Why i cant see computer by name in deferent VLAN only by IP (Dont have local DNS)

HI,

I have fortiwifi40F fortiswicth, we created SSID wifi network, and another VLAN for the LAN users.

We dont have local DNS so we are using public DNS in both networks 

But we cant map or see the computers in the LAN, from the WIfi network with the computer name only IP address when we need to map the shared drive 

I know we can create Software switch and add both the wifi, and lan to the same network but we need to separate the network 

Why i cant see the computer with name ?