knoppix@Knoppix:~$ perl -le '
@arr = qw{ ch1 ch11 ch2 ch5 ch55 ch16 };
print for
   map  { $_->[ 0 ] }
   sort { $a->[ 1 ] <=> $b->[ 1 ] }
   map  { [ $_, ( split m{(?<=\D)(?=\d)} )[ 1 ] ] }
   @arr;'
ch1
ch2
ch5
ch11
ch16
ch55
knoppix@Knoppix:~$