Reduced reliance on wind tunnel data

Transcription

1 Reduced reliance on wind tunnel data The recreation of the industrial gust loads process, using CFD in place of experimental data Investigation of the underlying assumptions of the current industrial gust loads process

2 Updating DLM with CFD simulation data DLM is still no. 1 industrial work horse for gust loads computations Cannot predict effects of wing thickness, (separated) boundary layers, in-plane motion, shocks Usually has to be corrected to match with steady integral wind tunnel or flight test measurements Questions: How does locally corrected DLM behave in comparison to CFD for gust problems? Can we improve the DLM correction with additional unsteady time-linearized CFD input? LANN CT5

3 Steady correct for DLM and UVLM DLM The loads on each DLM strip can be written as F DLM = SA 1 w The difference between the uncorrected DLM and CFD can be written as UVLM The loads on each UVLM strip can be written as F UVLM = SZΓA 1 w This lead to the following equation for the correction factors F = SA 1 wε + C 0 F = SZA 1 wε + SZC 0 This work was carried out by University of Bristol

4 UVLM correction process The corrected UVLM solves the following equations Γ = A(Cw) Where the downwash has two components w = w body + w wake The wake downwash depends on the strength of the shed vortex panels/particles. So the wake downwash changes with the correction matrices so the correction procedure has to be iterated This work was carried out by University of Bristol

5 UAV gust response rigid 30ft 150ft 350ft This work was carried out by University of Bristol

6 UAV gust response aeroelastic 30ft 150ft 350ft This work was carried out by University of Bristol

7 Rigid Aeroelastic Funded by the NCRM gust response 30ft 150ft 350ft This work was carried out by University of Bristol

8 CFD results NCRM free-free rigid case H This work was carried out by University of Bristol

9 AIC Unsteady Correction Rigid Gust Funded by the The aim of this correction approach is to match the integrated aerodynamic loads acting on the structural nodes computed from the CFD code: where the right hand side term can be specialized for the corrected Doublet Lattice Method, as follow: A post multiplication correction approach The downwash contribution is a matrix defined as follow Defining the generalized aerodynamic influence coefficient matrix relating the downwash to the aerodynamic loads on the monitor points, corresponding to the CFD strip being mentioned: This work was carried out by University of Bristol

10 AIC Unsteady Correction Framework The time domain CFD gust response loads have been evaluated for different reduced frequencies. Funded by the For each of them the time history of the integrated loads of the ten strips along the wing has been computed. The input signal has been chosen long enough to reach a stationary harmonic response. At this point a reference period has been selected, and an equivalent periodic signal has been reconstructed. To obtain comparable results to the ones computed by the DLM the Fourier Series has been used to obtain the frequency domain loads. The correction factors have been used to update the AICs matrices computed in the gust response analysis. This work was carried out by University of Bristol

11 1-COS Gust Response Analysis The main goal is to focus on the gust response analysis of interest in a design process: short medium large With a design gust velocity given by : Mach number = This work was carried out by University of Bristol

12 This work was carried out by University of Bristol Funded by the

13 Updating DLM with CFD simulation data Neither time-linearized CFD nor perfectly corrected DLM will ever be able to reproduce dynamic nonlinearity Nevertheless: Perfect match for small perturbations is seen as a necessary ingredient for a multi-purpose ROM in the first place This work was carried out by DLR

14 Updating DLM with CFD simulation data Test case: Clean wing geometry (Aerostabil) at transonic conditions Quasi-steady correction only (CREAM) Even oscillatory nature of separated flow can be captured α=0 α=8 This work was carried out by DLR

15 Updating DLM with CFD simulation data Test case: NASA CRM Quasi-steady correction only (CREAM) Quality decreases for higher frequencies / shorter gusts Long gust Short gust This work was carried out by DLR

16 Updating DLM with CFD simulation data Test case: Clean wing geometry (Aerostabil) at transonic conditions Unsteady correction with 1 unsteady CFD input (CREAM-1) This work was carried out by DLR

17 Updating DLM with CFD simulation data Test case: 3-DOF NASA CRM incl. fluid-structure coupling Huge qualitative discrepancies! AIC corrections may result in erratic GAFs at higher frequencies and unreasonable aircraft dynamics Needs further investigation! Forces Motion heave pitch bend This work was carried out by DLR

18 Summary Corrections for DLM/UVLM using steady state data compared to CFD for rigid and flexible clamped configurations Rigid body simulations of NCRM, free in heave and pitch show that the NCRM enters a steady state climb after encountering larger gusts Unsteady CFD-based has the potential to improve DLM corrections used in the gust loads process

19 The research leading to this work has received funding from the s Horizon 2020 research and innovation programme under grant agreement number