high fidelity gust simulations over a supercritical airfoil · • the span-wise extend has been...

Funded by the European Union

AMERICAN INSTITUTE OF AERONAUTICS AND ASTRONAUTICS

High fidelity gust simulations over a supercritical airfoil

B. Tartinville1, V. Barbieux2, L. Temmerman1

1Numeca International, 2 Numflo

AVIATION, 25–29 June 2018

Hyatt Regency Atlanta, Atlanta, Georgia



Outline of the presentation

1Objectives

and Methodology

2Gusts

simulations

3Analysis of the

flow solution

4Conclusions and

Perspectives



The major objectives of the AeroGust project are:

• To carry investigations using CFD so that the non-linearities in gust interactions are

understood.

• To create a gust load process that does not require wind tunnel data and hence reduces

the need for wind tunnel testing.

• To develop updated reduced order models for gust prediction that account for non-linearity

at an acceptable cost.

The objective of this work is to investigate aerodynamic non-linearities due to gust-aircraft

interactions by using high fidelity LES/DES methods for gust simulations.

Objectives and Methodology



High fidelity modelling of gust-airframe interaction

Only a few papers are dealing with high fidelity modelling to investigate gust-airframe

interaction. Those are mainly coming from DLR, Air Force Research Laboratory, and

University of Maryland.

Vorticity contours at different time demonstrating the effect of sharp-edge gust on a SD7703 airfoil at 4° angle of incidence from Golubev et al. [2010] ILES.

Gu

st f

ron

t

Gu

st r

ear

t=16.6 t=16.8 t=26.6 t=26.8 t=32.8




High fidelity modelling of gust-airframe interaction

One of the major challenge for such a high fidelity simulation is to be able to have a correct

gust shape close to the body. To do so, people are commonly using either local source terms,

or mesh refinement convected with the gust.


Example of mesh adaptation for a vortical structure from Tang and Baeder [2007] Example of chimera mesh from Radespiel et al. [2013]



Application of high fidelity gust modelling to FFAST Crank airfoil

• Final test case description has been defined: FFAST crank airfoil with flow condition “I”

• Altitude : 35,000 ft

• Free stream Mach number = 0.86 (U∞ = 255 m/s)

• Chord length : 8 m

• Three gust scenarios

• IDDES model has been retained with a physical time step of 2.10-4 s and an integration

time of several seconds.

• The span-wise extend has been set to half chord (based on best practices for LES/DES).

• A low dissipation scheme has been retained : 2nd order Jameson FV scheme with matrix

dissipation.

• A structured 3D mesh with 16 106 cells has been generated (65 points span-wise) and

mesh convergence has been verified: difference in drag between the two finest grids is

less than one count.




Application of high fidelity gust modelling to FFAST Crank airfoil

High fidelity Hybrid RANS/LES methods have been used by Numeca in the scope of several

EU projects such as ATAAC, DESider, UFAST, TFAST, VAILLANT, and MARS.

Time-mean pressure coefficient PSD for lift coefficient


ComputationExperiment



Gusts are imposed in the far field

• Three gust scenarios are selected H=30 ft, 150 ft, and 350 ft.

• Gusts are imposed via a time-space boundary condition imposing vertical velocity in the

far-field.

Example of time-space evolution of vertical velocity along the far-field boundaries @ x/C=-20




High density mesh for gust convection

• Computational domain extend 20 chords upstream and downstream with a O mesh

topology → domain size 320 m.

• Distribution of mesh points in the far field is sufficiently small to be able to capture the gust

length.

2H = 60 ft

2H = 300 ft

2H = 700 ft




Precursor simulation without gust has been performed

• 90 chord convective time steps (3 s) have been computed with a time step of 5.10-4 s and

a “pseudo periodic” state has been reached.

Animations over the last 0.5 s




Precursor simulation without gust has been performed

At a shock Mach number of about 1.4 a detached flow can be observed downstream.

Almost bi-dimensional fluctuations of the shocks are observed on both sides of the airfoil.

