VORTEX SHEDDING FROM SOLID ROCKET MOTOR PROPELLANT INHIBITORS (FREQUENCY, COMPUTATIONAL FLUID DYNAMICS)

A mathematical model is presented for investigating the vortex shedding caused by the protrusion of inhibitors into the flow field of a solid rocket motor (SRM). The principal objective of the research is the theoretical determination of the vortex shedding frequency. For the model, the time-dependent Navier-Stokes equations are solved with the assumption of incompressible, two-dimensional flow using a finite difference technique. For laminar flow, explicit solutions are obtained using a vorticity-transport equation in place of the Navier-Stokes equations. A two-equation ((kappa)-(epsilon)) model is used for turbulence modeling. The solutions are obtained from primitive equations using a semi-implicit, pressure-correction method.; To verify the theoretical results, cold flow tests were conducted to determine experimentally the vortex shedding frequency under both laminar and turbulent flow conditions. The laminar flow experimental model is two-dimensional and was tested at Reynolds numbers from 2.72 x 10('4) to 8.05 x 10('4) in the Auburn University smoke tunnel. The turbulent flow model is an axisymmetric 2.6% scale model of a section of the Space Shuttle SRM containing circular perforated grain segments and inhibitors made to simulate the geometry after 80 seconds of burning. This model was tested in the Auburn University supersonic wind tunnel test facility at Reynolds numbers from 2.45 x 10('5) to 5.97 x 10('5). For both laminar and turbulent flow models, the vortex shedding frequencies were determined using a stroboscope and yarn tufts fastened to one inhibitor. Upstream conditions were measured by hot wire and hot-film anemometers for laminar and turbulent flow, respectively.; The vortex frequencies measured compared favorably with those obtained from the mathematical model. The range of these frequencies was about from 5 HZ to 30 HZ. The frequencies were sensitive to upstream turbulence intensity. The location of the vortex shedding, which existed behind the inhibitors of the experimental models agreed reasonably well with predictions from the mathematical models for both laminar and turbulent flow.