Smoke simulation values are Resetting automatically I simulated smoke in Blender 2.74 and when I changed vorticity to 3 and changed flow type to smoke+fire which is in next tab the vorticity value again changed to default value. Then I tried Alt+A and there is no simulation. and all the values are resetting automatically.
This is because you are turning the domain  into an emitter and then back into a domain.

Each smoke type (domain, flow, collision) plays a different role in the simulation with different settings. By clicking that button, you are changing the active object to a different type.

Generally you'll want to select one of the smoke types for each object and leave them at that. Domain options should be set on the domain object and flow settings set on the flow object(s).

For example, here's a quick setup:



Note that to access the different settings for the domain and flow objects I select the object in question.