You can do this with something like this
Get-Cluster -Name Cluster1
| Get-VM |
Remove-VM -DeletePermanently -Confirm:$false
To make sure this actually going to do what you expect it to do, you can use the WhatIf switch on the Remove-VM cmdlet.
That way the cmdlet will tell you waht it is going to do, without actually doing it.
Get-Cluster -Name Cluster1
| Get-VM |
Remove-VM -DeletePermanently -Confirm:$false -WhatIf