A Test Facility for the Investigation of Steady and Unsteady Transonic Flows in Annular Cascades

A unique non-rotating aerodynamic test facility is presented. It is designed for steady and unsteady transonic flow investigations in annular cascades. The fundamental advantage of this vehicle design, compared to a linear cascade facility, is the absence of boundary disturbances in the cascade and the self-adjustment of the flow periodicity. The downstream flow conditions can therefore be adjusted by the backpressure. The nozzle consists of a radial-axial section, in which spiral axisymetric flow is generated. With the adjustment of the total pressure and swirl angles in two separate distributors, a continuous variation of Mach number between 0<M<1,4 and flow angles between 12°<β<70° (from tangential) can be obtained. Further regulation of the flow quantities in the two separate distributors and boundary layer suction permits a continuous spanwise variation of the velocity and flow angle in the test section.

A Preliminary Study of Annular Diffusers With Constant Diameter Outer Walls (Suitable for Turbine Exits)

A systemmatic series of tests has been conducted on a family of annular diffusers where the outer casing is maintained at constant diameter. Such a diffuser is typical of turbine exits. Data, in the form of static pressure recovery coefficient is plotted against diffuser length for several different designs of centerbody closure. It has been shown that such diffusers can have short length centerbodies for which a set of design guides has been established.

Boundary Conditions for the Potential Equation in Transonic Internal Flow Calculation

An analysis of internal potential flow is presented showing the existence of multiple potential solutions with shocks for a given mass flow rate. These solutions are related to non isentropic Euler solutions. Inflow and outflow boundary conditions are proposed which uniquely determine the shock position allowing the calculation of potential flows which are either choked or have a supersonic inlet. Numerical computations using a multigrid finite element approach are presented and compared with exact quasi-one-dimensional Euler solutions confirming the ability of the potential method to solve accurately supersonic and choked nozzle flows.

On the Influence of the Diffuser Inlet Shape on the Performance of a Centrifugal Compressor Stage

Results from an experimental study of the influence of the diffuser inlet shape on the performance of the diffuser and the whole compressor stage are presented. The investigations were carried out using a single stage centrifugal compressor. Three different vaned diffusers were tested. From detailed flow field measurements the influence of the diffuser inlet shape on the performance of the essential components of the compressor stage, i.e. the impeller, the diffuser, and the collecting chamber was analyzed. It is shown that the reaction of the vaned diffuser on the efficiency of the impeller is only weak but the losses in the collecting chamber are considerably affected by the used diffuser types.

Theoretical and Experimental Investigation of KWU’s Most Recent HP/IP Steam Turbine Blade

A new profile has recently been developed at Kraftwerk-Union (KWU), West Germany, to increase the efficiency of todays high pressure (HP) and intermediate pressure (IP) steam turbines. The profile was described using analytical functions. Therefore, the contour could be easily modified until the surface pressure distributions, which were calculated using a singularity method, fit a desired distribution. The experiments for the aerodynamic cascade data and blade surface pressure distributions were performed at the German Aerospace Research Establishment (DFVLR), Institute for Experimental Fluid Dynamics in Goettingen. Computer codes developed at the Institute enabled additional theoretical studies. The codes used in the study included a time-marching method for calculating the 2D-flow field and an integral method for calculating the boundary layer. Both theoretical and experimental results are discussed and compared with efficiency measurements derived from a multistage testrig at KWU.

Modifications of the Ives-Liutermoza Conformal-Mapping Procedure for Turbomachinery Cascades

A conformal mapping technique, applicable to compressor and turbine cascades, is presented. The technique can be used to map the field surrounding the cascade into a rectangle, in which the image of the blade surface lies along one side of the rectangle, the image of the trailing edge is at two corners of the rectangle and the image of downstream infinity lies at the other two corners. These features make it possible to use the mapping in several contemporary flowfield-analysis codes, which carry out their calculations in such a rectangular plane. The mapping produces an O-type grid in the cascade plane.

Effect of Relative Velocity Distribution on Efficiency and Exit Flow of Centrifugal Impellers

The major problem for designing centrifugal compressors is to attain high stage efficiency as well as a wide operating range. High stage efficiency is customarily attained by the optimization of design parameters using a one-dimensional loss analysis including the relationship between the flow behavior and total pressure losses for limited types of compressors.

Low-Solidity Tandem-Cascade Diffusers for Wide-Flow-Range Centrifugal Blowers

The pressure recovery of a low-solidity circular cascade diffuser of a centrifugal blower was predicted by a simple method combining a theory of circular cascade diffusers and that of vaneless diffusers and it was compared with a series of experiments. Furthermore the stall limit of the diffuser was studied. In order to improve the performance further, a series of tandem-cascade diffusers were tested. In these diffusers, the front row of the cascade was designed for a small flow rate while the rear row of the cascade was designed for a large flow rate so that the tandem cascade would accomplish good pressure recovery in a wide range of flow rate. Experimental results showed that the operating range was as wide as that of a vaneless diffuser and the pressure recovery was excellent at a small flow rate while it was somewhat better than that in a vaneless diffuser at a large flow rate.

Three Dimensional Inviscid Computation of an Impeller Flow

The flow in a centrifugal impeller is analyzed by a quasi-three-dimensional streamline curvature method, by a three-dimensional Euler code, and by a three-dimensional finite element potential flow method. Comparison with Eckardt’s published data for a backswept impeller shows that full three-dimensional methods better predict the loading at the hub and shroud.

A Compact Diffuser System for Annular Combustors

Airflow tests have been conducted on an aerodynamic simulation of a combustor with pre-diffuser of compact configuration. The inlet Mach number throughout the tests was 0.35. The configuration was successful because of the attainment of a high pressure recovery, (Cp = 0.80), coupled with an exceptionally low total pressure loss (λ = 0.04). A useful analytical relationship is derived between the aerodynamic performance of combustor, compressor exit Mach number and diffuser performance.