Because of the size of the stars the fluid motions are characterized by very high Reynolds numbers which means that the flows are turbulent. This turbulence is the basic difficulty which astrophysicist must face to model solar-type stars. Making progress is very hard because we have no general theory of turbulence at hand. One way in this jungle is to do direct simulations of these flows (using Reynolds number around 1000), understand the important properties of these flows and then extrapolate to the real sun where the Reynolds number is 10^12. Then we may test our results and conjectures on some observables like the differential rotation or the magnetic activity of the sun.

More on direct simulations:

- Nordlund A., Brandenburg A., Jennings R., Rieutord M., Ruokolainen J., Stein R. and Tuominen I. (1992), "Dynamo action in stratified convection with overshoot", Astrophysical Journal vol. 392, pp.~647--652.
- Rieutord M., Brandenburg A., Mangeney A. and Drossart P. (1994), "Reynolds stresses and differential rotation in Boussinesq convection in a rotating spherical shell", Astronomy and Astrophysics vol. 286, pp.~471--480.
- Brandenburg A., Jennings R., Nordlund A., Rieutord M., Stein R. and Tuominen I. (1996), "Magnetic structures in a dynamo simulation", Journal of Fluid Mechanics vol. 306, pp.~325--357.

More on extrapolation:

- Rieutord M. and Zahn J.-P. (1995), "Turbulent plumes in stellar convective envelopes", Astronomy and Astrophysics vol. 296, pp.~127--138.
- Bonin P. and Rieutord M. (1996), "The dynamics of turbulent plumes in a stellar convective envelope", Astronomy and Astrophysics vol. 310 pp.~221--227.