Impellers are widely used in a variety of applications to compress a fluid. For example, impellers are often used in air compressor applications for use in generating compressed air to power pneumatic tools and the like. Alternatively, impellers are used to compress a fluid for use in a pressurized system such as in supplying a pressurized fluid stream for use on a fire truck or pumping station. Further yet, such impellers are commonly used in the design and operation of aircraft engines, whereby a compressed fluid stream is provided via an impeller to propel an airplane in a desired direction. In any of the foregoing applications, it is desirable to provide an impeller capable of operating under varying flow conditions to provide a continuous supply of pressurized fluid, regardless of external forces.
As can be appreciated from the foregoing discussion, impellers are operable to compress a fluid stream for use in a plurality of applications. As previously discussed, one such application is an air compressor. Conventional compressors typically include an impeller, a diffuser, and a volute, whereby the diffuser is in fluid communication with both the impeller and the volute and is operable to transfer a compressed air stream from the impeller to the volute for use in an external system. The impeller commonly includes a plurality of blades that are operable to receive and compress an external air stream between a hub of the impeller and a stationary shroud. Specifically, the impeller captures the external air stream at an inducer disposed proximate to a leading edge of each blade such that the captured mass air flow is forced between the hub and the stationary shroud through rotation of the impeller. The inducer is generally operable to capture the external air stream and force it between the hub and the stationary shroud as the impeller is rotated due to the generally curved or arcuate shape of the leading edge of each blade.
As can be appreciated, as the air stream travels between each of the blades, the shape of the shroud and hub are such that the air stream is compressed prior to reaching the volute. The compressed air stream is received into the diffuser for distribution to the volute prior to being used by an external application such as a pneumatic tool or a vehicle engine or a fuel cell. The diffuser commonly includes a plurality of stationary vanes which are operable to diffuse the air stream from the impeller in an effort to increase the static pressure of the compressed air. Such increases in static pressure generally increase the pressure of the air stream, thereby providing a desired output of pressurized air from the compressor.
In compressor design, it is increasingly important to deliver a constant stream of pressurized air to ensure proper operation of an external device. As can be appreciated, interruption of a compressor can cause external devices, such as pneumatic tools, to seize and abruptly stop working. A common occurrence of such compressor failure is impeller blade fracture or blade cracking due to stresses imparted on the impeller blades through compression of an air stream. Such blade facture or cracking impedes the performance of the impeller as the requisite pressurized air cannot be delivered without first replacing the fractured or cracked impeller blade. Conventional air compressors commonly include an impeller disposed within a sealed housing such that replacement and repair of the impeller commonly requires a significant amount of time and accompanying expense when blade fracture or cracking occurs. As can be appreciated, such repairs can be costly both from the standpoint of requiring a replacement impeller and also from the standpoint that the compressor is unusable until the requisite repairs can be completed.
To obviate the need for impeller repair, conventional impeller designs have commonly incorporated impeller blades having an increased thickness to stave off blade cracking and fracture. In most cases, such increases in blade thickness come with an aerodynamic penalty. More particularly, by increasing the thickness of each blade in an effort to improve strength characteristics and limit blade fracture and cracking, aerodynamic performance of the blade is sacrificed as thinner blade profiles typically provide for improved aerodynamic performance and efficiency. In this manner, conventional impellers, and impeller blades, suffer from the disadvantage of sacrificing aerodynamic performance to meet requisite strength characteristics.
Therefore, an impeller incorporating an airfoil or blade which provides adequate structural support while concurrently providing optimum aerodynamic performance of each airfoil or blade is desirable in the industry.