Brown, N. (2019) Highfidelity computational fluid dynamics methods for the simulation of propeller stall flutter. A time-marching aeroelastic method developed for the study of propeller flutter is presented and validated. Propeller flutter can take many forms with stall, whirl and classical flutter being the primary responses. These types of flutter require accurate capture of the non-linear aerodynamics associated with propeller blades. Stall flutter in particular needs detailed unsteady flow modelling. With the development of modern propeller designs potentially adjusting the flutter boundary and the development of faster computing power, CFD is required to ensure accurate capture of aerodynamics. Given the lack of reliable experimental stall flutter data for propellers, the method was focused on observing the correct qualitative behaviour with a comparison made between URANS and Scale-Adaptive Simulation (SAS). Greek α s m = Model amplitude of mode m of solid s (m/kg) ζ m = Damping coefficient (-) ρ = Fluid density (kg/m 3 ) ψ s m = Normalised m th mode displacement of solid s (m/kg) ψ s = Normalised displacement of solid s (m/kg) ω m = Natural frequency of mode m Ω CV = Control volume size Subscripts i, j, k = Mesh cell indices
Aeroelastic phenomena of stall flutter are the result of the negative aerodynamic damping associated with separated flow. From this basis, an investigation has been conducted to estimate the aerodynamic damping from a time-marching aeroelastic computation. An initial investigation is conducted on the NACA 0012 aerofoil section, before transition to 3D propellers and full aeroelastic calculations. Estimates of aerodynamic damping are presented, with a comparison made between URANS and SAS. Use of a suitable turbulence closure to allow for shedding of flow structures during stall is seen as critical in predicting negative damping estimations. From this investigation, it has been found that the SAS method is able to capture this for both the aerofoil and 3D test cases.
A time-marching aeroelastic method developed for the study of propeller flutter is presented and validated. Propeller flutter can take many forms with stall, whirl and classical flutter being the primary responses. These types of flutter require accurate capture of the non-linear aerodynamics associated with propeller blades. Stall flutter in particular, due to the highly detached nature of the flow, needs detailed unsteady flow modelling. With the development of modern propeller designs potentially adjusting the flutter boundary and the development of faster computing power, CFD is required to ensure accurate capture of aerodynamics. This paper focuses on the validation of the aeroelastic method using the Commander propeller blade.
Induction bending offers a rapid, cost-effective method of producing complex convoluted pipework. The resultant bends, however, typically show unwanted geometric deformations which include wall thinning at the extrados, wall thickening at the intrados, awkward transitions on going from tangent to bend, and wrinkling at the intrados surface. All forms of geometric deformation are worse depending on the tightness of the bend and the thickness of the original pipe. Predicting the final geometry of the bend is a non-trivial problem.This article first considers the use of simple analytical models to predict the final deformed geometry of induction bends in thick-walled pipe. It then goes on to compare the predicted geometry obtained from those analytical models with the outputs from empirically derived charts and computational models. The article concludes that empirically derived charts do not offer accurate predictions of wall thinning, are not currently available for intrados wall thickening, and cannot, with confidence, be extrapolated to produce accurate results for very tight bends. Numerical models are developed which predict wall thickening and thinning for any combination of outside diameter/wall thickness/bend radius combination; however, it is concluded that their limited accuracy makes their use questionable. Elastic-plastic FEA is developed which is shown to provide the most consistently accurate means of predicting both wall thickening and wall thinning, and, while not providing a comprehensive prediction of the post-bend geometry did, nevertheless, to go some way towards predicting the overall deformed geometry including transition ramps and intrados surface wrinkling.
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