After evaluating the response of user evaluation, it was found that dwfs-1.9 does not fulfill the requirements of the majority of interested organisations. A new potential flow solver, better suited to meet these requirements, is therefore implemented at the moment, using the experience gained in developing dwfs. In order to accelerate this development, support of dwfs-1.9 is limited to existing users.

To be notified when the new solver is available, send an email .


Considering the assumptions made in deriving the equations of potential flow, the physicist Richard Feynman concluded that the only fluid to comply with said assumptions must be... dry water. Well, then, this page is about the dry water flow solver, dwfs.


The boundary-elemnt formulation used in dwfs is the well-known Morino variant, although using linear source and doublet strength distributions on plane triangular element, which differs from the more common constant-strength surface elements. Triangular elements make surface mesh generation much easier, at least when sufficiently many elements can be used.

At the time of writing, the following types of simulation can be performed with dwfs:

  • Steady solutions in incompressible and subsonic compressible flow (i.e. no shocks).
  • Unsteady solutions in the Laplace or frequency domain, for incompressible or subsonic flow. Note however, that Laplace-domain computations for compressible cases are comparatively expensive due to the cost of integrating the oscillatory exponential kernel.
  • Time-domain unsteady simulations for incompressible flow, which can be useful to, e.g investigate the effect of concentrated nonlinearities on aeroelastic stability.
  • For meshes which contain control system definitions generated by sumo, control derivatives of all integrated loads are computed.
  • Mesh deformations are currently handled by assuming rigid-body motion about a fixed center of mass, superposed with structural deformation in modal subspace. Structural models can be retrieved from NASTRAN modal analysis files (.f06). Structural eigenmodes are automatically projected onto the aerodynamic surface mesh.
  • Extremely efficient integrated flutter solver based on a piecewise quadratic eigenvalue formulation.


In order to enable the use of automatically generated, large unstructured surface meshes, dwfs employs

  • Panel clustering, which reduces the computational and storage complexity from (at least) O(n2) to O(n log n). Although dwfs uses far less memory than a conventional panel method, it still requires about one Gigabyte for every 20 000 surface triangles.
  • Explicit multithreading for parallel execution of the most expensive steps on modern multicore processors. A speedup of 1.8 on two cores/processors and around 3.0 on four cores is typical.
  • Modern, object-oriented implementation in C++.

related publications

D. Eller: The flutter equation as a piecewise quadratic eigenvalue problem.
AIAA Journal of Aircraft 46(3), 1068-1070, May 2009.

D. Eller: Aeroelastic reduced order models.
Presented at SAAB Aerosystems Seminar, Kolmården, November 2008.

D. Eller: Friction, Freeplay and Flutter of Manually Controlled Aircraft. Presented at the International Forum for Aeroelasticity and Structural Dynamics, Stockholm, June 2007

D. Eller: An Efficient Method for Time-Domain Low-Speed Aerodynamics. TRITA/AVE 2005:40, Department of Aeronautical and Vehicle Engineering, KTH, December 2005

D. Eller and U. Ringertz. Aeroelastic Simulations of a Sailplane. TRITA/AVE 2005:41, Department of Aeronautical and Vehicle Engineering, KTH, December 2005

D. Eller. Efficient Flight Mechanics Simulation of Elastic Aircraft Configurations. Presented at the International Forum for Aeroelasticity and Structural Dynamics, Munich, June 2005

D. Eller and S. Heinze: An Approach to Induced Drag Reduction with Experimental Evaluation. AIAA Journal of Aircraft, 42(6):1478-1485, November 2005

D. Eller and M. Carlsson : An efficient aerodynamic boundary element method and its experimental validation, Aerospace Science and Technology 7(7):532-539, November 2003