{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"3fc7c3c01db868faa485e8481773710a7f05aaa0892b6096f102cad0c642d505","created":"2026-10-15T23:43:22Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["ce59fb6cd812fc05906d0c60a71c75ea22bc686bcf38e7c3ef7010834d98ee7b","f65ad5573805b868449f3e52ead6a433262d6e32c0e5015c17cc573e196f1f62"],"salt":"ff1c132c6d18d59e5f010628f838987ae39e3852ec4cb980e90d722793605882","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"mechanism","assisted_by":[],"external_id":"fluid.turbulent-combustion.unconfined-ddt","kind":"well-posed","literature_status":"contested","n":"2","parents":[],"plain":"A flame (deflagration, burning that spreads slower than sound) usually needs walls or obstacles to build up into a detonation. Simulations suggest that strong turbulence alone can do it in open space; does this happen in real gas mixtures, and by what route?","posed_since":"","precise":"For a premixed fuel-air flame (for example stoichiometric $\\mathrm{H_2}$-air or $\\mathrm{CH_4}$-air) in homogeneous isotropic turbulence with no walls or obstacles, determine whether deflagration-to-detonation transition (DDT) occurs, and the threshold in turbulent intensity $u'/S_L$ and integral scale $L/\\delta_L$ ($S_L$ laminar flame speed, $\\delta_L$ laminar flame thickness). Test the proposed route in which the turbulent flame speed exceeds the Chapman-Jouguet deflagration speed (the fastest steady deflagration allowed by conservation laws), so pressure builds up in the flame brush and forms shocks that trigger detonation. An answer is a verified criterion for unconfined DDT as a function of mixture and turbulence.","problem_ref":"f65ad5573805b868449f3e52ead6a433262d6e32c0e5015c17cc573e196f1f62","references":"","settled_by":"Experiments with turbulent premixed flames free of walls and obstacles that observe or exclude DDT at controlled $u'/S_{L}$ and $L$, matched by fully resolved simulations with detailed chemistry.","status_note":"Simulations published in 2019 support the route in which the turbulent flame speed exceeds the Chapman-Jouguet deflagration speed; channel experiments up to 2025 are consistent with it, but no test free of walls and obstacles exists, and only a few mixtures have been tested.","title":"Can turbulence alone turn an unconfined premixed flame into detonation?","topic_ref":null},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"e3d2b6c174b2023c5d485f0f27f2f153d93a06e64dda931420c9f26c3d3250ec","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"827ec5f413e5416358b948cc02fdbc7351a74824767e5cb5792194260d724072","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"61ZvuPL_UVypcUguXoEu6-aeEb7WQClGMoe324QY_bf8kD1p7MdjF6X7IaYLdn0qwA7exvRcaEAOmaQRI3q2Aw"},"schema":"pubphys.envelope/1"},"record_hash":"e3d2b6c174b2023c5d485f0f27f2f153d93a06e64dda931420c9f26c3d3250ec","leaf_index":3288}