plugin contact form 7 – Print Current User Display Name

I am trying to print the current user display name with the following. Any help how to make it work?

function filter_product_pwb_brand($value, $post_id, $form_data){
  // $value is the post field value to return, by default it is empty. If you 
  // are filtering a taxonomy you can return either slug/id/array.  in case of ids
  // make sure to cast them integers.
  // (see
  // for more information.)
  // $post_id is the ID of the post to which the form values are being mapped to
  // $form_data is the submitted form data as an array of field-name=>value pairs
  return $value;