Preheat over to 350 degrees. Grease and flour 9x13 inch pan. Prepare cake mix as directed. Pour batter into pan. In medium bowl mix together rhubarb and sugar. Spoon over top of cake batter. Drizzle whipping cream over top of rhubarb. Bake for 40 minutes or until toothpick comes out clean. Let cake cook completely before serving.  I top the cake with cool whip when I serve it.