Open Rotor Design Strategy: From Wind Tunnel Tests to Full Scale Multi-Disciplinary Design

Abstract

For several years, Safran has been involved in the design and optimization of contra rotating open rotors. This innovative architecture is known for allowing drastic reduction in fuel burn, but its development is facing complex technological challenges such as acoustics, aerodynamics, and weight penalty due to the mechanical complexity of an Open Rotor. Since 2010, Safran has been developing the experimental test bench HERA (1/5 mock-up scale) to improve the understanding of the complex aerodynamics and acoustics phenomena involved in the counter rotating propellers configuration. Isolated and installed low speed and high speed wind tunnel campaigns, including PIV measurements have been extremely helpful in defining design guidelines for full scale open rotor specification. These tests have been used as CFD feed-back among other purposes. An iterative process involving CFD optimization (in close collaboration with Cenaero) and wind tunnel test campaigns has been developed over the last 4 years and has led to the definition of an innovative design strategy, which has been successfully tested during the process of the full scale counter rotating propellers design for the SAGE2 ground test demonstrator engine. This phase has evidenced the absolute necessity of a multi-disciplinary design method when it comes to full scale and “rig-ready” design. Ensuring high propulsive efficiency and at the same time, minimizing the acoustic level, while maintaining severe mechanical constraints such as weight, inertia and proper dynamic positioning under control, requires a dedicated and integrated “all inclusive” design process. The aim of this paper is to present the design methodology and some of the wind tunnel tests results carried out over the last 4 years, which have led to the definition of a novel multidisciplinary design methodology that involves CFD, FEM and acoustics.

Historical development of the coaxial contra-rotating propeller

“…Safran in France has been developing CRP for a number of years, both direct-drive and geared engines. Various levels of multi-disciplinary design and optimisation [122] have produced extremely complex blade geometries that are swept radially and axially; the new blades look like flags in the wind shown in Fig. 4.…”

Rapid Dynamic Load Estimation Procedure for Lifting Propellers in Forward Flight

“…While propeller optimization primarily centers on aerodynamics and aeroacoustics, structural integrity is commonly considered as a constraint [8,9]. However, structural deformations significantly impact aerodynamic performance.…”

“…According to the accident report, the blade disintegration and subsequential crash of Vertical Aerospace's prototype during the 22 nd test flight is most likely due to a degradation of a bonding within the internal blade structure [12]. Unfortunately, some research groups solely implemented static strength requirements in their routines [8,9,13]. Fatigue, frequency response, and aeroelastic instabilities are also mandatory for a vital design [14-16], even though not all of them can be estimated by reduced order methods.…”

On the influence of elasticity on propeller performance: a parametric study

“…Gur and Rosen additionally demonstrated that implementing geometric and structural constraints regarding stress limits within a propeller optimization routine impacts the optimized propeller layout and operating conditions [11]. Modern approaches include structural or aeroelastic constraints in multidisciplinary optimization schemes [12].…”