BEGIN:VCALENDAR VERSION:2.0 PRODID:-//wp-events-plugin.com//7.2.3.1//EN TZID:Asia/Jerusalem X-WR-TIMEZONE:Asia/Jerusalem BEGIN:VEVENT UID:0-1645@aerospace.technion.ac.il DTSTART;TZID=Asia/Jerusalem:20260603T133000 DTEND;TZID=Asia/Jerusalem:20260603T143000 DTSTAMP:20260519T105315Z URL:https://aerospace.technion.ac.il/events/pavel_galich_3june26/ SUMMARY:Colloquium: Phononic crystals for passive hypersonic flow control DESCRIPTION:Lecturer:Pavel Galich\n Faculty:The Stephen B. Klein Faculty of Aerospace Engineering \n Institute:Technion – Israel Institute of Techn ology\n Location:Classroom 240\, 1st floor\, Aerospace Eng. building\n Zoo m: https://technion.zoom.us/j/98372598857\n Abstract: Hypersonic flight is governed by strongly coupled aerothermodynamic\, acoustic\, and structura l phenomena. Among the central challenges is the onset of boundary-layer t ransition\, which can substantially increase skin-friction drag\, wall hea t flux\, and unsteady loading. In cold-wall hypersonic boundary layers\, t ransition is often dominated by Mack’s second mode\, a high-frequency in stability whose physical character is primarily acoustic\, or thermoacoust ic\, in nature. Because this mode may be interpreted as an acoustic distur bance trapped within the boundary layer\, its amplification is inherently sensitive to the dynamic response and effective impedance of the wall. Thi s observation motivates the use of phononic subsurfaces as passive\, struc turally integrated mechanisms for frequency-selective flow control.\n\nIn this colloquium\, I will present our recent work on bandgap formation in t wo-dimensional solid–void phononic crystals with four-fold rotational sy mmetry. The discussion will focus on experimentally realizable architectur es belonging to the p4\, p4mm\, and p4gm plane groups. Using Bloch–Floqu et band-structure analysis\, evanescent-mode calculations\, finite-size tr ansmission-loss simulations\, and ultrasonic experimental validation\, I w ill show how Bragg scattering and local resonance can become strongly coup led to produce exceptionally wide complete bandgaps. Attention will be giv en to the roles of resonator size\, ligament slenderness\, and crystallogr aphic symmetry in controlling attenuation of both longitudinal and transve rse elastic waves.\n\nI will then discuss how these bandgap mechanisms can be translated toward passive hypersonic flow control. The proposed concep t is to embed single-phase metallic or ceramic phononic subsurfaces beneat h an aerodynamically smooth wall\, thereby targeting the ultrasonic freque ncies associated with Mack’s second mode without introducing surface rou ghness or requiring external actuation. This approach is intended to combi ne the spectral selectivity of phononic cystals with the thermal robustnes s and mechanical integrity required for hypersonic environments. The talk will conclude by outlining a research path toward compact phononic subsurf ace inserts (less than 2 cm!) with bandgaps in the approximate 50–200 kH z range\, suitable for future cone–flare experiments and for the broader development of passive transition-delay strategies in hypersonic flight.\ n Details: \n CATEGORIES:Seminars LOCATION:Classroom 240\, 1st floor\, Aerospace Eng. building END:VEVENT BEGIN:VTIMEZONE TZID:Asia/Jerusalem X-LIC-LOCATION:Asia/Jerusalem BEGIN:DAYLIGHT DTSTART:20260327T030000 TZOFFSETFROM:+0200 TZOFFSETTO:+0300 TZNAME:IDT END:DAYLIGHT END:VTIMEZONE END:VCALENDAR