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Next: Choking explanation for pressure Up: Working Conditions Previous: Fanno Flow Supersonic Branch Index The Pressure Ratio, P2/P1, effectsIn this section the studied parameter is the variation of the back pressure and thus, the pressure ratio variations. For very low pressure ratio the flow can be assumed as incompressible with exit Mach number smaller than . As the pressure ratio increases (smaller back pressure, ), the exit and entrance Mach numbers increase. According to Fanno model the value of is constant (friction factor, , is independent of the parameters such as, Mach number, Reynolds number et cetera) thus the flow remains on the same Fanno line. For cases where the supply come from a reservoir with a constant pressure, the entrance pressure decreases as well because of the increase in the entrance Mach number (velocity).Again a differentiation of the feeding is important to point out. If the feeding nozzle is converging than the flow will be only subsonic. If the nozzle is ``converging-diverging'' than in some part supersonic flow is possible. At first the converging nozzle is presented and later the converging-diverging nozzle is explained.
Subsections Next: Choking explanation for pressure Up: Working Conditions Previous: Fanno Flow Supersonic Branch Index Created by:Genick Bar-Meir, Ph.D. On: 2007-11-21 |