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CHAPSim



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CHAPSim

CHAPSim is a high-fidelity DNS solver for incompressible turbulent flow and heat transfer, developed within CCP-NTH for fundamental research and community capability.

Overview

CHAPSim is a high-fidelity Direct Numerical Simulation (DNS) solver for incompressible turbulent flow and heat transfer in canonical configurations such as channel and pipe flows.

The current actively developed version is CHAPSim2, which provides higher-order numerical accuracy and improved parallel performance for modern HPC systems.

CHAPSim1 is no longer actively supported, and users are encouraged to transition to CHAPSim2 for ongoing development and future capability.

History

CHAPSim has evolved from an academic research code into a modern, open-source community capability within CCP-NTH, with current development centred on CHAPSim2.

The original version of CHAPSim was developed by Dr Mehdi Seddighi during his PhD studies (from 2007), focusing on simulations of isothermal, incompressible, unsteady turbulent channel flows. The implementation was written in Fortran 77 and drew on numerical approaches presented in Paolo Orlandi’s Fluid Flow Phenomena: A Numerical Toolkit. The code was subsequently extended by Dr Wei Wang (2013–2015) to support thermo-fluid applications, with redevelopment in Morden Fortran Language and enhanced its numerical capability and instability.

Building on this foundation, CHAPSim2 has been developed as the primary CCP-NTH community code, providing higher-order spatial accuracy (up to sixth order) and multi-dimensional parallelisation for modern high-performance computing systems. The latest production release is v2.1.0 (30 January 2026).

An earlier version, CHAPSim1.0, was released in 2020 as part of the initial open-source effort, employing second-order spatial discretisation with one-dimensional parallelisation. This version is now retained for reference only and is no longer actively supported.

CHAPSim2 is released as open-source software under the BSD 3-Clause License, and its development is led within CCP-NTH with contributions from STFC Daresbury Laboratory, and the University of Sheffield.

Capability

  • High-order spatial accuracy (2nd to 6th order schemes)
  • Direct Numerical Simulation (DNS) for turbulence and heat transfer
  • MPI-based parallelisation with 3-D FFT-based solvers
  • Support for Cartesian and cylindrical geometries (channel and pipe-type flows)
  • Variable property flows and thermal coupling
  • GPU acceleration (validated on NVIDIA H100 systems)
  • Scalable to large HPC systems (i.e. Archer 2 for over 64k+ CPU cores) and billion-cell simulations

Access & Repository

CHAPSim2 (Active Version)

The official CHAPSim2 repository is maintained under CCP-NTH and hosted on GitHub.
git clone git@github.com:CCP-NTH/CHAPSim2.git

CHAPSim1 (Legacy)

CHAPSim1 is retained for reference purposes but is no longer supported or actively maintained.

Impact

CHAPSim has been used to generate high-fidelity datasets for turbulence and heat transfer research, supporting both fundamental studies and model development.

A list of publications using CHAPSim will be made available and regularly updated here.

Acknowledgement

Publications and outputs using CHAPSim should acknowledge support from CCP-NTH and CoSeC. A reference publication will be provided here in due course.

“This work made use of computational support by CoSeC, the Computational Science Centre for Research Communities, through CCP-NTH.”
Team member