POLITECNICO DI TORINO I FACULTY OF ENGINEERING

MASTER DEGREE THESIS AEROSPACE ENGINEERING

Study on structural behavior of an atmospheric re-entry vehicle during ditching

Supervisors

• Prof. Giulio Romeo – Politecnico di Torino

• Ing. Roberto Ullio – Thales Alenia Space

Candidate • Maurizio Coltro

The IXV Project

Technology platform

• Intermediate element of technology-effective and cost efficient European roadmap

• Prepare future ambitious operational system developments with limited risks for Europe

Project objectives

• Design, development, manufacturing, on-ground and in-flight verification of autonomous European lifting and controlled re-entry system

Critical technologies of interest

• Advanced instrumentation for aerodynamics and aerothermodynamics

• Thermal protection and hot-structures solutions

• Guidance, navigation and flight control

Success of IXV mission

• Correct performance of re-entry

• Safe landing and recovery with its experimental data 1/17

Experimental measurements

Mockup

• representative of external shape • inertial properties • scale factors

Physical quantities

• accelerations • pressures

Test facility

• electromagnets to release vehicle • high frequency cameras • high pool dimension to perform impact

2/17

Modeling methodology

• Hypermesh • Hypercrash

Preprocessor

• Radioss BLOCK V10

Solver • Hyperview

Postprocessor

Explicit solution tecnique

Drawbacks

• conditional stability

∆𝑡 ≤𝑙𝑐

𝐶

• smallest element determines timestep

Suited for problems

• short duration • high velocity • highly nonlinear

nature

3/17

IXV numerical model

STRUCTURE CONFIGURATION

Fuselage components

Flaps assembly

MODELING ASSUMPTIONS

External dimensions taken into account

Bidimensional rapresentation of surfaces

Rigid body description

RIGID BODY INERTIAL PROPERTIES

Mass Jxx Jyy Jzz

[kg] [𝑘𝑔 𝑚2] [𝑘𝑔 𝑚2] [𝑘𝑔 𝑚2]

27,82 1,17 4,52 4,31

4/17

Fluid numerical model

FLUID DESCRIPTION

LAW37 Biphas

ALE approach

MODELING ASSUMPTIONS

Gas volume extension

Liquid volume extension

5/17

Fluid numerical model

HORIZONTAL EXTENSION

• Limited front dimensions to avoid wave reflection

VERTICAL EXTENSION

• Limited in-deep dimensions to lighten fluid model

WATER BASIN COMPARISON

Deep water model Shallow water model

Horizontal 1,22 x 2,14 [m] 1,22 x 2,14 [m]

Vertical 0,8 [m] 0,4 [m]

N Elements 335265 189317

CPU Time 8413 [s] 5077 [s]

0 0,02 0,04 0,06 0,08 0,1 0,12 0,14 0,16 0,18

Time [s]

Z Acceleration - Accelerometer T1064-63 (COG)

Shallow Water Model Deep Water Model

6/17

Characteristic elements dimension

OPTIMAL 𝒍𝟐𝑫

𝒍𝟑𝑫 RATIO

Finest mesh normal to

phenomenon

Sensitivity analysis

2D ELEMENTS (VEHICLE)

3D ELEMENTS (AIR)

3D ELEMENTS (WATER)

HEIGHT 20 [mm] 20 [mm] 20 [mm]

WIDTH 20 [mm] 20 [mm] 20 [mm]

DEPTH / 10 [mm] 10 [mm]

N ELEMENTS 3564 78324 287188

7/17

Fluid-structure interface

SENSITIVITY ANALYSIS

PERFORMED

NOMINAL PARAMETER

VALUES

• 𝐆𝐚𝐩 = 1.5 Lc

• 𝐒𝐭𝐟𝐚𝐜 =ρ V2 Sel

Gap

FLUID STRUCTURE INTERFACE

TYPE18

STFAC

Interface stiffness

GAP

Activation distance

• Single TYPE18 interface to represent sensors separately

PRESSURE PROBES INTERFACE

8/17

Boundary-initial conditions

• Atmospheric pressure to water free surface • DYREL dynamic relaxation for convergence

• Gravity load to water volume • Lateral/bottom surfaces locked • FLRD = 1 upper surface

WATER BOUNDARY

CONDITIONS

• Initially locked in all DOFs • Gravity load to master node • Initial velocity to master node • Initial distance from free surface

VEHICLE BOUNDARY

CONDITIONS

9/17

Numerical - Experimental Correlation

• Impact angle 35 deg • Flaps position 0 deg • Vertical velocity 3,4 m/s

FIRST

LOADCASE

• Impact angle 19 deg • Flaps position 0 deg • Vertical velocity 3,4 m/s

SECOND

LOADCASE

• Impact angle 51 deg • Flaps position 21 deg • Vertical velocity 3,4 m/s

THIRD

LOADCASE

• Impact angle 35 deg • Flaps position 21 deg • Vertical velocity 3,4 m/s

FOURTH

LOADCASE

All loadcases computed from 0 to 200 ms

10/17

First Loadcase A

X -

CO

G

AZ

- C

OG

-0,2

0

0,2

0,4

0,6

0 0,02 0,04 0,06 0,08 0,1 0,12 0,14 0,16 0,18

t [s]

