Adv Dm v6.3 06a Coupled Flow

6DOF Solver and 1DOF 6DOF Solver and 1DOF 6DOF Solver and 1DOF UDF6DOF Solver and 1DOF UDF

Advanced FLUENT DynamicAdvanced FLUENT DynamicAdvanced FLUENT Dynamic Mesh TrainingAdvanced FLUENT Dynamic Mesh Training

© 2008 ANSYS, Inc. All rights reserved. ANSYS, Inc. Proprietary

Fluent User Services Center

www.fluentusers.comAdvanced Dynamic Mesh TrainingFLUENT v6.3 January 2008

6 DOF Solver – Introduction

S f h l d ib d ti ifi d thSo far, we have only used prescribed motion – we specified the location or velocity of the object using the in-cylinder tool or a profile.Now we would like to move the object as a result of the aerodynamic forces and moments acting together with other forces such as the forceforces and moments acting together with other forces, such as the force due to gravity, thrust forces, or ejector forces (i.e., forces used to initially push objects away from an airplane or rocket, to avoid collisions). The motion and the flow field are thus coupled, and we

ll hi l d icall this coupled motion.Store separationStage separation

Fluent provides a 6DOF solver that computes the trajectory of anFluent provides a 6DOF solver that computes the trajectory of an object based on the aerodynamic forces/moments, gravitational force, and ejector forces. Fluent also provides a 1DOF UDF for 1 degree of freedom coupled

6-2© 2008 ANSYS, Inc. All rights reserved. ANSYS, Inc. Proprietary

Fluent also provides a 1DOF UDF for 1 degree of freedom coupled flow



6 DOF UDF – Theory

U d fi l t i th lUser defines several parameters in the panelGravitational forceInitial conditions including CG location, CG orientation, CG linear velocity, and CG angular velocityvelocity, and CG angular velocity

User also defines the following parameters in a UDF. A UDF is used so that they can be a function of time

Mass and momentum of inertia. Ejector forces (optional)

Fluent will compute the aerodynamic forces and momentsBased on the force balance (aerodynamic, gravity, and ejector forces), compute the translational acceleration, then integrate to calculate the translational velocity. Based on the moments, compute the angular acceleration, then integrate to calculate the angular velocity.Compute the new CG location and Euler angles


Compute the new CG location and Euler angles



Example 1 – 2D Store Separation

A l 6 DOF l h i d f h dApply 6 DOF solver to the airdrop of the rescue podBelow is the UDF used to specify the mass matrix and ejector force:

#include "udf.h"

DEFINE_SDOF_PROPERTIES(store, prop, dt, time, dtime)

{

/* Define the mass matrix */

prop[SDOF_MASS] = 5000.0;p p[ ] ;

prop[SDOF_IZZ] = 5e3;

/* add ejector forces, moments */

if (time <= 0.3)

{{

prop[SDOF_LOAD_F_X] = -40000;

prop[SDOF_LOAD_F_Y] = -80000;

prop[SDOF_LOAD_M_Z] = -2200.0;

}


}

Message0("\nUpdated 6DOF properties\n");

}



Example 1 – DM Parameters

S l t Si DOF S lSelect Six DOF SolverEnter Gravitational AccelerationSmoothing and Remeshing parameters are the same as in the non-coupled case




Example 1 – Dynamic ZonesT d iTwo dynamic zones

Wall-object: rigid body motion plus initial conditionFluid-bl: identical setup as wall-object except for Passive




Example 1 – Mesh Motion

E i ithEven in cases with coupled motion, it is wise to preview the mesh motion before performing p gthe calculations.In this case, start without initializing, and the object

ill i l d d hwill simply drop under the influence of gravity and/or external forces.Observe the effect ofObserve the effect of dynamic mesh parameters (spring constant, size function, maximum


skewness, etc.)



Example 1 – Animation

Th fi hThe figure shows pressure contours corresponding to a freestream Machfreestream Mach number of 0.8 Note how the object has drifted aft and how itdrifted aft, and how it goes forward at the beginning due to ejector forceforceThis problem exists as a tutorial.




Example 2 – 3D Store Separation

St d dStore dropped from a delta wing (NACA 64A010) at Mach 1.2.Ejector forces dominate for a short time.All-tet mesh.Smoothing. remeshing with i f tisize function.

Fluent results agree very well with wind tunnel


with wind tunnel results!



Example 3 – 2D Store Separation with VOF




Example 2 – 2d Rocket Stage Separation




1DOF UDF

Si il 6DOF l UDF i i f 1DOF l d flSimilar to 6DOF solver, a UDF is written for 1DOF coupled flowLagrange gunCheck valve

The 1DOF UDF also considers the min and max distance that the object can travel, which is normally important for 1DOF application.

Note that the 6DOF solver will not consider the boundary. The user needs k h h bj hi b dto make sure that the object never hits any boundary

Pure layering is normally used for 1DOF application. For 6DOF applications, pure tri/tet mesh is normally used.Tutorial exists for 1DOF UDF




Example 1 – Missile Silo Launch




Example 2 – Muzzle Brake

P j il iProjectile moving inside and out of a barrel.I i i l h i hInitial patch in the chamber drives the motion.U d fi d lUser-defined real gas law (Abel-Nobel Equation of State).L iLayering.Tutorial exists.




Example 2 – Results

I i i l h i Fi l di i h iInitial patch in the chamber drives the motion of the 50 kg

Final condition at shot exit

of the 50 kg bullet/piston.User-defined real gas law (Abelgas law (Abel-Nobel Equation of State).Very goodVery good agreement (red and green data) all the way to

Initial condition at time t = 0


all the way to shot exit!



6 DOF Coupled Motion – Tips

E i i h l d i i i i i h hEven in cases with coupled motion, it is wise to preview the mesh motion before carrying out the flow calculations (which can be expensive).

S ti d ith t i iti l li / l l it dSometimes you can proceed without initial linear/angular velocity, and observe a linear motion in the direction of the gravity vector.Other times, it may be useful to provide an initial condition in order to impart initial translational and/or rotational velocity componentsimpart initial translational and/or rotational velocity components.It is usually better (but more expensive) to compute a steady solution in order to obtain an initial distribution of pressures and shear stresses.

After convergence, switch to the unsteady solver and hook the UDF.g yDuring the preview, the object will move based on the forces that resulted from the steady calculation. The resulting motion usually involves both translation and rotation.




6 DOF Coupled Motion – Tutorial

A hi i d h d f 6DOF i lAt this time we recommend that you do on of our 6DOF tutorials2D Store Separation – Air Drop of a Rescue Pod3D Store Separation – Delta Wing


Adv Dm v6.3 06a Coupled Flow

Documents

Transcript of Adv Dm v6.3 06a Coupled Flow