Experimental Investigation of the Unsteady Discharge Flow in a Centrifugal Impeller with Splitter Blades

The discharged flow characteristic from an unshrouded centrifugal impeller with splitter blades is experimentally investigated.The effects of the main blade and the splitter blade on the unsteady flow quantities are analyzed.An X-type hot-film anemometry is used to measure the flow quantities at the impeller outlet and diffuser inlet in three spanwise positions.The result shows that the difference between the splitter and main blade effects on flow becomes most significant at the mid-span position.At the impeller outlet near the main blade wake region,the radial velocity reduces by 62%,the tangential velocity increases by 2%,and the absolute flow angle decreases by about 8 degrees,comparing with that near the splitter blade wake region.At the diffuser inlet,the difference between the splitter and the main blade wake regions is still visible though it has been weakened.The base frequency of the unsteady flow is a main blade or a splitter blade passing frequency.The base and second harmonics exert dominating effects on the unsteady flow.Reynolds stress levels in the discharged flow from the main blade are higher than that from the splitter blade.Especially in the mid-span region,the Reynolds stress difference reaches to 68%.The absolute outflow angle changes more than 10 degrees in the spanwise,which indicates that separating or rushing loss may be produced in the present two-dimensional vaned diffuser,so a three-dimensional vaned diffuser seems to become necessary.