Kareem A. Ahmed’s research while affiliated with Central Florida College and other places

... However, achieving sub-micron resolutions in three-dimensions becomes computationally demanding and next-to-infeasible on very large computational domains. Therefore, to keep the computations feasible while ensuring adequate resolution across the induction zone, we shift to the shock-frame of reference (SFR) [11,12]. For an in-depth analysis on the equivalence of the shock and lab-frames of reference and the correctness of the shock-frame, readers are referred to our other AIAA SciTech 2025 paper focused on this aspect [11]. ...

Reference:

Three-Dimensional Micro-Jetting Dynamics in a Stoichiometric H 2 /Air Detonation

... Three droplet sizes of 5, 10, and 20 µm are chosen to investigate the effect of droplet diameter on the resultant detonation properties. The [52,53]. It will be shown below that the obtained detonation cell sizes are smaller than the channel height, even for the largest droplet size. ...

Reference:

Numerical Simulations of Non-Ideal Spray Detonations in Jet Fuels With a Shock-Droplet Interaction Model

... In two-phase detonations, hypersonic shocks impact liquid fuel droplets, causing fragmentation, vaporization, and mixing of fuel with air. Experimental studies [4] indicate that upon shock impact, droplets of water or hydrocarbons flatten (i.e., the "pancaking" deformation) and vaporize quickly along their perimeters. Proposed fragmentation mechanisms include Rayleigh-Taylor piercing and shear-induced entrainment [5]. ...

Reference:

Simulation of Shock-Droplet Interactions at Detonation-Relevant Conditions Using Vapor-Liquid Equilibrium Theory

... Available KHRT parameters in published literature are primarily calibrated for either the primary atomization of a liquid column jet or diesel spray injection. Using these default parameters for detonation-droplet interactions yield droplet lifetimes that are two orders of magnitude smaller than what is observed in experiments [21][22][23]27]. The child droplets generated are significantly smaller than expected. ...

Reference:

Detonation-Droplet Interaction Simulations Utilizing the Lagrangian KHRT Breakup Model

... Prevalence of high dimensional non-linear systems in aerospace engineering(Pan and Johnsen, 2017;Yu, 2012). ...

Reference:

Robust and Interpretable Learning for Operator-Theoretic Modeling of Non-linear Dynamics

... Many studies have been conducted on the secondary atomization (breakup) of droplets colliding with non-reacting shock waves [8][9][10][11][12][13][14][15]. There are many similarities between shock-droplet and detonation-droplet interactions, but fundamental differences in the physics of detonation-droplet interactions require additional attention, especially for RDREs [16]. ...

Reference:

Detonation-Droplet Interaction Simulations Utilizing the Lagrangian KHRT Breakup Model

... Meanwhile, to overcome the challenges posed by liquid fuel detonation initiation and sustainment, there have also been studies on exploring the physics of multi-phase rotating detonations. [22][23][24][25][26][27][28][29][30] Advanced diagnostic techniques like chemiluminescence imaging, 31 planar laser-induced fluorescence (PLIF), 32 and high-speed schlieren 33 and optical imaging 34 have also been used for visualization of the supersonic rotating detonation flow field. ...

Reference:

Rotating detonation combustor with regional full-coverage film cooling and variable-shaped hole arrangements

... The pressure gain effect and rapid heat release associated with detonations also reduce engine complexity and weight, enhancing the thrust-to-weight ratio and reducing fuel consumption. As a result, RDE research has expanded globally, leading to innovations in rotating detonation rocket engines, [3][4][5][6][7][8] airbreathing propulsion systems, [9][10][11][12] and gas turbine integrations. [13][14][15][16][17][18][19][20][21] Recent advancements include hot-fire tests of a 7000-pound-force RDE 4 and the development of sounding rockets using liquid 6 and gaseous 5 propellants. ...

