Aerothermodynamics Investigations for Earth orbital entry vehiclesEhemaligen –Treffen DLR, June 16 2005

Ph. ReynierAOES - ESTEC / TEC-MPA

2

• Presentation of ESA-ESTEC and AOES.

• Main features of my activities.

• Technical activities for a project: IRDT

Outline

3Austria

Belgium

Denmark

France

Germany

Ireland

Italy

Netherlands

Norway

Spain

ESA replaced the former Eldo launcher and Esro satellite organisations, grouping the complete range of civilian

space activities in a single agency

Portugal joined as 15th member state in 2000

Greece joined as 16th member state in 2005

Cooperation arrangement: Canada

Sweden

Switzerland

United KingdomPortugal

Finland

Greece

4

• Basic activitiesStudies of future projects, technological research, common technical investments (facilities, laboratories, infrastructure), education.

• ScienceScientific missions: solar system science, astronomy andfundamental physics.

• Applications

Satellites and services for:– Telecommunications, navigation, data relay;– Earth observation including climatology and meteorology to monitor

land, oceans and the atmosphere.• Launchers: Ariane, Vega.

• Human spaceflight and Exploration: various elements for the International Space Station, Microgravity research and AURORA Programme.

5

(Status: May 2002)

GEN 15 - July 2002

Noordwijk, The Netherlands(European Space Research

andTechnology Centre)

Project management, testing of spacecraft,development of new technologies,space scienceStaff: 1052

Paris, France

Incl. offices in Brussels, Toulouse, Kourou, Moscow, Washington, HoustonStaff: 388

Kourou, French Guiana

Europe’s Spaceport for Ariane launches

Cologne, Germany(European AstronautCentre)

Astronaut trainingStaff: 21

Darmstadt, Germany(European Space Operations Centre)

Satellite operationsStaff: 232

Frascati, Italy

Earth Observation,Data Processing and DistributionStaff: 147

6ESTEC 01 - July 2002

7

• Studies, preparation and management of most ESA space programmes: science, applications (telecommunication, navigation and Earth observation), human spaceflight and microgravity research.

• Technical support to ESA project teams, incl. preparation andcoordination of ESA space technology R&D programme.

• Product assurance and safety responsibility for ESA space programmes.

• Management of ESTEC Test Centre and coordination with other test centres in Europe.

• Appr. 2000 persons (of which 1100 as international ESA staff).

8

MannedSpaceflight

andExplorationApplications

EarthObservationScience

Project Management Teams

Mechanical Engineering

Electrical Engineering

Product Assurance andSafety

Ground SystemsEngineering

9TOS 04 - May 2002

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GROUND SYSTEMSENGINEERING DEP.

PRODUCT ASSURANCE& SAFETY DEP.

ELECTRICALENGINEERING DEP.

MECHANICALENGINEERING DEP.

DATA SYSTEMSINFRASTRUCTURE

DIVISION

REQUIREMENTS& STANDARDS

DIVISION

ELECTROMAGNETICSDIVISION

MECHATRONICS& OPTICS DIVISION

MISSION DATASYSTEMS DIVISION

QUALITY,DEPENDABILITY AND

SAFETY DIVISION

MATHEMATICS& SOFTWARE DIVISION

THERMAL &STRUCTURES DIVISION

GROUND STATIONSYSTEMS DIVISION

COMPONENTSDIVISION

POWER & ENERGYCONVERSION

DIVISION

PROPULSION &AEROTHERMODYNAMICS

DIVISION

FLIGHT DYNAMICSDIVISION

MATERIALS &PROCESSES

DIVISION

CONTROL& DATA SYSTEM

DIVISION

TESTING &ENGINEERING

SERVICES DIVISION

NAVIGATIONSUPPORT OFFICE

PROJECT & TECHNICALREVIEWS OFFICE

PAYLOAD SYSTEMSDIVISION

MULTIDISCIPLINARYRE-ENTRY VEHICLE

TECHNOLOGIES& SPECIAL PROJECTS

OFFICEMISSION ANALYSISOFFICE

SPECIAL PROJECTSOFFICE

ERASMUS FRCOFFICE

10

• Provides Engineering Services, Information Technology, and Visual and Technical Communication to the Aerospace and Automotive Industry:

- Space Engineering;- Aircraft Engineering;- Medialab;- CAE and Information Technology

Services.

