A modified dual time integration technique for aerodynamic quasi-static and dynamic stall hysteresis

open access articleSimulation of the aerodynamic stall phenomenon in both quasi-static and dynamic conditions requires expensive computational resources. The computations become even more costly for static stall hysteresis using an unsteady solver with very slow variation of angle of attack at low reduced frequencies. In an explicit time-marching solver that satisfies the low Courant number condition, that is, CFL<1, the computational cost for such simulations becomes prohibitive, especially at higher Reynolds numbers due to the presence of thin-stretched cells with large aspect ratio in the boundary layer. In this paper, a segregated solver method such as the Semi-Implicit Method for Pressure-Linked Equations (SIMPLE) is modified as a dual pseudo-time marching method so that the unsteady problem at each time step is reformulated as a steady state problem. The resulting system of equations in the discretized finite volume formulation is then reduced to zero or near-zero residuals using available convergence acceleration methods such as local time stepping, multi-grid acceleration and residual smoothing. The performance and accuracy of the implemented algorithm was tested for three different airfoils at low to moderate Reynolds numbers in both incompressible and compressible flow conditions covering both attached and separated flow regimes. The results obtained are in close agreement with the published experimental and computational results for both quasi-static and dynamic stall and have demonstrated significant savings in computational time

Preservation of Soil Fertility Using Sidereal Clover

This study examined the use of intermediate groundcover sideral crops, such as perennial leguminous herbs, to conserve soil fertility though enriching the soil with fresh organic matter, an effective and low-cost method. Studies show that the use of direct sowing technology allows the preservation of all plant residues on the soil surface, which ensures the best accumulation of snow in the winter. Through the preservation of numerous biodrenes from the root system of sweet clover and other cultivated crops, as well as soil channels from earthworms, this direct sowing technology increases the moisture content of the soil and reduces moisture loss. The effectiveness of various soybean, corn and sunflower cultivation technologies with a minimal tillage period was studied. When sweet clover was used for green manure in April, the maximum yield was obtained, and the maximum yield for corn (57.3-82.3 c/ha) was obtained using the no-till technology. As a consequence, the ground cover crop had a noticeable effect on the yield of the second crop rotation - spring wheat, which had a higher yield. The use of direct sowing technology with sweet clover as green manure provided the highest yield of spring wheat - from 37.2 to 39.8 c / ha. The grain quality of spring wheat, placed as the second crop after melilot on green manure, was higher, both under no-till technology and under mini-till technology. Keywords: biologization, soil fertility, green manure, clover, direct sowing, productivit

Computational Simulation of Airfoils Stall Aerodynamics at Low Reynolds Numbers

Experimental results for aerodynamic static hysteresis at stall conditions obtained in the TsAGI's T-124 low-turbulence wind tunnel for NACA0018 are presented and analysed. Computational predictions of aerodynamic static hysteresis are made using the OpenFOAM simulations considering di erent grids, turbulence models and solvers. Comparisons of compu- tational simulation results with experimental wind tunnel data are made for 2D NACA0018 and NACA0012 airfoils at low Reynolds numbers Re = (0.3-1.0) millions. The properties of the proposed phenomenological bifurca- tion model for simulation of aerodynamic loads at the existence of static hysteresis are discussed

Computational Ground Effect Aerodynamics and Airplane Stability Analysis During Take-off and Landing

Computational simulations of aerodynamic characteristics of the Common Research Model (CRM), representing a typical transport airliner, are conducted using CFD methods in close proximity to the ground. The obtained dependencies on bank angle for aerodynamic forces and moments are further used in stability and controllability analysis of the lateral-directional aircraft motion. Essential changes in the lateral-directional modes in close proximity to the ground have been identified. For example, with approach to the ground, the roll subsidence and spiral eigenvalues are merging creating the oscillatory Roll-Spiral mode with quite significant frequency. This transformation of the lateral-directional dynamics in piloted simulation may affect the aircraft responses to external crosswind, modify handling quality characteristics and improve realism of crosswind landing

