Patent Application
20070224047
This invention relates to a multi-piece hollow impeller and a method of manufacturing and using the same. The impeller is suitable for use in a radial flow centrifugal compressor, for example, or other rotary machines.
Small gas turbine compressors often use a radial compressor impeller as a last stage to boost air pressure. The radial compressor impeller includes a metal wheel with curved blades that accelerate the flow of air from an inlet near the inner diameter of the impeller to an exit near the outer diameter of the impeller. The impeller includes a single bore, or support structure, that carries the centrifugal loads on the impeller. The single radial impeller stage provides a pressure rise equivalent to the pressure ratio that several axial compressor stages can provide but with fewer parts. The single stage impeller also serves to reduce compressor axial length relative to axial compressor stages at an equivalent pressure rise.
Current impellers typically have an asymmetric solid, radar dish-shaped bore that tends to roll and deflect axially when under high centrifugal loads. In particular, conventional impellers axially deflect at the impeller tip in generally the opposite direction as airflow into the impeller inlet. The deflection is caused by centrifugal inertial loads on the asymmetric impeller and by temperature gradients in the impeller. As a result, the compressor must be designed with clearances to accommodate the deflection of the impeller tip throughout its entire operating range. The compressor is designed such that a desired clearance is obtained at a particular operating condition of the compressor, which results in less than desired performance during off design point operation reducing the overall efficiency of the compressor.
What is needed is an impeller that provides improved axial tip clearance throughout the entire operating range of the compressor.
The present invention provides an impeller for use in, for example, a compressor. The impeller is arranged within a housing that includes a shroud. The impeller is rotatable about an axis and includes first and second impeller portions that are secured to one another. The first impeller portion supports multiple blades that are arranged adjacent to the shroud. An impeller outlet and inlet are provided by the blades, and the impeller inlet is arranged radially inwardly from the impeller outlet. An interior cavity is formed between the first and second portions. The first and second impeller portions respectively include first and second surfaces that are secured to one another near a tip of the impeller, for example, by using a bonding material.
In an example embodiment, inlet and outlet holes are provided on the impeller and arranged in communication with the inner cavity to provide a cooling flow there through. In an example embodiment, a circumferential gap is arranged between the first and second impeller portions to permit relative axial movement between them during centrifugal loading of the impeller.
In one example, the impeller is manufactured by forging the first and second impeller portions. The first and second impeller portions are secured to one another using a bonding material arranged near the tip of the impeller by a transient liquid phase process, for example. The interior cavity is shaped for desired cooling and loading of the first and second impeller portions.
The inventive impeller provides improved dimensional stability of the impeller to reduce the running clearance needed between the impeller and housing throughout the operating range of the compressor.
The inventive impeller provides improved tip alignment between the impeller outlet and the diffuser inlet throughout the operating range of the compressor.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.
A compressor 10 that provides a housing 12 is shown in
The impeller 18 includes support surfaces 26 for rotationally supporting the impeller 18. A cylindrical surface 27 is arranged between the support surfaces 26, in the example shown. A bore 28 extends outwardly away from the cylindrical surface 27. The bore 28 is the structural portion of the impeller 18 that must withstand centrifugal loads and temperature gradients to maintain the dimensional stability of the impeller 18 throughout its operating range. In the prior art, the bore is a solid structure that supports the impeller blades in such a manner that an asymmetrical, radar dish-shaped impeller is provided.
The inventive impeller 18 is provided using multiple pieces. In the example shown, first and second impeller portions 30 and 32 are secured to one another to provide an interior cavity 34. As shown in
The first and second impeller portions 30 and 32 respectively include first and second surfaces 40 and 42 (
The interior cavity 34 can also be used to cool the impeller 18 to avoid distortion of the impeller 18 due to temperature gradients in the impeller. In one example, multiple outlet apertures 36 are provided on the cylindrical surface 27, as shown in
The first and second impeller portions 30 and 32 respectively include first and second contoured surfaces 44 and 46 that define the interior cavity 34. In the example shown, the first and second contoured surface 44 and 46 are generally mirror images of one another about an axial plane to minimize distortion of the impeller 18 due to centrifugal loading. The shape of the first and second contoured surfaces 44 and 46 can also be selected to achieve desired cooling and load distribution of the impeller 18.
The first and second impeller portions 30 and 32 tend to move axially toward one another under centrifugal loading. A circumferential gap 48 is provided between the first and second impeller portions 30 and 32 in the area of the cylindrical surface 27, as shown in
Although several preferred embodiments of this invention have been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.
