What is the mechanism of turbulence? Will there be turbulence without viscosity?

Because viscosity is the cause of turbulence, the external flow problem can only solve Euler equation, and the internal flow problem must solve ns equation because of the influence of turbulence. But I don't quite agree with him. I think turbulence is an inevitable phenomenon brought by the increase of fluid velocity, which has nothing to do with viscosity. Viscosity is just a property of fluid. So my idea is that the ideal fluid also has turbulence, so the internal flow problem can also be solved only by Euler equation. To put it simply, although the boundary layer theory thinks that the viscosity is only in the layer and there is no viscosity outside the layer to solve the Euler equation, it is an assumption, and in many cases (such as unsteady, specific geometry and complex geometry), this assumption is not valid, and the influence of viscosity involves the whole flow field, so the Euler equation cannot be solved simply outside the boundary layer. In addition, CFD is usually easier to solve viscous problems than non-viscous problems.