The following command will download a vApp from vCloud Director (8.20). Note the vApp needs to be in a stopped state.

vCloud URL:         myuatcloud.jordansphere.co.uk
Org Name:           Jordansphere
Org VDC Name:  JordansphereUAT
vApp Name:        CentOS

Username:          auser

Password:           p5word!!31

cd c:\Program Files\VMware\VMware OVF Tool 
ovftool.exe  "vcloud://auser:[email protected]?vdc=JordansphereUAT&org=Jordansphere&vapp=CentOS" "C:\backups\CentOS7.ovf"