  The renormalization ideas of self-similar dynamics of a strongly turbulent
flame front are applied to the case of a flame with realistically large thermal
expansion of the burning matter. In that case a flame front is corrugated both
by external turbulence and the intrinsic flame instability. The analytical
formulas for the velocity of flame propagation are obtained. It is demonstrated
that the flame instability is of principal importance when the integral
turbulent length scale is much larger than the cut off wavelength of the
instability. The developed theory is used to analyse recent experiments on
turbulent flames propagating in tubes. It is demonstrated that most of the
flame velocity increase measured experimentally is provided by the large scale
effects like the flame instability, and not by the small-scale external
turbulence.
