Adaptive linear second-order energy stable schemes for time-fractional Allen-Cahn equation with volume constraint

•A volume-preserving time-fractional Allen-Cahn model is developed.•Adaptive linear second-order energy stable schemes are developed.•The proposed adaptive time-stepping algorithms are appropriate for accurately resolv- ing the initial singularity of solution and for efficiently capturing the fast dynamics away initial time. A time-fractional Allen-Cahn equation with volume constraint is first proposed by introducing a nonlocal time-dependent Lagrange multiplier. Adaptive linear second-order energy stable schemes are developed for the proposed model by combining invariant energy quadratization and scalar auxiliary variable approaches with the recent L1+ formula. The new developed methods are proved to be volume-preserving and unconditionally energy stable on arbitrary nonuniform time meshes. The accelerated algorithm and adaptive time strategy are employed in numerical implementation. Numerical results show that the proposed algorithms are computationally efficient in multi-scale simulations, and appropriate for accurately resolving the intrinsically initial singularity of solution and for efficiently capturing the fast dynamics away initial time.