pat no 6 861 025 to breister et al and is adequate for the production of meltblown fabrics at low and moderate speeds of collection belt 26 however as the process is run harder and faster e g after the production of fabric exceeds approximately 35 g hour hole difficulties arise in the form of erratic motion imparted to some of the emerging filaments at higher extrusion rates the orderly accumulation of filaments upon collection belt 26 becomes disrupted and some filaments begin to collect upon the surface of die 22 and on the ducts 40 and 42 this observation suggests that paired areas of recirculation taking the form of standing vortices had formed roughly at the positions marked a and b in that it is desirable to be able to increase line speed while maintaining the desirable properties of the fabric 34 and in that disrupting the posited recirculation zones a and b seem likely to be amenable to solution by a gas dispensing manifold that is elongated in the direction perpendicular to the two dimensional representation of fig1 an initial geometrical representation was set up according to fig2 a simplifying assumption was made that the problem was symmetrical in spite of the recognized complication that the collection belt 26 in fig1 is in motion and does generate some fluid motion by the no slip condition the existing geometry of the cavity 28 in fig1 the duct 42 in fig1 and collection belt 26 in fig1 are represented virtually as geometric representations 28 v 42 v and 26 v respectively boundary conditions are set as being the known gas pressures that provide the best albeit inadequate operating conditions when collection belt 26 is operated.