prefix_ptuwc_query_product_type.php

<?php
/**
 * Add different product types
 */
function prefix_ptuwc_query_product_type( $tax_query, $args, $table ) {
	$product_types = array( 'grouped' ); // Add your custom post types here as a comma separated list
	if( $tax_query ) {
		foreach( $tax_query as $index=>$arg ) {
			if( isset( $arg['taxonomy'] ) && $arg['taxonomy'] == 'product_type' ) {
				// Check the taxonomy given
				$tax_query[$index]['terms'] = array_merge( $tax_query[$index]['terms'], $product_types );
			}
		}
	}
	return $tax_query;
}
add_filter( 'ptuwc_query_tax-query', 'prefix_ptuwc_query_product_type', 10, 3 );