A SINGLE INTERNAL WORKING SURFACE IN A PERIODIC JET

We present the numerical simulation of a single internal working surfa ce which farms along the body of a supersonic jet with periodic variat ions in the magnitude of its velocity. The structure, the evolution an d the observational properties of this flow are analysed. We make a qu alitative comparison with previous analytic predictions, simulations o f the complete jet and observations of Herbig-Haro jets. The apparent lag of the knots of emission with respect to the jet flow (which has b een observed in some jets) can be explained by this model.