Reference:

Rotating detonation combustor with regional full-coverage film cooling and variable-shaped hole arrangements

... contours for an strut-baesd combustor with expansion (z = 0.0012 m) [ in the Zhang's study [20] 如图 6 所示的波瓣支板后缘的波瓣结构同样 能够增加流动扰动促进燃料混合，因此也被一些 研究采用 [21,22] [39] Fig. 15 Schematic diagram of cavity flow field structure [39] Wang 等 [40] 通过实验探究了凹腔在燃烧室中 的作用，发现没有凹腔构型时，燃烧室内无法实 现稳定燃烧，凹腔起到了火焰稳定器的作用，且 任何促进燃料进入凹腔剪切层和凹腔回流区的方 法都可以使燃烧向更稳定的模式转变。因此，凹 腔可以被认为是超燃冲压发动机燃烧室中重要的 火焰稳定装置。Cai [41] 、Choubey [42] 等曾分别对凹 腔的点火研究和发展动向进行过总结与归纳。 Hammack 和 Ombrello [43] [44] Fig. 16 Flame base stabilization locations [44] Ribeiro 等 [45] Lean premixed (blue), rich premixed (red) and non-premixed (green) [46] Cao 等 [47] [47] Fig. 18 Instantaneous contours of (a) heat release rate, and (b) vorticity in different combustion regions [47] 2.2 凹腔几何形状 [48] Fig. 19 Pathlines from the fuel injector colored with residence time (in milliseconds) for the baseline (left), square cavity (center), and inclined cavity (right) configurations [48] Zhao 等 [50] 通过实验发现凹腔及其下游是最 敏感的区域：较高的凹腔长深比、较陡的凹腔后 壁倾斜角、凹腔下游更近的空气节流会导致凹腔 剪切层的抬升，从而引发燃烧振荡，Ruan 等 [51] 的研究也发现了凹腔内回流区的特征与凹腔的长 深比有直接关系。Mahto 等 [52] 提出燃烧室存在一 个最佳长深比 L/D=7，可以显著提高燃烧室的性 能，实现高效燃烧。Zhang 等 [ [39] 并联凹腔方面，Choubey 和 Pandey 等 [58,59] [66] Fig. 23 Comparison of H2 mass fractions on jet planes of different injection methods [66] Fig. 25 Cavity configurations used to tailor the mean pressure gradient [72] 空气节流已被实验证实是一种增强高速超燃 冲压发动机燃料射流点火的有效技术，近年来也 被一些研究所采用。Yuan 等 [73] 在不同凹腔燃料 喷注方式的基础上添加空气节流，数值研究评估 了空气节流策略对氢燃料凹腔燃烧室性能的影 响。结果表明，空气节流可以通过增加背压、燃 料停留时间和混合气均匀性来改善点火环境。 传统的凹腔点火方式为火花塞放电点火，这 种点火方式是被动的，点火核和火焰沿着凹腔流 场传播，可靠性较差。近年来随着等离子点火技 术的发展，涌现出诸多新型点火技术例如激光诱 导等离子体点火 [74] 、双频激励等离子体(Dualfrequency excited plasma, DFEP)点火 [75] 、脉冲爆 震(Pulse detonator, PD)点火 [76] 、长电极距离高 能 火 花 点 火 器 ( Long electrode distance highenergy spark igniter, LHSI) [ section of a horizontal strut [88] 图 27 竖直支板流向截面速度场与压力场 [88] Fig. 27 Velocity and pressure fields in the flow direction section of a vertical strut [88] [89] Yu 等 [ rectangle shaped injector [102] 航 空 学 报 ...

Reference:

Research progress on mixing and combustion performance of strut/cavity- based combustor 支板/凹腔燃烧室混合与燃烧性能研究进展

... The flame acceleration (FA) and the subsequent deflagrataion-to-detonation Transition (DDT) processes have been extensively studied over the decades via both experiments 24,26 and computation [2][3][4]9,11 . The topic holds tremendous significance from both a fundamental standpoint (as a connecting link between deflagrative and detonative combustion modes) and also a practical perspective, with regards to industrial safety and detonation engine startup where detonation initiation is achieved via DDT. ...

Reference:

Flame acceleration and deflagration to detonation transition in a microchannel with catalytic nickel walls