Pre-select Group Audience for Organic Groups
You can use Field Permission module to not allow a user to see the group field on content type.
Use  hook_form_BASE_FORM_ID_alter() to set a default field value for group field based on current logged in user.


as a sample code (not tested)

function mymodule_form_node_form_alter(&amp;$form, &amp;$form_state) {
  $node = $form_state['node'];
  if (!isset($node-&gt;nid) || isset($node-&gt;is_new)) {
    global $user;
    $groups = og_get_groups_by_user($user);
      if(is_array($groups)) {
      // This needs to be evaluated to check proper mapping of what field expect to set a default default field value
      $form['group_field_name']['#default'] = $groups[0];  
      }
  }
}