#n225nn

[sentinelchicken]

An Embraer E175 of Envoy/American Eagle, N225NN, heads out for departure at DFW. ⠀ ⠀ Note the engine nozzle chevrons on the GE CF43-8E5 engines. Unlike the 737MAX and 787 that have the engine noise reducing chevrons on the fan cowling, the E175 has them on the hot section nozzle as does the CRJ900 (the 747-8 has them on both the hot section and fan cowling). ⠀ ⠀ Now we’re going to get into a little aeroacoustics here, so take notes. ⠀ ⠀ Jet exhaust noise comes in two forms- turbulent mixing noise and shock noise. Turbulent mixing noise comes from the high speed jet exhaust’s boundary with slower surrounding air creating turbulence and turbulence creates noise. Chevrons on the fan cowling as well as the hot section nozzle speed the mixing of the air which dampens turbulence and lessens noise. ⠀ ⠀ Shock noise, however, comes from the speed of the jet exhaust moving near the speed of sound and it creates shockwaves in the exhaust (the afterburner shock diamonds from high performance jets is a perfect visualization of those shockwaves). Sometimes those shockwaves interact with the turbulent flow and this creates a self-propagating acoustic wave. ⠀ ⠀ This wave we perceive as a high pitched whine and it’s called jet screech. Hot section chevrons like on the CF34 engine here also break the self propagation of the jet screech acoustic wave, dampening high pitched sounds from the jet exhaust. ⠀ ⠀ Got it? There’s gonna be a test next week on this.⠀ ⠀ #Avgeek #aviation #aircraft #planeporn #KDFW #DFW #airport #igTexas #planespotting #airlines #Embraer #E170 #American #AmericanAirlines #AmericanEagle #EnvoyAir #DFWavgeek #instagramaviation #N225NN #splendid_transport #instaaviation #aviationlovers #aviationphotography #flight #aviationphotography #AvgeekSchoolofKnowledge #AvGeeksAero #AvGeekNation (at DFW Airport) https://www.instagram.com/p/B5HId6-BJGa/?igshid=6676jfg1uigf