The asymptotics of a generalised Struve function

A generalised Struve function has recently been introduced by Ali, Mondal and Nisar [J. Korean Math. Soc. {\bf 54} (2017) 575–598] as $$(\frac{1}{2}z{)}^{\nu +1}\sum _{n=0}^{\mathrm{\infty }}\frac{(\frac{1}{2}z{)}^{2n}}{\mathrm{\Gamma }(n+\frac{3}{2})\mathrm{\Gamma }(an+\nu +\frac{3}{2})},$$ where $a$ is a positive integer. In this paper, we obtain the asymptotic expansions of this function for large complex $z$ when $a$ is a real parameter satisfying $a>-1$. Some numerical examples are presented to confirm the accuracy of the expansions.