Rho vee aaaah 0 = [ V A ] incoming + [ V A ] outgoing For steady - PowerPoint PPT Presentation

Rho vee aaaah 0 = Σ [휌 V ⟂ A ] incoming + Σ [휌 V ⟂ A ] outgoing For steady flow through a fixed volume. 1|10

Danger (휌| V ⟂ | A ) 1 = (휌| V ⟂ | A ) 2 “if A increases, then V must decrease” oder? 2|10

Photo US Navy (1961, public domain) 3|10

Photo CC-by-sa by Airwolfhound 4|10

Photo by Lori Losey / NASA (public domain, 2007) 5|10

Rolls-Royce Spey Photo CC-by-sa Arjun Sarup 6|10

Possibly Wrong Fluid Mech 1 only true if 휌 remains constant. OK for water fl ows. No heat transfer, no expansion! Supersonic fl ow: A ↘ can lead to V ↘ because 휌 ↗ . 7|10

Smaller A, larger V? Photo CC -by by Amy Stanley 8|10

Possibly Wrong Fluid Mech 2 There is no causal relationship. A 2 ↘ may mean V 2 ↗ , but... nothing guarantees A 2 V 2 remains constant! (maybe ̇ m ↘ ). Increases in velocity are not “for free”: they require force be applied and energy be spent. 9|10

Are you using the mass balance equation to predict velocity? → also ask yourself: what force, what power required? 10|10