Computational modeling of complex supersonic airflow patterns is one of the greatest challenges in the domain of CFD analyses. The paper presents initial steps in numerical analysis of such flow, generated by convergentdivergent nozzle with Mach number M = 2.6 at nozzle exit. The aim was to achieve good agreements with available experimental data, obtained during supersonic wind tunnel tests at VTI Žarkovo institute, where nozzle thrust vectoring possibilities had been investigated using air as test fluid, by placing different types of obstacles at the exit section. Paper is focussed on free exit flow, and flow with one selected obstacle type. Using structured mesh for both cases, the RANS equations with k-w SST turbulent model have been applied. After quantitative and qualitative comparisons with available experimental data, good agreements have been obtained, where CFD was also able to provide additional flowfield data, not measuted during experiments.

During the evolution of an airplane aerodynamic design, proper calculation methods and software tools should be utilized, which correspond to the airplane category and project development level. In case of light aircraft, the general trend is the application of analytical and semiempirical methods at the initial stages, combined with simplified - inviscid CFD computational models, and fairly complex viscous CFD analyses at higher design levels. At the present stage of light aviation development, it is assumed that the contemporary design tools for each of those steps should be appropriate enough, so that they actually verify and additionally fine-tune each other's results. This paper describes the calculation tools and methods applied during the aerodynamic analyses of a new light aircraft at different development stages, and compares the results obtained by them, with the aim to verify and support the above statement, considering light aircraft aerodynamic design.

U okviru ove studije, ustanovljen je CFD (Computational Fluid Dynamics) proračunski model za potrebe analize kompleksnog nadzvučnog strujnog polja generiranog 2D konvergentno-divergentnim mlaznikom. U cilju simulacije upravljanja...

This paper presents the second stage of a tandem fixed-wing unmanned aerial vehicle (UAV) aerodynamic development. In the initial stage, the UAV was optimized by analyzing its characteristics only in symmetrical flight conditions. Posted requirements were that both wings should produce relevant positive lift, the initial stall must occur on the front wing first, the center of pressure should be close to the center of gravity, and longitudinal static stability should be in the optimum range. Computational fluid dynamic (CFD) analyses were performed, where the applied calculation model was derived from the authors’ previous successful projects. The eighth version TW V8 has satisfied all longitudinal requirements. Lateral-directional CFD analyses of V8 showed that the ratio of the lateral and directional stability at the nominal cruising regime was optimal, but both lateral and directional static stabilities were too high. On further development versions, the lower vertical tail was eliminated, a negative dihedral was implemented on the front wing, and four inverted blended winglets were added. Version TW V14 has largely improved lateral and directional stability characteristics, while their optimum ratio at the cruising regime was preserved. Longitudinal characteristics were also well preserved. Maximum lift coefficient and lift-to-drag ratio were increased, compared to the V8.

Purpose: Unmanned aerial vehicles (UAV) with remote and/or automated flight and mission controls have replaced airplanes with pilots in many important roles. This study aims to deal with computational fluid dynamics (CFD) analysis and development of the aerodynamic configuration of a multi-purpose UAV for low and medium altitudes. The main aerodynamic requirement was the application of the tandem wing (TW) concept, where both wings generate a positive lift and act as primary lifting devices. Design/methodology/approach: Initial design analyses of the UAV’s aerodynamic configuration were performed using ANSYS Fluent. In previous work in Fluent, the authors established a calculation model that has been verified by experiments and, with minor adjustments, could be applied for subsonic, transonic and supersonic flow analyses. Findings: The design evolved through eight development configurations, where the latest V8 satisfied all the posted longitudinal aerodynamic requirements. Both wings generate a substantial amount of positive lift, whereas the initial stall occurs first on the front wing, generating a natural nose-down stall recovery tendency. In the cruising flight regime, this configuration has the desired range of longitudinal static stability and its centre of pressure is in close proximity to the centre of gravity. Practical implications: The intermediate development version V8 with proper longitudinal aerodynamic characteristics presents a good starting point for future development steps that will involve the optimization of lateral-directional aerodynamics. Originality/value: Using contemporary CFD tools, a novel and original TW aerodynamic configuration have evolved within eight development stages, not being based on or derived from any existing designs.

Iosif Taposu has formulated a mathematical model and generated a family of airfoils whose geometry resembles the dolphin shape. These airfoils are characterized by a sharp leading edge and experiments have proven that they can achieve better aerodynamic characteristics at very high angles of attack than certain classical airfoils, with the nose geometry inclined downwards. On the other hand, they have not been applied to any commercial general aviation aircraft. The authors of this paper have been motivated to compare the aerodynamic characteristics of widely used NACA 2415 airfoil with Taposu?s Dolphin that would have the same principal geometric characteristics. A CFD calculation model has been established and applied on NACA 2415. The results were compared with NACA experiments and very good agreements have been achieved in the major domains of lift and polar curves. The same CFD model has been applied on the counterpart Dolphin 2415. Results have shown that the Dolphin has a slightly higher lift/drag ratio in the lift coefficient domain 0.1-0.35 than NACA. On the other hand, at higher and lower lift coefficients, its aerodynamic characteristics were drastically below those of the NACA section, due to the unfavorable influence of the Dolphin?s sharp nose. A series of the Dolphin?s leading edge modifications has been investigated, gradually improving its aerodynamics. Finally, version M4, consisting of about 70% of Dolphin?s original rear domain and 30% of the new nose shape, managed to exceed the NACA?s characteristics, thus paving the way to investigate the Dolphin hybrids that could be suitable for the general aviation industry.