Oct

10

Cleared for landing

Numerical methods for the definition of the hinge moments of the nose landing gear doors of the commercial aircraft

The conclusions presented in this white paper show strong agreement with the experimental data and demonstrate the ability to use these software solutions to calculate the loads on the landing gear doors during the design stages.

Olga Viktorovna Pavlenko

TsAGI

A.V. Makhankov and Andrey Chuban

Irkut Corporation

The results of the numerical study of aerodynamic loads on the nose landing gear doors demonstrated in this white paper were obtained in Ansys® Fluent and Siemens Digital Industries Software’s Simcenter™ FLOEFD™ software, based on the solution of the Reynolds averaged and Favre averaged Navier-Stokes equations, accordingly.
Computational fluid dynamics (CFD) methods based on the numerical calculation of hydrodynamic equations are widely used to investigate the impact of fluid flow on an aircraft’s units, in addition to conventional analytical approaches and experimental tests. Improved CFD methods can serve as a good alternative to routine experiments in solving practical problems.

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The aerodynamic load data obtained from CFD analysis allows engineers to estimate the doors’ strength, define the opening actuator’s characteristics, and run the optimization of the kinematic connection between small rear doors with the landing gear strut. For the considered aircraft, the initial variant of the small landing gear door rod mounting to the landing gear main fitting has been replaced by the mounting to the landing gear strut to reduce the loads on the rod. The calculation results obtained for the selected variant of the doors were confirmed experimentally, validating the modern software’s results.

The results of the numerical study of aerodynamic loads on the nose landing gear doors demonstrated in this white paper were obtained in Ansys® Fluent and Siemens Digital Industries Software’s Simcenter™ FLOEFD™ software, based on the solution of the Reynolds averaged and Favre averaged Navier-Stokes equations, accordingly.

The numerical study in Simcenter FLOEFD software was performed using rectangular computational mesh adapted to the surface (about 2.5 million cells). To accelerate the calculations the local meshes with the increased mesh resolution around the nose of the fuselage and landing gear doors were used. The automatically adapting computational mesh with concentration in the areas of high gradients of velocity was applied.

Simcenter FLOEFD uses a relatively small number of cells of the computational mesh. In case of a low resolution boundary layer, the approach based on the Prandtl boundary layer hypothesis is applied.

The turbulence model used in Simcenter FLOEFD is based on the modified model with damping functions proposed by Lam and Bremhorstom

Flow around the opening of the large nose landing gear doors

The calculations and experimental investigations show that in the closed position (δdoor1 = 0°, δdoor2 = 0°, δstrut = 0°) hinge moments of the nose landing gear doors are minimal (figure 1).

This is due to gaps along the doors which balance the static pressure on the outer surfaces near their edges and in the landing gear niche.

A calculation of the loads without considering these gaps leads to an overestimation of normal forces acting on the detachment of the doors because the aircraft’s nose gear is in the flow acceleration zone from the nose of the fuselage to the regular part. Since at the sideslip angle of 5° nature of the flow around the fuselage nose does not significantly change, the hinge moments of the closed doors are independent on the sideslip angle within a specified range.

                                                       Fluent

Flow around the small landing gear doors during the release of the nose landing gear

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