POLITECNICO OF TURIN

MASTER DEGREE THESIS IN AEROSPACE ENGINEERING

Study on structural behavior of an atmosphericreentry vehicle during ditching

Supervisors:

• Prof. Giulio Romeo – Politecnico of Turin

• Ing. Roberto Ullio – Thales Alenia Space

Candidate• Maurizio Coltro

Part of ESA’s Future Launchers Preparatory Programme has been devoted to optimizing a long-term European roadmap for in-flight experimentation with atmospheric re-entry enabling systems and technologies.

Thesis activity

The Intermediate eXperimental Vehicle (IXV) project is the next core step of this effort.

This work has been developed within the IXV project and with closed collaboration of TAS-I and ESA.

Many thanks to ESA and TAS for their support. Thanks also to Altair Engineering for providing the software suite for the analysis.

The IXV Project

Technology platform

• Intermediate element of technology-effective and cost efficient Europeanroadmap

• Prepare future ambitious operational system developments with limited risksfor 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 data1/17

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

• RadiossBLOCK V10

Solver• Hyperview

Postprocessor

Explicitsolutiontecnique

DrawbacksSuited for problems

• short duration• high velocity• highly nonlinear

nature

3/17

IXV numerical model

STRUCTURE CONFIGURATION

Fuselagecomponents

Flaps assembly

MODELING ASSUMPTIONS

External dimensions takeninto account

Bidimensional rapresentationof surfaces

Rigid body description

RIGID BODY INERTIAL PROPERTIES

Mass Jxx Jyy Jzz

[kg]

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 dimensionsto 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

Finest mesh normal to

phenomenon

Sensitivityanalysis

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

FLUID STRUCTURE INTERFACE

TYPE18

STFAC

Interface stiffness

GAP

Activationdistance

• Single TYPE18 interface torepresent 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 LoadcaseA

X-

CO

GA

Z -

CO

G

-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 All curves normalized to 1

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

AZ

-C

OG

Numerical

Experimental

12/17 All curves normalized to 1

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

AZ

-C

OG

Numerical

Experimental

13/17 All curves normalized to 1

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

gS

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

gS

en

so

r5

1 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

Correlationprocess

model updating activity

• improvement of modellingapproaches

• correction of individualparameters

15/17

Remarks and further developments

FluidLAW51 Multimaterial with

outlet treatmentSPH method

StructureDeformable body

Alternative modeling methodology

16/17

Experimentalnumerical results

deviation

Flexible body behaviour

Statistic data dispersion

Exposed impact areas andmathematical model

Thanks for your attention

17/17