Numerical assessment of thermohydraulic performance in pipes with different arrangements of delta winglet pairs via the GEKO turbulence model

This study systematically investigates the effect of varying the number (N) of Delta Winglet Pairs (DWPs) under both constant (CFPA) and non-constant (NCFPA) total frontal projection areas on the thermal–hydraulic performance of tubular heat exchangers. Prior to these investigations, a detailed evaluation of the GEneralized K-Omega (GEKO) turbulence model is performed to ensure its reliability for the present study. The Nusselt number (Nu) and Darcy friction factor (f) of a tubular domain fitted with delta winglet (DW) type vortex generators (VGs) are numerically investigated within Re=5000-25000. The mean absolute deviations of 4.80%, 1.85% and 4.99% are attained with respect to the NuExp., fExp. and TEFExp. respectively. The free parameters are adjusted to C_SEP=1.75 and the corresponding 〖 C〗_MIXCOR (GEKO-1.75). Besides that, the validation of smooth pipe is also carried out and yields an average absolute deviations of 5.42% and 0.85% in comparison to the Dittus-Boelter and Petukhov correlation equations, respectively, with optimized free parameters are set to C_NW=-1.18-2,C_(NW-SUB)=1.7-2.5,C_SEP=1. Based on the analysis carried out within the scope of the NCFPA approach, Thermal Enhancement Factors (TEF) exceeds unity for most cases, with the highest values of 1.28, 1.26, 1.22, and 1.17 at Re=5000 for N=3-6, respectively, indicating the strong contribution of longitudinal vortices at lower Reynolds numbers. In the CFPA approach, although friction increased notably for N=3S, the heat transfer enhancement outweighs the friction penalty, yielding TEF of 1.18 at Re=5000 and ≈1.00 at Re=25000. Overall, the NCFPA approach showed a more pronounced TEF enhancement compared to CFPA, confirming the strong influence of DWP number and arrangement on thermal performance.