Computational Simulation of Airfoils Stall Aerodynamics at Low Reynolds Numbers

Experimental results for aerodynamic static hysteresis at stall conditions obtained in the TsAGI's T-124 low-turbulence wind tunnel for NACA0018 are presented and analysed. Computational predictions of aerodynamic static hysteresis are made using the OpenFOAM simulations considering di erent grids, turbulence models and solvers. Comparisons of compu- tational simulation results with experimental wind tunnel data are made for 2D NACA0018 and NACA0012 airfoils at low Reynolds numbers Re = (0.3-1.0) millions. The properties of the proposed phenomenological bifurca- tion model for simulation of aerodynamic loads at the existence of static hysteresis are discussed

Impact of Ground Effect on Airplane Lateral Directional Stability during Take-Off and Landing

Open Access journalComputational simulations of aerodynamic characteristics of the Common Research Model (CRM), representing a typical transport airliner are conducted using CFD methods in close proximity to the ground. The obtained dependencies on bank angle for aerodynamic forces and moments are further used in stability and controllability analysis of the lateral-directional aircraft motion. Essential changes in the lateral-directional modes in close proximity to the ground have been identified. For example, with approach to the ground, the roll subsidence and spiral eigenvalues are merging creating the oscillatory Roll-Spiral mode with quite significant frequency. This transformation of the lateral-directional dynamics in piloted simulation may affect the aircraft responses to external crosswind, modify handling quality characteristics and improve realism of crosswind landing. The material of this paper was presented at the Seventh European Conference for Aeronautics and Space Sciences EUCASS-2017. Further work is carried out for evaluation of the ground effect aerodynamics for a high-lift configuration based on a hybrid geometry of DLR F11 and NASA GTM models with fully deployed flaps and slats. Some aspects of grid generation for a high lift configuration using structured blocking approach are discussed

Prediction Of Static Aerodynamic Hysteresis On A Thin Airfoil Using OpenFOAM

The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link.The paper presents computational prediction of aerodynamic hysteresis loops in static conditions for a two-dimensional aerofoil that was used as a cross-section profile for a rectangular wing with an aspect ratio of five, tested in the TsAGI T-106 wind tunnel at a Reynolds number of =6×106 and a Mach number of =0.15. Tests in the wind tunnel showed that minor changes in the curvature of the leading edge of the thin aerodynamic profile lead to a significant increase in the maximum lift coefficient when significant hysteresis loops appear in the aerodynamic characteristics of the wing. The computational predictions of stall aerodynamics presented in this paper are made for a two-dimensional profile using the OpenFOAM open-source code to simulate a flow based on the unsteady Reynolds-averaged Navier–Stokes equations using the Spalart–Allmaras turbulence model. The calculation results confirm the existence of loops of static aerodynamic hysteresis and bistable structures of the separated flow, and the results are qualitatively similar to the results observed experimentally on the wing with a finite aspect ratio

Aerodynamic Modeling for Post-Stall Flight Simulation of a Transport Airplane

The file attached to this record is the author's final peer reviewed version.open access articleThe principles of aerodynamic modeling in the extended flight envelope, which is characterized by the development of separated flow, are outlined and illustrated for a generic transport airplane. The importance of different test techniques for generating wind tunnel data and the procedure for blending the obtained experimental data for aerodynamic modeling are discussed. Complementary use of computational fluid dynamics simulations reveals a substantial effect of the Reynolds number on the intensity of aerodynamic autorotation, which is later reflected in the aerodynamic model. Validation criteria for an extended envelope aerodynamic model are discussed, and the important role of professional test pilots with post-stall flying experience in tuning aerodynamic model parameters is emphasized. The paper presents an approach to aerodynamic modeling that was implemented in the project Simulation of Upset Recovery inAviation (2009–2012), funded by the EuropeanUnion under the seventh framework programme. The developed post-stall aerodynamic model of a generic airliner configuration for a wide range of angles of attack, sideslip, and angular rate was successfully validated by a number of professional test pilots on hexapod and centrifuge-based flight simulator platforms