Ritu Gavasane

Guide: Prof. Murali Damodaran

INDIAN INSTITUTE OF TECHNOLOGY GANDHINAGARDiscipline of Mechanical Engineering

VGEC Complex, Visat-Gandhinagar HighwayChandkheda, Ahmedabad, GJ 382424

INDIA

24 April 2014

B. Tech Project Presentation

Flow Modeling for High Altitude

Airships with Free and Forced

Transition Modelling

Content Problem statement

Previous work

Motivation behind present work

Computational Setup

Envelope Profile of Airship

Geometry and Computational Domain

Discretized Computational Domain

Physics: Initial and Boundary Conditions

Computational Results

Free Transition

Forced Transition

Validation of CFD Results with those of wind tunnel test

Comparison between free and forced transition

Conclusion

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Problem statement Modelling of high altitude Airship-fully turbulent

conditions

GNV Rao Airship

Modelling of ZHIYUAN-1 Airship transition modelling

Free transition

Forced transition

Validation of CFD results with experimental wind tunnel

test

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Previous work: GNV Rao Airship

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For = 100

Aerodynamic coefficients

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Motivation behind present

work Fully turbulence modelling overpredicts aerodynamic

forces

Transition modelling is absolutely essential for accurate

and near-to-practical results

Hence transition was modelled : ZHIYUAN-1 Airship

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Computational Setup: Envelope Profile of Airship

Hull configuration Fin configuration

NACA 0010 for fin cross section7

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Geometry of Airship

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strips at x/c=0.52 for

forced transition case

(a) Airship geometry for free transition case (b) Airship geometry for forced transition case

Computational Domain

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Velocity Inflow

Freestream

No Slip Boundary

Condition on Hull

surface

Mesh Discretization

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Mesh count :

0.52 millionOverlapping

mesh region

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Physics

Unsteady

Inflow velocity = 60.39

Reynolds number = 2.5106

The free stream turbulence level = 0.1 %

Turbulence modeling, K turbulence model

Transition modelling, -Re- Transition model

Simulations were performed for different angles of

attack () ranging from -300 to 300.

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Governing Equations

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Continuity Equation

Momentum Equation

Integral form of Navier Stokes equation

Computational results

Free transition

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(a) Velocity profile (b) Skin friction coefficient profile

(c) Wall Shear Stress for = 300

Aerodynamic coefficients: Free

transition

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Computational results

Forced transition

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Comparison: Free and Forced transition

Wall Shear stress

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Free transition

At =120

Forced transition

Comparison: Free and Forced transition

Skin friction

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Velocity profile: Treftz plane

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Comparison of Force Coefficients

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Videos: Free transition

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Forced transition

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Discussion All the computationally calculated force coefficients

agree well with the experimental wind tunnel tests.

Drag and Moment coefficients deviated from the

experimental values at lower angles of attack

In case of forced transition, flow separation was

observed at the position of strips on the airship hull.

The CFD results of free and forced transition did not

differ much for the assumed point of transition that was

positioned at x/c=0.52

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Thank You

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