## Fluids

Topics relate to Fluent, CFX, Turbogrid and more

#### Difference between Standard earth gravity and Acceleration

• happykiran
Subscriber

Hi,

Recently I was working with a problem where point mass and gravity are considered. but instead of Gravity, I applied acceleration in the upward direction and the results are same. unable to understand which is correct either gravity or acceleration?

• peteroznewman
Subscriber

Gravity is always 9.8 m/s^2 and you can point it in six directions.

Acceleration can be any number and you can point it in any direction.

If you make Acceleration 9.8 m/s^2 in the +Y direction, that is identical to Gravity in the -Y direction.

• happykiran
Subscriber

Thank you, Peter, for the clarification. But my question is that y Acceleration should be applied in +Y direction which is the same as -Y direction of Gravity. is there any supporting documents (Or theory which proves).

• peteroznewman
Subscriber

You can build a simple model to demonstrate. Make a cube, use a fixed support on the bottom, add -Y gravity, solve and request the reaction force at the fixed support. Suppress gravity and apply a +Y acceleration of 9.8xxxxx m/s^2 (there are more digits you can see in the Gravity field), solve and look at the reaction force. It will be the same.

It's just a sign convention.  If you use FLUENT, the sign convention for acceleration is opposite, you use -Y acceleration of 9.8 m/s^2 to create the effect of gravity.

• happykiran
Subscriber

Thanks Peter