![]() NPR plot below shows no abrupt change in feed conditions Time window for pressure histories.Overall, shows decrease in pressure fluctuations in 2nd structure.Each line reflects pressure at tap indicated by similarly colored diamond.Flow structure change visible in pressure histories as well.Shock abruptly moves aft along plug (and forward along shroud) as NPR slowly increases past 2.05 Placement in time shown here 75 s 60 s.Pressure distributions show this structure change.(Recorded at 100 fps, playback at 1/10th speed).Shows distinct asymmetry in 2nd structure.Abrupt change in flow behavior & shock train at NPR of roughly 2.05.Near NPR 2.50, wide band of pressure oscillation frequencies, but no distinct peaks (repeatable during 3 distinct tests).60 Hz noise seen in many hot fire tests.Spectrum for f > 1000 Hz caused by combustion instabilities.Frequency peaks in same 200-400 Hz range, not as evident as with cold flow.Unsteady behavior beyond dynamic transducers for NPR ≥ 2.59.Substantial pressure oscillations at NPRs ≤ 2.25 due to shock movement.Comparison near throat shows why two pressure taps are suspect CFD – solid lines Experimental – discrete data points.This CFD does not resolve the boundary layer well.Conclusion: flow is dominated by boundary layer and separation.Most glaring difference is axial shock location.Fluent analysis with coarse unstructured grid for sizing.Caused by temperature difference of roughly 800-1000☏ Separation Shocks *only viewing 45° taps.Primary difference between hot & cold operation is position of shock along plug.Black/yellow diamonds indicate suspect data points.Can clearly see shock locations, separation regions.Steady Pressures: Experimental Comparisons Very good match with dynamic pressure transducers.Axisymmetric CFD shows that a large separation region does exist and that the faint normal shocks do not extend all the way to the plug surface Cold Flow, NPR 1.88 Hot Fire, NPR 2.03 (courtesy DheerajKapilavai).“Wavy” shape of apparent shocks is uncharacteristic of normal shocks.No shock reflection or separation on plug.After 1st hot fire, some condensed liquid accumulated on the shroud’s inner surface, forming a visualization of shock location at the wall typical of oil flow Cold, NPR 2.45 Cold, NPR 2.14 Hot, NPR 2.03 Hot, NPR 2.39 Hot, NPR 2.93.Optical properties of glass shroud prevented schlieren use.Mixing layer between hot core and cold bypass streams not very clear due to light path integration issue NPR 2.50 NPR 3.48 Mixing Layer Edge Sample Expected Mixing Layer Image v1, ρ1 NPR 4.47 NPR 6.12 v2, ρ2.Quality schlieren images harder to obtain during hot fires due to combustion products and temperature gradients.At cruise, shroud trailing edge shock lies right at theoretical plug tip.Schlieren and Shadowgraph techniques integrate along the optical path – for axisymmetric flow, this results in “phantom” shock patterns (dotted lines) LEGEND Horizontal Knife-Edge Vertical Knife-Edge Cold 3.70 (approx.) Cold 3.73 Cold 2.45 ShadowgraphĬold Flow Schlieren NPR 1.40 NPR 1.88* NPR 2.23 *discussed in detail later NPR 3.06 NPR 3.73 NPR 5.75.Higher NPRs setup classic diamond-shock pattern in exhaust.Classic lambda shock forms on both plug and shroud wall.Little asymmetry (x/L = 0.52 again) Playback at 1/10th speedĭetailed Data Comparisons & Additional Analysis.Plug design has also been shown to be less noisy Plug Nozzle at NPR 1kHz shows combustion frequencies.Can truncate plug to get net increase in performance.Pressure plot at right shows better performance for plug at low NPR.Consider thrust as integral of surface pressure over projected area.Shocks/expansions are the mechanisms that enable altitude-compensation.For NPRs at and above design, behaves like standard C-D nozzle.For NPRs below design, avoids overexpansion.Free jet boundary expands to match local ambient pressure.Plug nozzles are altitude-compensating.Plug nozzle design chosen for easy integration with this concept Flow Flow Gulfstream High-Flow Bypass Concept.Zero-energy-added stream only intent is to reduce losses.High-flow bypass region avoids thick engine nacelle that would create strong shock wave.Test geometry derived from Gulfstream’s High-Flow Bypass concept.Provide basis for CFD comparison & evaluation.Characterize behavior, especially low nozzle pressure ratio (NPR) unsteady effects.Research carried out under Task 7c of the Supersonic Business Jet program (SSBJ).Experimental static test of plug nozzle.John SullivanĬAD Model Schlieren Installed Hardware Static Pressures Shadowgraph Dynamic Pressures Experimental Aerodynamic Analysis of a Plug Nozzle for Supersonic Business Jet Application John Tapee Dr.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |