Advanced science.  Applied technology.


Numerical Propulsion System Simulation (NPSS)

Numerical Propulsion System Simulation (NPSS) is an object-oriented, multi-physics, engineering design and simulation environment that enables development, collaboration and seamless integration of system models.

image of flow engine cycle flow chart Generic engine cycle model for analysis in NPSS including inlet, compressor, burner, turbine, duct and nozzle

Model definition is performed through input files. A new integrated development environment (IDE) is under development to facilitate NPSS work for new and casual users. NPSS contains NIST-compliant gas property packages for a variety of applications. The tool is based on object-oriented programming to facilitate user-definable elements and functions. NPSS also includes a sophisticated solver with auto-setup, constraints and discontinuity handling. Typical solution modes include preliminary design, off-design performance, transient performance and flight data correlation.


IDE for NPSS currently in development IDE for NPSS currently in development

Primary application areas for NPSS include aerospace systems (i.e. engine performance models for aircraft propulsion), thermodynamic system analysis such as Rankine and Brayton cycles and various rocket propulsion cycles, and industry standardization for model sharing and integration.

NPSS Development Projects

The NPSS consortium manages three development project areas in support of the NPSS user community, NPSS core, NPSS IDE and NPSS EMI. These project areas are organized to support key development themes established by the Governing Board of the NPSS Consortium.


The NPSS core project is focused solely on updates, fixes and additions to the capabilities of the NPSS environment. This includes the various functions of the NPSS interactive environment, the various converters for developing compiled content, the included functions that support model development and operation, and the numerical routines used by the solver for steady state and transient solutions.

The NPSS development team has been adding new capabilities and addressing user-identified corrections since the release of NPSS v2.6.1 in December of 2013. The ability to specify a unit system is a significant new feature introduced in NPSS v2.7. Other updates include support for 64-bit runtimes under Windows® and Linux® and enhanced file dependency and object hierarchy tracking. A number of user-identified changes have been implemented to improve documentation, reduce memory footprint, increase execution speed, enhance core functionality, and address user-specific requirements. One such change is the removal of the switchDes option variable from the assembly class. This change supports DLM generation with user defined assemblies. If required, a switchDes variable may be declared as an option variable by the user for compatibility with existing models.

The Executive Summary provides a more detailed explanation of the various improvements included in this release as well as some insight into upcoming improvements planned for release late in 2015. Improvement areas highlighted include updates to the APIs, the solver, the thermo packages, various utilities, units, and the associated documentation.


As mentioned above, the IDE is a new interface under development by the NPSS consortium with the goal of making NPSS more accessible to the new and casual user. Advanced users expect to find the new tool helpful as well, especially for new model development and the study of unfamiliar existing models. The IDE development is taking advantage of all the capabilities within NPSS, and allows for reading of existing NPSS models in a few recent releases of NPSS. IDE development continues with an external release expected in late 2018.


The third project area for the NPSS consortium at this time is models, elements and interfaces (EMI). The focus of this project is to independently manage, maintain and develop the engineering functions associated with NPSS. The models in this project are intended to be demonstration models for use in training or in the development of new, similar models. For example, there are engine cycle models, a fuel system model (in development) and a mission analysis model. These models are currently available to consortium members only.

The elements are the engineering code that define the behavior of various cycle components such as a compressor, a burner or a turbine. These elements have traditionally been maintained with the core development program, but are now maintained and configuration controlled separately. In this way, element updates can occur without a new release of the Core. Interfaces are important for sharing NPSS models with others and/or using them interactively with other design tools that are commercially available. The intent of this area is to provide clear documentation and examples of making these interfaces work so that NPSS developers can support various design studies as the models are integrated in with other optimization tools, etc.

How to Get NPSS

You can now purchase an NPSS license online through this website. Because NPSS is export controlled, the sale of NPSS licenses is restricted to countries not currently listed on the U.S. Dept. of Commerce Anti-Terrorism watch list. Visit our NPSS License page for more details and to purchase NPSS.

To contract with SwRI, please contact the Machinery Services Hotline at +1 210 522 3000.

For more information, contact Charles Krouse or call +1 210 522 5001.