Author(s): Ali Abdulnabi Hasan Al-Iessa

Abstract: Variable-conductance conduits and variable-area passages have been widely adopted in aerospace propulsion nozzles, diffusers, thermal exchangers, and conditioning channels, wherein a combined effect of simultaneous variation of area of passage and its thermal conditions dictates the character of convective heat transfer and formation of the local boundary layers. This paper presents results of 3D computational fluid dynamics (CFD) analysis of air flow with turbulence in the form of a hollow truncated conical tube characterized by the inlet diameter D_in = 100 mm, outlet diameter D_out = 50 mm, and axial length L = 500 mm (area ratio 4:1, wall half-angle ? = 2.86°). The conical tube geometry has been considered under the two opposite directions of flow: nozzle-like (converging) configuration and diffuser (diverging) configuration. For each direction of flow, two classical wall thermal boundary conditions are analyzed in the work: constant wall temperature (CWT) and constant wall heat flux (CHF). The throughput is set constant in all the cases, which results in inlet velocity values of 100 m/s (Reynolds number Re ~1.0×105) for nozzle and 400 m/s (Reynolds number Re ~2.0×105) for diffuser. Steady Reynolds-Averaged Navier-Stokes (RANS) equations with realizable k-? turbulence model and enhanced wall function treatment have been solved numerically using the coupled pressure-based finite-volume method. Extensive grid independence analysis was performed to establish the spatial convergence. Under CWT condition, the bulk temperature of the fluid approaches the value of the wall temperature, and the gradient is steep only in the vicinity of the solid wall. Under CHF condition (±30 W/m2), the difference of temperatures becomes much smaller by three orders of magnitude (?10^-2K), because of the significant thermal capacity of the through-flow. The flow reversal leads to the inversion in the direction of heat flow: the conical wall becomes the source of heat in nozzle case (?Tb = +1.18 K, heat Q?+400 W) and the sink of heat in the diffuser case (?Tb = -15.8K, heat Q?-3500 W). Numerical results have been validated against experimental data from variable-area benchmarks, and discrepancies were kept under 1% level.

DOI: https://www.doi.org/10.22271/27078043.2026.v7.i2a.135

Pages: 38-45 | Views: 98 | Downloads: 49

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