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Regeneratively cooled scramjet heat transfer calculation method was developed using three-dimensional calculation for engine solid wall heat conduction. The scramjet thermal environment was determined by engine heat flux measurement and the engine three-dimensional combustion flow calculations. Different heat transfer relationships in the laminar, transition and turbulence fuel flow regions were applied. The cooling fuel flow distribution data inside combustion chamber side panel were obtained by three-dimensional fuel cooling flow calculation. The results of a light weight regeneratively cooled combustion chamber heat transfer tests were adopted to verify the calculation method. The comparisons showed good agreement, indicating that the calculation method is applicable.

Coolant flow and thermal cracking process play key roles in regenerative cooling of a hydrocarbon-fueled scramjet. In order to study the heat transfer and thermal cracking process of regenerative cooling structure, a three dimensional numerical method is established. The Modified Kumar-Kunzru chemical kinetics model consisting of primary reaction and secondary reactions is used to simulate the thermal cracking process. The SIMPLE algorithm is applied to solve the low speed flow field. The data of electrically heated tube tests and a fuel-cooled panel test are adopted to validate the numerical method and chemical model. The comparisons show good agreements between calculated results and test data. The study indicates that the numerical method is an effective tool to investigate the heat transfer and thermal cracking process of regenerative cooling structure for scramjet, and a potential tool to solve the flow design problem. NomenclatureA = flowing area of the tube cross section c p = fluid specific heat capacity at constant pressure d i = the inner diameter of the tube d o = the outer diameter of the tube D k = dissipation term of turbulent kinetic energy k D s = diffusion coefficient of species s h t = total enthalpy (includes the kinetic energy) per unit mass I = the electric current passing through the tube k = turbulent kinetic energy k s = the thermal conductivity of solid wall Δl = the length of one small segment of tube wall m = fluid mass flux m in = mass flux of inlet kerosene Nu = Nusselt number p = fluid pressure p c = critical pressure P k = production term of turbulent kinetic energy k P loss = the thermal loss rate Pr = Prandtl number q = heat flux R i = the electric resistance of one small segment of tube wall Re = Reynolds number T = temperature 1 Ph.D., 2 T air = room temperature T c = critical temperature T iw = the inner wall temperature T f = fluid mean temperature T ow = the outer wall temperature u = fluid velocity x = the Cartesian coordinate Y s = mass fraction of species s= the Kronecker delta λ = thermal conductivity of the fluid μ = fluid viscosity ρ = fluid mean density τ ij = viscous stress tensor ω = specific dissipation rate subscripts i = ith axis in the Cartesian coordinate, species i j = jth axis in the Cartesian coordinate k = quantity related with turbulent kinetic energy k l = laminar s = species s t = turbulent tr = transition ω = quantity related with specific dissipation rate ω

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Nageia nagi (Thunb.) Kuntze is widely cultivated in China for its ornamental and economic value. In August 2019, a leaf spot was observed on N. nagi plants at the campus of Jiangxi Agricultural University (28°45′56″N, 115°50′21″E). Disease incidence was about 35%, and the diseased leaf rate was above 40%. The early symptoms were small spots on the edge or tip of the leaves. The spots gradually expanded and became reddish-brown, eventually developing large irregular lesions. Leaf pieces (5 × 5 mm) from the lesion borders were surfaced sterilized in 70% ethanol for 30 s, followed by 2% NaOCl for 1 min, and then rinsed three times with sterile water. Tissues were placed on potato dextrose agar (PDA) and incubated at 25°C (Zhang et al. 2021). Pure cultures were obtained by transferring hyphal tips to new PDA plates. Twenty-six isolates of Colletotrichum ssp. were obtained (isolation frequency about 82%). Three representative single-spore isolates (ZB-1, ZB-3, and ZB-7) were used for morphological studies and phylogenetic analyses. Colonies on PDA medium of the three isolates were white to gray in color with cottony mycelia. Conidia were single-celled, straight, hyaline, cylindrical, clavate, and measured 14.1-17.9 ×4.4-6.8 µm (15.6 ± 1.2 × 5.4 ± 0.3 µm, n = 100). Appressoria were brown to dark brown, ovoid to clavate, slightly irregular to irregular, and ranged from 5.7-9.3 × 4.6-6.9 µm (7.8 ± 0.2 × 5.6 ± 0.3 µm, n=100). Morphological features were similar to Colletotrichum siamense complex (Weir et al. 2012). The internal transcribed spacer (ITS) regions, actin (ACT), calmodulin (CAL), β-tubulin 2 (TUB2), chitin synthase (CHS-1), and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) were amplified from genomic DNA for the three isolates using primers ITS1/ITS4, ACT-512F/ACT-783R, CL1/CL2, T1/Bt2b, CHS-79F/CHS-354R and GDF/GDR (Weir et al. 2012), respectively. Sequences of them deposited in GenBank under nos. OL826760 - OL826762 (ITS), OL830205 - OL830207 (ACT), OL830196 - OL830198 (GAPDH), OL830193 - OL830195 (TUB2), OL830199 - OL830201 (CHS-1), and OL830202 - OL830204 (CAL). A Blast search of GenBank showed that ITS, ACT, GAPDH, TUB2, CHS-1, and CAL sequences of the three isolates were identical to Colletotrichum siamense at a high level (Table 1). A maximum likelihood and Bayesian posterior probability analyses using IQtree v. 1.6.8 and Mr. Bayes v. 3.2.6 with the concatenated sequences placed ZB-1, ZB-3, and ZB-7 in the clade of C. siamense. Based on the multi-locus phylogeny and morphology, three isolates were identified as C. siamense. The pathogenicity of three isolates was tested on six N. nagi plants (three for inoculation, three for controls), which were grown in the field. Six healthy leaves were wounded with a sterile needle and inoculated with 10 µL of conidial suspension (1 × 106 conidia/mL) per plant. Healthy leaves were inoculated with ddH2O as a control by the same method. All the inoculated leaves were covered with plastic bags to keep a high-humidity environment for 2 days. The experiment was repeated three times. All the inoculated leaves showed similar symptoms to those observed in the field, whereas control leaves were asymptomatic for 8 days. C. siamense was reisolated from the lesions, whereas no fungus was isolated from control leaves. Up to now, Cephleuros virescens, Pestalotiopsis longisetula, Alternaria tenuissima, A. alternate, and Phoma glomerata could infect N. nagi (Zhou et al. 2015; Zhang et al. 2016), and cause leaf spots in China. To our knowledge, this is the first report of C. siamense causing leaf spots on N. nagi worldwide. This work provided crucial information for epidemiologic studies and appropriate control strategies for this newly emerging disease.