Blade/casing rubbing interactions in aircraft engines: Numerical benchmark and design guidelines based on NASA rotor 37

Abstract

Blade/casing rubbing interactions in aircraft engines: Numerical benchmark and design guidelines based on NASA rotor 37. Journal of Sound and Vibration, Elsevier, 2019, 460, pp.Abstract In order to improve the efficiency of aircraft engines, the reduction of clearances between blade tips and their surrounding casing is one avenue manufacturers consider to lower aerodynamic losses. This reduction increases the risk of blade tip/casing contact interactions under nominal operating conditions. Designers need tools to accurately predict subsequent nonlinear vibrations. Engineers and researchers have developed a variety of sophisticated numerical models to predict blades' responses. These models are related to distinct frameworks (time/frequency domain) and various solution algorithms (explicit/implicit time integration schemes, penalty/Lagrange multiplier contact treatment...) which calls for comparative analyses. However, published results are often limited for the sake of confidentiality thus preventing any detailed confrontation. While qualitative understanding can be gained from simplified academic models, full scale models are needed to predict complex interactions in a realistic manner. In this context, this paper proposes a benchmark featuring detailed simulations and analyses of a full 3D finite element model based on the open NASA rotor 37 compressor blade to facilitate reproducibility and collaboration across the research community. NASA rotor 37, a compressor stage widely used as a test case in aerodynamic simulations and validations, has the advantage of presenting a realistic blade geometry. The geometry of the blade is built from publicly available reports. The paper provides details on the geometry, the numerical model and the results to allow an easy use of this model across the fields of structural dynamics. Two contact scenarios are investigated: one with direct contact against the casing, and one with abradable material deposited on the casing to mitigate contact severity through wear. The nonlinear vibration response of the blade is simulated in the time domain. It is evidenced that the addition of the abradable material decreases the amplitude of vibration for most of the angular speeds investigated. However, new interactions appear for some angular speeds. The obtained results are consistent with previous simulations on industrial geometries. Based on works showing improved aerodynamic performances when the blade is tilted, a total of seven geometries are investigated: the reference blade, with a straight vertical stacking line similar to the original rotor 37, two forward-leaned blades, two backward-swept blades and two full forward chordwise swept blades. The sweep and lean variations are shown to have a dramatic impact on the vibration response: the backward sweep results in an increased blade's robustness to contact events and the full forward chordwise sweep in a reduced robustness, while the forward lean leads to a robustness similar to the reference blade. RésuméLa réduction des jeux au...

Comparative Study of Blades Reduced Order Models With Geometrical Nonlinearities and Contact Interfaces

“…Recently, the idea of using NASA rotor 37 as a benchmark in structural dynamics, and more precisely for contact simulations, has emerged [5]. The establishment of this benchmark comes with a detailed description of the blade, with all necessary geometry parameters and material properties, which is used in this work.…”

“…Regarding the modeling of damping, the assumption of proportional damping is made. As suggested in [5], a modal damping ξ = 5 • 10 −4 is considered for the first bending mode. For the POD reduction method, the reduction basis is composed of 3 constraint modes and (r − 3) POD modes.…”

“…In particular, engine blades are now so slender and flexible that they experience large strains and displacements, yielding geometrically nonlinear behaviors [1,2,3]. At the same time, the need for improved engine efficiency motivates engineers to consider a reduced clearance between the rotating blades and the surrounding casing, which increases the risk of contact occurrences between rotating and stationary components in nominal operating conditions [4,5,6]. Nowadays, the preliminary design of turbomachines in industry in mainly driven by aerodynamic considerations and the absence of contact occurrence is only checked at the end of the process.…”

“…In the field of bladed disk dynamics, recent developments regarding the prediction of contact interactions include the modeling of a flexible casing [25], also with the extension to new materials, such as ceramic matrix composite (CMC) material [6]. The modeling of the removal of an abradable coating on the casing is also addressed in [26,6,5]. However, the classical methods are most of the time limited to small displacements and therefore do not account for geometrical nonlinearities.…”

Nonlinear stochastic dynamics of detuned bladed-disks with uncertain mistuning and detuning optimization using a probabilistic machine learning tool

“…Such local nonlinearities although occur through rotor/stator interaction between the blade tip and the stator casing or when using under-platform dampers yielding blade to blade contact (see e.g. [12,13,14,15,16,17,18]). A research effort has also been made for the construction of nonlinear reduced-order models allowing for the mistuning analysis of bladed-disk in presence of contact nonlinearities [19,20,21,22,23,24,25].…”