Cobalt is a fast, reliable and robust unstructured flow solver. It's scalability has been demonstrated on tens of thousand of processors. Included is a wide range of boundary conditions, turbulence models and rigid body motion types.


Cobalt is a parallel, implicit, cell-centered, finite-volume, unstructured flow solver.  The spatial operator is a second-order accurate TVD scheme based on Godunov's original first-order accurate, exact Riemann method.  The temporal operator is a second-order accurate implicit method with Newton sub-iterations.

  • Equation Models:
    • Euler, Laminar and Turbulent
  • Gas Models:
    • Ideal Gas, Thermally Perfect Gas and Equilibrium Air
  • Flow Viz FIle Format


Cobalt has excellent parallel performance.  As you double your number of processors, your solution time is cut in half.  This will hold until the number of cells on each processors because relatively small.  As an example of scalability on 10,000 of processor, see the figure below.  This grid contained 49 million cells and as super-linear at 21,856 processors.scalability

Boundary Conditions

Cobalt offers a wide-range of boundary conditions.  There are nine boundary conditions types with several methods in each type.

List of Boundary Condition Types


  • Modified Riemann Invariants
  • Modified Riemann Invariants with Random Velocity Perturbations
  • Original Riemann
  • User Profile

Solid Wall

  • Adiabatic No-Slip
  • Isothermal No-Slip
  • General No-Slip
  • 1-D Heat Equation No-Slip
  • Slip
  • Symmetry
  • Axis-of-Symmetry 


  • Static Pressure
  • Total Pressure
  • Mass Flow
  • Corrected Mass Flow
  • Mach Number
  • Valve (allows the outflow area to vary with time)


  • Riemann Invariants
  • Total Pressure and Temperature
  • Mass Flow and Total Temperature
  • Burning Grain.Adiabatic No-Slip 


  • Disk
  • Wind Mill
  • User-Specified Wind Mill
  • Blade-Element 


  • Linear
  • Circumferential


  • Specified
  • Coded

Oscillating Inflow/Outflow

  • Mass Flow
  • Velocity

Turbulence Models

Cobalt includes 16 turbulence models from one-equation RANS to DES to four equation RANS/LES hybrids.

List of Available Turbulence Models

  • Spalart-Allmaras (SA), RANS, 1 equation
  • SA with Delayed Detached Eddy Simulation (DDES), hybrid RANS/LES, 1 equation
  • Menter Baseline (BSL), RANS, 2-equation
  • Menter Shear Stress Transport (SST), RANS, 2-equation
  • SST with DDES, hybrid RANS/LES, 2-equation
  • Wilcox (2006) k-ω, RANS, 2-equation
  • Cobalt Solutions modified Wilcox k-ω, RANS, 2 equation
  • SA with/ Rotation and Curvature Correction (SARC), RANS, 1 equation
  • SARC with DDES, hybrid RANS/LES, 1 equation
  • SST with Scale-Adaptive Simulation (SAS), hybrid RANS/LES, 2 equation
  • Hellsten Explicit Algebraic Reynolds Stress Model (EARSM), RANS, 2-equation
  • EARSM with Curvature Correction, RANS, 2 equation
  • SST with Gamma-Theta (GT) boundary layer transition model, RANS, 4-equation
  • SST-GT model with DDES, hybrid RANS/LES, 4-equation
  • SST-GT model withfreestream sustainment terms, hybrid RANS/LES, 4-equation
  • SST-GT model with DDES and freestream sustainment terms, hybrid RANS/LES, 4-equation


Multiple grids acting as a single grid system can be simulated using our Overset module.  For more information, see Overset Module.

Rigid Body Motion

Rigid-body motions in Cobalt belong to two broad classes: ‘free’ and ‘specified’.  Free motions are those where the motion is determined by the forces and moments acting upon the body. Specified motions are those where the user specifies the motion.   With the Overset module, grids can have independent motions.

List of RBM Types


  • Oscillation
  • General Rotation and Translation
  • Arbitrary 


  • 1 DoF
  • 6 DoF
  • Feedback Control (via Matlab interface)

System Requirements

Linux (RH 6.0 or later), OpenMPI (version 1.6.5 or 1.8.4) and gfortran