A new approach to DSMC collision modelling, called viscosity-DSMC or µ-DSMC, is described in which the time-averaged temperature is used to set the characteristic collision cross-section in each cell such that the Chapman-Enskog viscosity is that given by any desired viscosity law µ = µ (T ), including a curve fit to experimental data. For example, a hard sphere collision model, with hard sphere collision probability, used with a different molecular size in each cell can reproduce a Sutherland

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... iscosity law. Similarly, a variable hard sphere collision model can reproduce the viscosity given by the more complicated generalized hard collision model, by making the reference cross-section a function of the temperature. This model is used to calculate the structure of a plane 1D shock and the results agree closely with those from standard DSMC using the GHS model. A particularly simple method is to use the Maxwell VHS model, in which all collision pairs are equally likely, to produce any desired viscosity law. The time-averaged cell temperature is available in standard DSMC as part of the procedures which determine the steady state flow and the new methods are as fast as, or faster than standard DSMC. Unlike more complicated models with realistic viscosities, the new procedures are compatible with the Borgnakke-Larsen energy exchange scheme and the established chemistry models for DSMC. CP762, Rarefied Gas Dynamics: 24 th International Symposium, edited by M. Capitelli © 2005 American Institute of Physics 0-7354-0247-7/05/$22.50 Report Documentation Page Form Approved OMB No. 0704-0188 Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number.