• Around 100 persons. • Offices in Leiden (NL), Francfort and Munich.

Advanced Operations and Engineering Services

11

• Consulting engineer with the Aerothermodynamics Section at ESTEC and the following tasks:

- Technical support of projects (ExoMars, PARES, ATV, IRDT) including participation to reviews of industry work.

- Support to prepare the R&T Programmes of ESA (TRP, GSTP).

- Support for technology roadmap and aerothermodynamics activities for AURORA Programme (Mars exploration).

Activities

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• Developments carried out for IRDT but also in the perspective of future developments.

• Aerothermodynamics analysis to prepare IRDT-2R mission and post-flight analysis.

• The focus has been put on some specific aerothermodynamics aspects of IRDT mission.

Objectives of the study

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IRDT Mission Scenario

Credit to BSC, EADS & ESA.

14

IRDT Geometry

15

• Selected points are:

– Trajectory analysis

– Flow-field

– Heat-flux

– Blackout

– Transition to turbulence

Focus of the study

16

• Entry parameters at 100 km , t = 906 s (from launch):

– V = 6869 m/s

– Lat. 60.88 º N

– Long. 159.2 º E

– Fpa = -6.84º

• Rebuilding with Traj3D and comparisons with the predictions of Babakin Space Center (BSC).

Trajectory Analysis - 1

17

• Trajectory from 100 km to 7.5 km where AIBD is inflated.

• Maximum discrepancy for altitude is 3%.

Trajectory Analysis - 2

time (s)

Alti

tude

(m)

900 1000 1100 1200 13000

20000

40000

60000

80000

100000

ESTECBSC

18

Trajectory Analysis - 3

time (s)

G-lo

ad(m

2/s

-2)

900 1000 1100 1200 1300-20

-15

-10

-5

0

ESTECBSC

time (s)

q(k

W/m

2)

900 925 950 975 10000

100

200

300

400

500

600

700

ESTECBSC

g-load and heat-flux distributions along IRDT trajectory. For the heat-flux: BSC = BL + Cold Wall; ESTEC = Detra & Hildago + Cold Wall.

19

• Maximum difference for g-load and heat-flux is around 8%.

Due to some different atmosphere model used for the two calculations; Verification on-going.

• Maximum of convective heat-flux occurs 43 s after re-entry beginning. First order approximation shows that radiative flux is negligible.

Trajectory Analysis - 4

20

• Communications insured by an Autonomous Radio Transmitter System during the mission.

• Antenna operating at 219 MHz (UHF band) embedded in the heat-shield.

• First order assessment: diffraction, coupling with radiation and electromagnetic wave propagation within a plasma are beyond the scope of this study.

Blackout - 1

21

• Critical electronic density ne,crit for ARTS frequency fp:

where q is the electron charge, me the electron mass and ε0 the permittivity of vacuum. Then,

Blackout - 2

,0

,2

21

e

critep m

nqf

επ=

6

2

, 10.64.80p

crite

fn =

22

• Calculation of the electronic density along the trajectory.

• Usually, minor differences are found between 2D and 3D calculations for blackout predictions.

• Performed with PMSSR (inverse technique) using an inviscid axisymmetric approach at thermal and chemical non-equilibrium.

• Model from Park (1993) with 11 species (N2, N2+, N, N+,

O2, O2+, O, O+, NO, NO+, e- ) and 16 reactions.

Blackout - 3

23

• Electronic density along the trajectory and critical electronic densities for several bands.

