NASA/ASEE SUMMER FACULTY FELLOWSHIP PROGRAM

ABSTRACTSupersonic nozzles which operate at low Reynoldsnumbers and have large expansion ratios have very thickboundary layers at their exit. This leads to a very strongviscous/inviscid interaction upon the flow within the noz-zle and the traditionalnozzle design techniques whichcorrect the inviscid core with a boundary layer displace- .... _ L_ ment do not accurately predict the nozzle exitIn addition, if the nozzle exit density becomes low enoughrarefaction ^;;_ 4" _h_ fnrm nf velocity slid and tem-perature jump at the wall must be accounted for.The present work Qsed a full Navier-Stokes code(PARC2D) to compute the nozzle flow field. Grids were gen-erated using the interactive grid generator code TBGG. Allcomputations were made on the NASA MSFC CRAY X-MP computer.Comparison was made between the computations and in-housewall pressure measurements for CO 2 flow through a conicalnozzle having an area ratio of 40. Satisfactory agreementexisted between the computations..and measurements for astagnation pressure of 29.4 psia and stagnation temperatureof 1060 °R. However, agreement did not exist at a stagna-tion pressure of 7.4 psia. Several reasons for the lack ofagreement are possible. The comPutational code assumed aconstant gas gamma whereas gamma for CO 2 varied from 1.22in the plenum chamber to 1.38 at the nozzle exit. The com-putations were performed assuming adiabatic, no-slip walls,both of which may not be correct. Finally, it is possiblethat condensation occurred during the expansion at thelower stagnation pressure. The next phase of the workwill incorporate variable gamma and slip wall boundaryconditions in the computational code.XV-i