Aerodynamic heating in hypersonic flows

For the last quarter of 20th century, Concorde airliners and other supersonic aircraft shuttled wealthy passengers between North America Europe at speeds up to 600 m/s (about 1350 mph). The planes were retired in 2003. They had grown prohibitively expensive worried passengers, who couldn’t help but notice that planes’ windows too hot touch.Today, however, several airlines have plans reinstate jets capable (Mach 1) hypersonic 5) speeds—the Mach number is ratio a plane’s speed local sound. 5 routinely exceed 1500–2000 m/s, depending on their altitude. A jet fast could fly from New York Paris just 90 minutes.Technical challenges forestalled development. temperature air passing over increases with has been measured 2200 K surface plane flying an altitude 20 km. Understanding where when those high temperatures occur critical its performance safety. This Quick Study explores newly discovered mechanism can reduce heating jet’s surface.From laminar turbulentSection:ChooseTop pageABSTRACTFrom turbulent <<Hypersonic heatingEngineering coolAdditional resourcesCITING ARTICLESAccording conventional wisdom, aerodynamic peaks onset turbulence. Its emergence substantially shear stresses adjacent surface, process converts kinetic energy heat. Figure 1 visualizes boundary layer—the thin layer whose flow decelerates zero aircraft’s bounding surface. transition turbulence, which due amplification air’s velocity pressure instabilities, unavoidable as rises.Figure 1. Rayleigh scattering reveals layer. Airflow left right 6 tunnel. high-frequency wave region eventually results turbulence right. (Adapted C. Lee, S. Chen, Natl. Sci. Rev. 6, 155, 2019, doi:10.1093/nsr/nwy052.)PPT|High resolutionThe image, obtained low-temperature wind tunnel, produced by laser carbon dioxide gas mixed upstream air. In cold above layer, solidifies into fine particles. But inside are much higher because dissipation, CO2 remains gaseous. Light particles appears white, whereas gaseous black. airflow, initially well ordered right, thus seen become compression expansion produce amplifying acoustic wave.The hottest turbulent. Surprisingly, though, recent studies shown comparable peak also develop prior transition. IR figure 2a, flared cone wind-tunnel experiments run bears out. pre-turbulent peak, labeled “SH” for secondary heating, develops otherwise lower-temperature (TH).Figure 2. rises tunnel flowing 6. (a) An camera captures two (yellow) spots: one (SH) arises air-compression effects, followed second (TH) shearing stresses, or turbulence-induced friction. blue SH TH result cooling expansion. Blue dots signify flush-mounted sensors. Y. Zhu et al., Phys. Fluids 30, 011701, 2018, doi:10.1017/jfm.2018.646.) (b) Surface within imaged without (top) (bottom) acoustic-wave control introduced leading edge cone. (Courtesy Cunbiao Lee.) video effect, see below.Download Original Video (3.2 MB)https://aip-prod-streaming.literatumonline.com/journals/content/pto/2021/pto.2021.74.issue-11/pt.3.4888/20211022/media/pt.3.4888.mm.original.v1.,773,645,.mp4.m3u8?b92b4ad1b4f274c70877518510abb28b4b52684e04957b0ffa32428805db72bf1ae006baafd3547213af4e27a9ba4ba3a3bc479a51b703c971d162395b98752ca5e3368acbf3273ae813b111a4769aef3c0c42f3997c84a88c9abec0bfd3291bd5e6819d046e61af2ebfaebc26c3b998c8d5935c3293ca85442cbedd2982a9bae00235475ddef42c84c83756b875836bec07152b7af7c7349f036f4e20106cd78b77610ePPT|High resolutionThat was first identified three years ago Lee his colleagues China’s Peking University. Their research revealed previously unidentified alternative interaction—one either increase circumstances.Hypersonic heatingSection:ChooseTop turbulentHypersonic <<Engineering ARTICLESWhat accounts separate peaks? Three mechanisms convert mechanical thermal flow. viscous dissipation normal acting compressed And third work done changes air.The conversion unidirectional—from energy—so they always dissipate Thus, high-shear accompany heat 2a example.But occurs caused work. Numerical simulations magnitude direction depends phase differences periodic fluctuations air-density upshot bidirectional: It augment diminish sign differences.Engineering coolSection:ChooseTop cool <<Additional ARTICLESPressure behave waves, phenomena known second-mode waves. Although fluctuating waves normally same frequency wave, differences—that is, peak—can vary. So (their coincident), will be positive heating. out opposition), negative Lee’s group it recognized year new Bohua Sun Xi’an University Architecture Technology China Elaine Oran Maryland College Park.The flows behaves controllable using porous wavy Sound absorption modify difference enough eliminate 2a. Alternatively, use appropriately generate modifies natural how heats surface.Figure 2b shows images typically observed. When no applied cone, upper panel exhibits large (yellow). contrast, essentially disappears lower near general, roughly 25%.Through series detailed studies, demonstrated fundamental behavior transitions flows, mechanism, developed successful strategies controlling it. Through understanding relationship different types physical basis certain aspects high-Mach-number emerged. How future seen.Additional resourcesSection:ChooseTop resources <<CITING ARTICLES? “Recent progress study layer,” 155 (2019). https://doi.org/10.1093/nsr/nwy052, Google ScholarCrossref? “Newly principle flows,” J. Fluid Mech. 855, 152 (2018). https://doi.org/10.1017/jfm.2018.646, “Acoustic-wave-induced turbulence,” 32, 061702 (2020). https://doi.org/10.1063/5.0011871, ScholarCrossref, ISI? B. Sun, E. Oran, “New heating,” 5, 606 https://doi.org/10.1093/nsr/nwy035, W. “Experimental permeable wall cone,” 011701 https://doi.org/10.1063/1.5139546, ScholarScitation© 2021 American Institute Physics.