Radial Inflow/Mixed Flow Turbine Impeller Design

TURBOdesign Applications

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Fig.1 Specified loading


Fig.2 Resulting blade shape of Radial inflow turbine


Fig.3 Mixed flow turbines

TURBOdesign-1 can been applied to improve the design of radial and mixed flow turbines. Some examples of improvements achieved with TURBOdesign-1 include:

The loading distribution shown in Fig.1 was used for the design of a radial-inflow turbine for Micro gas-turbine applications. The resulting blade geometry is shown in Fig.2. Detailed CFD computations showed that this impeller has less meridional secondary flows on the suction surface and a more uniform exit flow.

The test results indicated a 5 point improvement in efficiency as compared to the conventional design.

TURBOdesign-1 can be applied with ease to the design of all types of mixed flow turbines impellers as well. An example of one such impeller is shown in Fig.3.

Zangeneh, M, 1990 " Three dimensional design of a high speed radial-inflow turbine by a novel design method". Presented at the 35th ASME/IGTI International Gas Turbine conference, Brussels. ASME Paper 90-GT-235, pp. 1-8.
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Watanabe., 2004, "Optimization of Microturbine Aerodynamics using CFD, Inverse Design and FEM Structural analysis (2nd report: Turbine Aerodynamics)", ASME Paper GT2003-53583.

Radial Inflow Turbines

Barber-Nichols Inc. (BNI) specializes in the engineering, manufacturing, and testing of Radial Inflow Turbines. The radial flow turbine when applied in the proper expansion conditions can achieve extremely high efficiencies, equaling or exceeding that of axial flow turbines. The radial inflow turbine is a robust design that is economical to engineer and produce and can provide years of service.

Radial InflowA Radial Inflow Turbine infers that the working fluid passes from the outer diameter of the turbine assembly inward and exits the turbine rotor at a smaller diameter. The incoming fluid usually passes through a set of nozzles that cause the fluid to swirl and thereby entering the turbine rotor at the proper relative velocity. The flow then continues through the rotor where it continues to expand and impart energy to the rotor. The fluid then leaves the rotor near the rotational centerline. The blade angles at the rotor exit are designed to remove exit swirl as the fluid leaves the machine. This minimizes the energy in the exhaust flow thereby increasing the turbine efficiency. In some designs the inlet nozzles are replaced with an inlet scroll sized to provide the swirl to the rotor.

The most common application for the radial inflow turbine is the exhaust driven turbocharger used on internal combustion engines. Thousands of these units are used in automobiles, aircraft, and industrial engines, both diesel and gasoline fueled. Other applications include power generation by gas turbines or by expanding organic fluids in a Rankine cycle. Finally, Radial Inflow Turbines are also used in process plants to recover heavy hydrocarbons from gas streams.

Radial Inflow Turbines have very high efficiencies when applied in the proper operating conditions. Specific Speed (Ns), a dimensionless parameter, can be used to determine whether or not a Radial Inflow Turbine will fit your application. If the Ns is between 30 and 120 a Radial Inflow Turbine's efficiency will be comparable or even greater than a conventional axial flow turbine. The most commonly used definition of Ns (using US customary units) is:

N S = RPM (Q) 1/2 / H 3/4

( Where Q = ft 3 /sec & H = Feet of Head Across the Turbine )

Radial Efficiency

The implementation of impulse blades cantilevered on the side of the rotor disk is an alternate Radial Inflow Turbine configuration that is useful at slower specific speeds. This configuration will have a small amount of reaction resulting from the radius change between the inlet and the outlet of the blade row. BNI has utilized this turbine configuration and achieved extremely high performance levels. Thank you for your interest in Barber-Nichols and we hope that we can put our expertise and experience to work for you.