• Blackout for ARTS lasts 60 s here and 80 s for BSC (the entry duration).

But BSC has taken a margin of 20 s on the entry time.

Blackout - 4

Time (s)

Ele

ctro

nic

Den

sity

(e/c

m3)

900 920 940 960 980105

106

107

108

109

1010

1011

1012

1013

PMSSRKa BandX BandS BandARTS Band

24

• Transition onset is dominated by the amplification of instability modes. When they are sufficiently amplified, a 3D bifurcation leads to a transitional flow.

• In re-entry flows, transition is driven by surface micro-roughness elements.

• For a preliminary study, the prediction of transition is achieved using engineering methods:

Here, Traj3D associated to transition criteria

Transition to turbulence - 1

25

• Transition criterion for a smooth surface:

Reθ, where θ is the boundary layer momentum thickness.

• The critical value of Reθ, for entry blunt bodies varies in the literature from 140 to 250,

Here, a value of 140 is retained.

Transition to turbulence - 2

26

• Evolution of ReD and Reθ,along the IRDT reentry trajectory.

• For a smooth surface the transition threshold is reached at t=1106 s quite late after the peak of heat-flux (t= 969 s).

Transition to turbulence - 3

Time(s)900 1000 1100 1200 13000

50

100

150

200

250

300

350

400

450

10 e-4 Re (D)Re(Theta)Transition threshold

27

• IRDT geometry is characterized by two backward facing steps favouring transition.

• The entry is ablative,

Additional roughness,

Blowing at the surface might have an additional destabilizing effect on the boundary layer.

• According to Reda, for an ablative entry, transition location for the flight is considerably earlier than predicted by the usual correlations.

Transition to turbulence - 4

28

• Transition criterion for a rough surface:

Derived by Reda from the PANT criterion.

PANT criterion:

Reda criterion:

where k is the surface roughness, Te, ρe, Ue and µe are the temperature, the density, the velocity and the dynamic viscosityat the boundary layer edge and Tw the temperature at the wall.

Transition to turbulence - 5

255Re7.0

≥��

���

�

w

e

T

Tk

θθ

106Re ≅��

���

�=

TRe

eek

kU

µρ

29

• Reda criterion has an uncertainty of 20 %.

• The transition threshold is reached at the early age of the re-entry for k =1mm,

The smallest step along IRDT is 10 mm.

Transition to turbulence - 6

Time(s)

Re(

k)

900 1000 1100 1200 13000

100

200

300

400

500

600

700

800k = 0.1 mmk = 0.5 mmk = 1 mmk = 2 mmk = 10 mm

30

• According to the criterion used, transition is most likely to happen during IRDT mission.

• Reda criterion has been validated for carbon-based TPS materials,

Validity for silica based materials is questionable.

• A turbulent flow might increase the heat-flux by 50 %.

TPS has been designed by BSC accounting for the maximum of heat-flux between a laminar and a turbulent flow.

Transition to turbulence - 7

31

• 2D and 3D Navier-Stokes computations performed with TAU (code from DLR) for an unstructured hybrid mesh (tetrahedra + prisms),

Main objective is to analyse the flow at the backward facing step locations.

• Time integration is carried out with a Runge-Kutta method. Flux computed with the AUSM-DV scheme. Scheme is 2nd order accurate in space.

Flow-field - 1

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• Grid generated with Centaur.

• Grid independence reached with the adaptation module of TAU,

900000 tetrahedra, 300000 prisms.

Flow-field - 2

Adapted grid for 3D computations.

33

• Laminar predictions without angle of attack for a fully catalytic wall at 1500 ºK.

• Thermochemical effects accounted for with a 5 species (N2, N, O2, O, NO) air model and 17 chemical reactions.

• Ionisation is not considered.

Flow-field - 3

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• Computations performed for the trajectory point corresponding to the peak of heat-flux:

- Altitude: 66 km

- Pressure: 14.1 Pa

- Density: 2.10-4 kg/m3

- Temperature: 245ºK

- Velocity: 5817 m/s

Flow-field - 4

Mach number distribution.

