School of Aerosace Engineering Suersonic (Engine) Inlets For air-breathing engines on suersonic vehicles, usually want to slow flow down to subsonic seeds inside engine need diffuser (M>1 M<1) for engine inlet excetion: suersonic combustion (e.g., SCRAM jets) Goal lowest o loss (highest thrust) given flight M mass flow rate requirement (thrust) stable oeration (nothing drastic for small changes in flight conditions) Suersonic Inlets - Oblique Shocks -1 Coyright 2001 by Jerry M. Seitzman. All rights reserved. School of Aerosace Engineering CD Inlet Can get close to isentroic flow lowest otential o loss starting roblem (like suersonic wind tunnel, have to swallow shock) M>1 M<1 most cases requires variable area throat (heavy, comlex) stability roblem: if shock leaves throat, can exit engine lowering mass flow (higher A 2* ) Not tyically used Suersonic Inlets - Oblique Shocks -2 Coyright 2001 by Jerry M. Seitzman. All rights reserved. 1
Suersonic Inlets - Oblique Shocks -3 Coyright 2001 by Jerry M. Seitzman. All rights reserved. School of Aerosace Engineering Shock Inlets Normal shock diffuser simle, diverging section receded by normal shock highest o loss (strong shock) Oblique Shock Diffuser oblique shock(s) followed by normal shock at (or inside) inlet to subsonic diffuser lower o loss works for range of M Normal Shock M>1 Oblique Shocks Normal Shock M<1 Silled Air Silled Air ByassAir Subsonic Diffuser Bleed Air School of Aerosace Engineering Examle: Normal v. Oblique Diffusers Given: You need to ick a diffuser for Mach 2 flight conditions. Your choices are a normal shock diffuser and 2 different oblique shock diffusers Find: Stagnation ressure loss for each ( o,final / o,initial ) Assume: air is TPG/CPG with γ1.4, steady, adiabatic, no work, inviscid excet for shock,. M2 o,initial M2 o,initial M2 o,initial 5 o,final o,final o,final Suersonic Inlets - Oblique Shocks -4 Coyright 2001 by Jerry M. Seitzman. All rights reserved. 2
School of Aerosace Engineering Solution: Normal v. Oblique Diffusers Analysis: Normal Shock Diffuser M1 2 M2 0.577, o2 o1 0.721 Single Oblique Shock (+Normal) M 1 1 n M sin θ 2sin 39.3 1.267 0.803; 0.985 Suersonic Inlets - Oblique Shocks -5 Coyright 2001 by Jerry M. Seitzman. All rights reserved. Table B.1 or VII.11,13 VII.26 or C.1 M 1 2, δ 10 θ 39.3 B.1 or VII.11,13 M2 n o2 o1 ( θ δ) 1. 64 M2 M2n sin M3 0.657; o3 o2 0.880 B.1 or VII.11,13 M 1 2 o1 M 1 2 o1 M 2, o2 M 2, o,2 M 3, o3 o3 o3 o2 0.867 o1 o2 o1 normal shock inlet - 28% o loss oblique shock inlet - 13.3% o!!! School of Aerosace Engineering Solution: Normal v. Oblique Diffusers Analysis: (con t) Two 5 Turns (+Normal Shock) Suersonic Inlets - Oblique Shocks -6 Coyright 2001 by Jerry M. Seitzman. All rights reserved. M 2, o,2 M 3, o3 VII.26 or C.1 M2 5 M1 2, δ1 5 θ1 34.3 o1 M1 n M1 sin θ1 2sin 34.3 1.127 B.1 or VII.11,13 M2 n 0.891; o2 o1 0.998 M2 M2n sin( θ1 δ1) 1. 82 o4 o4 o3 o2 VII.26orC.1M2 1.82, δ2 5 θ2 37.9 o1 o3 o2 o1 M2 n M2 sinθ2 1.82sin 38.0 1.120 0.873 B.1 or VII.11,13 M3 n 0.897; o2 o1 0.998 double obl. shock inlet M3 M3n sin( θ2 δ2 ) 1. 65 ~ 12.7% o loss B.1or VII.11,13 M3 0.654; o4 o3 0.8765 3
School of Aerosace Engineering Double Oblique Inlet - Advantages So for M2, same total turning angle () two oblique shocks slightly better than one (12.7% v. 13.3% o loss ) significant imrovement over normal shock alone (28% o loss) Oblique shock diffuser with two turns (total δ of ) even better only 4.3% o loss (solution shown on next slide) so larger overall deflection can give better o Stagnation ressure advantages of using multile oblique shocks increase with higher M Suersonic Inlets - Oblique Shocks -7 Coyright 2001 by Jerry M. Seitzman. All rights reserved. School of Aerosace Engineering Double Oblique Shock Diffuser Two Turns (+Normal Shock) M 2, o,2 from revious results for turn M1 2, δ 10 θ1 M2 1.64; o2 o1 B.1 or VII.11,13 34.3 0.985 VII.26 or C.1M2 1.64, δ2 10 θ2 M2 n M2 sin θ2 1.64sin 49.4 B.1 or VII.11,13 M n 0.815; o2 o1 ( θ δ ) 1. 28 M M3n sin 2 2 3 49.4 1.245 3 M2 M3 0.796; o4 o3 0.983 0.988 o1 o4 o1 M 3, o3 o4 o3 0.957 o3 o2 o2 o1 Suersonic Inlets - Oblique Shocks -8 Coyright 2001 by Jerry M. Seitzman. All rights reserved. 4
School of Aerosace Engineering Double Oblique Inlet - Disadvantages Flow searation since increases across oblique shocks, the flow sees adverse gradient so more or bigger oblique shocks (or longer external ram), Suersonic Inlets - Oblique Shocks -9 Coyright 2001 by Jerry M. Seitzman. All rights reserved. Oblique Shocks Normal Shock Boundary Layer Silled Air Bleed Air the greater the chance the boundary layer will searate major change in flowfield, large losses ( o and mass flowrate) Internal Turn Angle larger total external turn angle showed less o loss larger external flow turning requires larger inlet also requires larger internal flow turning to get flow back to horizontal ByassAir Subsonic Diffuser 5