Mid-span Mach number distribution Velocity magnitude distribution [m/s] on iso-surface of l2=-5000





1Objectives

and Methodology

2Gusts

simulations

3Analysis of the

flow solution

4Conclusions and

Perspectives



IDDES for FFAST crank airfoil with shortest gust (H=30 ft)

The passage of the gust has an impact on the shock position – mostly along the suction side.

The shock retrieves its original location after the passage of the gust.

Mid-span Vertical velocity distribution [m/s] Mid-span static pressure distribution [Pa]

Gust simulations



IDDES for FFAST crank airfoil with shortest gust (H=30 ft)

Shock displacement is almost bi-dimensional and impacts the downstream vortical structures

within the wake.

Mid-span Numerical Schlieren Velocity magnitude distribution [m/s] on iso-surface of l2=-5000

Gust simulations



IDDES for FFAST crank airfoil with intermediate gust (H=150 ft)

The passage of the gust has a significant impact on the shock position along both sides. On

the pressure side, the shock almost reaches the airfoil trailing edge.


Gust simulations



IDDES for FFAST crank airfoil with intermediate gust (H=150 ft)

For the most downstream shock position along the pressure side, the detached flow is

drastically reduced.


Gust simulations



IDDES for FFAST crank airfoil with long gust (H=350 ft)

The passage of the gust has a significant impact on the shock position along both sides. On

the pressure side, the shock almost reaches the airfoil trailing edge.


Gust simulations



IDDES for FFAST crank airfoil with long gust (H=350 ft)

For the most downstream shock position along the pressure side, the detached flow is

drastically reduced.


Gust simulations




1Objectives

and Methodology

2Gusts

simulations

3Analysis of the

flow solution

4Conclusions and

Perspectives



Comparison of lift and momentum time evolutions

The two last gust scenarios have a significant impact on the evolution of lift and momentum,

but all the simulations exhibit similar high frequency fluctuations.

Analysis of the flow solution



Frequency content of the lift coefficient

A series of high frequency fluctuations of lift coefficient can be observed at about 35 Hz, 70

Hz, and 90 Hz.


PSD of lift coefficient

St=0

.37

St=0

.29

St=0

.14




High frequency oscillations of lift coefficient are not linked to any high frequency shock

displacement : Kutta waves do not affect the shock location and therefore the lift.

Time evolution of shock location (no gust)Pressure distribution (no gust)





High frequency oscillations of lift coefficient are linked to local variations in surface pressure

within the detached region.

PSD of wall pressure (gust #2)




Analysis of shocks displacements.

Significant shock movements are observed during the passage of the gust.

They have a great impact on the downstream detached region.

Mid-span Numerical Schlieren gust #1 Mid-span Numerical Schlieren gust #2 Mid-span Numerical Schlieren gust #3




Analysis of shocks displacements

Shocks movements exhibits a similar velocity.

Time evolution of shock location

~ 10 m/s




Analysis of shock displacement

Several authors have proposed mechanisms in order to explain self sustained shock

movements.


Model of self sustained shock oscillations from Lee [1990] Wave propagation and interaction with the shock wave from Alshabu and Oliver [2008]



Analysis of shock displacement

The passage of the gust leads to an excess of pressure along the pressure side and a deficit

along the suction side. With such a pressure disturbance of about 7%, Rankine-Hugoniot

equations can explain the observed shock motion.





1Objectives

and Methodology

2Gusts

simulations

3Analysis of the

flow solution

4Conclusions and

Perspectives



A series of high fidelity IDDES gust simulations have been conducted over a

supercritical airfoil.

High frequency lift oscillations are caused by pressure fluctuations within the detached

regions along the surface of the airfoil.

Shock displacement is driven by Rankine-Hugoniot equations and shock velocity is

independent of the gust length.

In order to identify the non-linear impact of shock displacement, one can compare

characteristic times:

It is 0.09, 0.45, and 1.04 for the three gust scenarios.

Conclusions and Perspectives

𝜑 =𝑉𝑠2𝐻

𝑈∞𝑐



The research leading to this work has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement number 636053.

high fidelity gust simulations over a supercritical airfoil · • the span-wise extend has been...

Documents