  The Lyman continuum (LyC) escape fraction is a key quantity to determine the
contribution of galaxies to cosmic reionization. It has been known that the
escape fractions estimated by observations and numerical simulations show a
large diversity. However, the origins of the diversity are still uncertain. In
this work, to understand what quantities of galaxies are responsible for
controlling the escape fraction, we numerically evaluate the escape fraction by
performing ray-tracing calculation with simplified disc galaxy models. With a
smooth disc model, we explore the dependence of the escape fraction on the
disposition of ionizing sources, and find that the escape fraction varies up to
$\sim 3$ orders of magnitude. It is also found that the halo mass dependence of
disc scale height determines whether the escape fraction increases or decreases
with halo mass. With a clumpy disc model, it turns out that the escape fraction
increases as the clump mass fraction increases because the density in the
inter-clump region decreases. In addition, we find that clumpiness regulates
the escape fraction via two ways when the total clump mass dominates the total
gas mass; the escape fraction is controlled by the covering factor of clumps if
the clumps are dense sufficient to block LyC photons, otherwise the clumpiness
works to reduce the escape fraction by increasing the total number of
recombination events in a galaxy.