35

• Vorticity

Three separated bubble flows over the cone and MIBD. The second is produced by a local maximum of pressure due to the first recompression shock.

This succession of separated zones will play a destabilizing effect on the boundary layer.

Flow-field - 5

Zoom of vorticity distribution.

vorticity9.5E+05

7.5E+05

5.5E+05

3.5E+05

1.5E+05

Vorticity field at Mach 18.5

36

• Heat-flux over IRDT:

Value at the stagnation point close to the one predict by the trajectory code;

Influence of the two steps over the geometry.

Heat-flux - 1

Z(m)

Q(k

W/m

2)

0 0.2 0.4 0.6 0.8 1 1.20

200

400

600

800

1000

37

• Pressure and heat-flux over IRDT:

Good correlation between the curves at the two backward facing steps.

Heat-flux - 2

Z(m)

Q(k

W/m

2)

P(P

a)

0 0.5 10

200

400

600

800

1000

0

1000

2000

3000

4000

5000

6000

7000

38

• 2D computations performed with TINA (code from FGE) with a structured mesh and the Roe solver,

Main objective is to estimate the ionisation influence on the heat-flux.

• Laminar predictions without angle of attack for a fully catalytic wall at 1500 ºK.

• Thermochemical effects accounted for with a 11 species (O2, O2+, N2, N2+, N, N+, O, O+, NO, NO+, e-) and 21 reactions air model (Roberts, FGE, 1994).

Heat-flux - 3

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• Ionisation

- High influence on the level of heat-flux.

- Need of a code to code comparison based on the same thermochemical model.

Heat-flux - 4

Z(m)

Q(k

W/m

2)

0 0.2 0.4 0.6 0.8 10

200

400

600

800

1000

TAUTINA

Heat-flux distributions with TAU and TINA.

40

• Need to use the same model for a code-to-code comparison and validation.

• IRDT heat-shield is ablative and based on silica,

Need to account for ablation for heat-flux predictions.

Silica melts during entry, the presence of a liquid film is a potential issue.

Heat-flux - 5

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• Elements for aerothermodynamics analysis of IRDT re-entry and good agreement with BSC analysis.

• Needs for further investigation accounting for turbulence, ionisation and ablation to estimate more accurately the heat-flux.

• Computations of the configuration with angle of attack.

• In order to improve tool capabilities, flight data and numerical rebuilding are a key issue.

Conclusions

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• Knowledge of the German aerospace agency and industry.

• Working experience in a German research centre and confrontation to another culture.

• Discovery of an unstructured code: TAU.

Usefulness of DLR time

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• Take advantage of DLR time, here you can take the time to really learn your job, you do not have the stress of industry.

• Gain working experience abroad: A complete immersion is better.

• Put more efforts to learn foreign languages that I did for German…………..

Recommendations

44M�: Million of Euro

L: 0.10%, 7.5 M�

IRL: 0.26%, 7.5 M�

I: 13.27%, 378.4 M�

NL: 2.38%, 67.7 M�N: 0.87%, 24.8 M�

E: 3.76%, 107.2 M�S: 1.93%, 54.9 M�

CH: 2.84%, 81.1 M�UK: 6.4%, 182.6 M�

CND: 0.58%, 16.5 M�

A: 0.91%, 26.1 M�

D: 23.1%, 659 M�

CZ: 0.01%, 0.3 M� B: 4.74%, 135.1 M�

DK: 0.98%, 28 M�

FIN: 0.45%, 12.8 M�

F: 26.69%, 761.4 M�P: 0.36%, 10.1 M�

Income from member states :2 556.4 M�Other income : 296.0 M�

Total: :2 852.4 M�

Income fromMember States

2 556.4 M�

BUD 01 - Mar 2002

(ref.: ESA/AF-01/2002)