proc 19th US Symposium on Rock Mechanics, Stateline, Nevada, 1–3 May 1978, V2, P114–120. Publ Reno: University of Nevada, 1978

A three-dimensional finite-element computer code for the analysis of complex structures

General computational procedures are described with emphasis on FORTRAN based ‘dynamic’ storage allocation and adaptability of specialized input routines for the analysis of complex structures, including pump casings and pipe tees and elbows. A brief discussion is given on the algorithms used in this code for the formation and solution of banded linear equatons. The basic finite element building blocks, including isoparametric tetrahedra, pentahedra, and hexahedra are described. The results of a complex structural analysis, along with sample computer output, is presented.