Airfoil Performance of Small-Scale Vertical Axis Wind Turbines Under Urban Low Wind Speeds Using DMST and LLFVW Models

This work presents a comparative analysis of six airfoil profiles for small-scale vertical axis wind turbines (VAWTs) operating under low wind speeds (2–8 m/s) typical of urban environments. Aerodynamic performance during startup and nominal operation is investigated using two widely adopted modeling approaches, the Double Multiple Streamtube (DMST) and the Lifting Line Free Vortex Wake (LLFVW) methods, implemented in the open-source QBlade framework. The objective of the study is to evaluate relative airfoil performance and the consistency of observed trends across aerodynamic models commonly used in early-stage VAWT design. The results demonstrate a fundamental trade-off between self-starting capability at low tip-speed ratios (λ<2) and power efficiency at nominal operating conditions (2≤λ≤4). Low-Reynolds-number and VAWT-oriented airfoils (S1210, E387, and DU 06-W-200) show enhanced startup torque under weak inflow conditions, whereas symmetric NACA airfoils (NACA 0015 and NACA 0018) deliver higher power coefficients once operational tip-speed ratios are achieved. Comparison with experimental benchmark data indicates that the transient LLFVW model yields improved agreement relative to the stationary DMST approach, which tends to overestimate performance at moderate and high tip-speed ratios. Overall, the study provides practical guidance for airfoil selection in micro-scale VAWTs intended for urban applications, where reliable self-starting and efficient operation must be carefully balanced.