-0,5

-0,4

-0,3

-0,2

-0,1

0

0,1

0,2

0 0,02 0,04 0,06 0,08 0,1 0,12 0,14 0,16 0,18

t [s]

Numerical

Experimental

11/17

Second Loadcase

-0,4

-0,3

-0,2

-0,1

0

0,1

0 0,02 0,04 0,06 0,08 0,1 0,12 0,14 0,16 0,18

t [s]

-0,4

-0,2

0

0,2

0,4

0,6

0,8

0 0,02 0,04 0,06 0,08 0,1 0,12 0,14 0,16 0,18

t [s]

AX

- C

OG

A

Z -

CO

G

Numerical

Experimental

12/17

Third Loadcase

-0,4

-0,3

-0,2

-0,1

0

0,1

0,2

0,3

0 0,02 0,04 0,06 0,08 0,1 0,12 0,14 0,16 0,18

t [s]

-0,2

-0,1

0

0,1

0,2

0,3

0,4

0 0,02 0,04 0,06 0,08 0,1 0,12 0,14 0,16 0,18

t [s]

AX

- C

OG

A

Z -

CO

G

Numerical

Experimental

13/17

Third Loadcase

-0,10

0,00

0,10

0,20

0,30

0,40

0 0,02 0,04 0,06 0,08 0,1 0,12 0,14 0,16 0,18 0,2

t [s] 19

de

g S

en

so

r

-0,20

0,00

0,20

0,40

0,60

0,80

0 0,02 0,04 0,06 0,08 0,1 0,12 0,14 0,16 0,18 0,2

t [s]

-0,20

0,00

0,20

0,40

0,60

0,80

1,00

0 0,02 0,04 0,06 0,08 0,1 0,12 0,14 0,16 0,18 0,2

t [s]

35

de

g S

en

so

r

51 d

eg

Se

ns

or

Numerical Experimental

Numerical Experimental

14/17

Correlation results summary

Main outcomes from acceleration results

• very good correlation at COG in X and Z directions

• satisfactory correlation at NOSE and REAR parts

Main outcomes from pressure results

• good correlation

• impact event chronology

• pressure time history signature

• satisfactory correlation

• pressure peak values

Correlation process

model updating activity

• improvement of modelling approaches

• correction of individual parameters

15/17

Remarks and further developments

Fluid LAW51 Multimaterial with

outlet treatment SPH method

Structure Deformable body

Alternative modeling methodology

16/17

Experimental numerical results

deviation

Flexible body behaviour

Statistic data dispersion

Exposed impact areas and mathematical model

Thanks for your attention

17/17

Arbitrary Eulerian Lagrangian

• nodes fixed to material points • elements deformed as material • grid uniquely defined • instability with large deformations

Lagrangian approach

• grid fixed in space • material flows through grid • can handle large deformations • advection algorithm to reconstruct time history

Eulerian approach

• hybrid formulation • first step: grid moves as Lagrangian • second step: nodes back to original position, physical quantities

mapped and transferred with advection algorithm

ALE approach

Arbitrary Eulerian Lagrangian

ALE advantages

can handle large grid distorsion

can preserve interfaces definitions

Updating mesh

procedure

assign vel. & displ. to grid nodes at each timestep

mesh regularization to avoid excessive distorsions

Fluid structure

interaction

2 nodes at interface definition

• first to fluid • second to

structure

fluid nodes attached to structure nodes (grid velocity equal to material velocity)

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)

/MAT/LAW37/mat_ID or /MAT/BIPHAS/mat_ID

mat_title

ρi ρ0

ρl0 C𝑙 αl 𝜈l 𝜆

ρl0

ρg0 γ P0 𝜈g 𝜆

ρg0

LAW37 Biphas material card

Acceleration results summary

Accelerometer Peak acceleration Overall time history

Cog_x very good very good

Cog_z very good good

Nose_x insufficient good

Nose_z sufficient good

Rear_x insufficient sufficient

Rear_z good very good

Cog_x good good

Cog_z very good very good

Rear_x sufficient good

Rear_z good very good

Cog_x very good very good

Cog_z quite good very good

Nose_x insufficient good

Nose_z good very good

Rear_x sufficient sufficient

Rear_z very good very good

Cog_x very good very good

Cog_z good very good

Nose_x quite good very good

Nose_z quite good very good

Rear_x quite good quite good

Rear_z very good good

1°

L.c

. 2

° L

.c.

3°

L.c

. 4

° L

.c.

Pressure Peak pressure Impact

occurrence time

Overall time history

Probe 51 deg very good very good very good

Probe 35 deg sufficient very good very good

Probe 19 deg very good very good very good 1°

L.c

.

Probe 51 deg very good very good very good

Probe 35 deg good very good very good

Probe 19 deg good very good very good 2°

L.c

.

Probe 51 deg good very good very good

Probe 35 deg good very good very good

Probe 19 deg very good very good very good 3°

L.c

.

Probe 51 deg good very good very good

Probe 35 deg sufficient very good very good

Probe 19 deg good very good very good 4°

L.c

.

Pressure results summary