Patent Application
20140341727
The present disclosure relates to centrifugal compressors used for compressing a fluid such as air, and more particularly relates to centrifugal compressors and methods in which surge of the compressor is controlled by bleeding off a portion of the at least partially compressed fluid and recirculating the portion to the inlet of the compressor.
Centrifugal compressors are used in a variety of applications for compressing fluids. A single-stage centrifugal compressor can achieve peak pressure ratios above 4.0 and is much more compact in size than an axial flow compressor of equivalent pressure ratio. Accordingly, centrifugal compressors are commonly used in turbochargers for boosting the performance of gasoline and diesel engines for vehicles.
In turbocharger applications, it is important for the compressor to have a wide operating envelope, as measured between the “choke line” at which the mass flow rate through the compressor reaches a maximum possible value because of sonic flow conditions in the compressor blade passages, and the “surge line” at which the compressor begins to surge. Compressor surge is a compression system instability associated with flow oscillations through the whole compressor system. It is usually initiated by aerodynamic stall or flow separation in one or more of the compressor components as a result of exceeding the limiting flow incidence angle to the compressor blades or exceeding the limiting flow passage loading.
Surge causes a significant loss in performance and thus is highly undesirable. In some cases, compressor surge can also result in damage to the engine or its intake pipe system.
Thus, there exists a need for an improved apparatus and method for providing compressed fluid, such as in a turbocharger, while reducing the occurrence of compressor surge. In some cases, the prevention of compressor surge can expand the useful operating range of the compressor.
The present disclosure is directed to a centrifugal compressor having a fluid recirculation system aimed at controlling surge. In accordance with one embodiment disclosed herein, a centrifugal compressor for a turbocharger for compressing air to be delivered to an engine air intake comprises a compressor wheel having a hub defining a rotational axis and having a plurality of circumferentially spaced blades each joined to the hub and extending generally radially outwardly to a blade tip, each of the blades having a leading edge and a trailing edge spaced downstream from the leading edge along a flow direction of a main flow of air through the wheel. The compressor includes a compressor housing in which the compressor wheel is mounted so as to be rotatable about the rotational axis of the compressor wheel, the compressor housing including an inlet duct through which air enters in a direction generally parallel to the rotational axis of the compressor wheel and is led by the inlet duct into the compressor wheel. A wheel shroud is defined by the compressor housing. The wheel shroud is located radially adjacent the blade tips and extends upstream from the blades with respect to the main flow proceeding along the flow direction, and terminates at a leading edge of the wheel shroud spaced axially upstream of the blade leading edges. The wheel shroud has a radially inner surface wetted by the main flow and has a radially outer surface spaced radially inward of an inner surface of the inlet duct, such that an annular space is defined between the radially outer surface of the wheel shroud and the inner surface of the inlet duct;
The wheel shroud proximate the blade tips defines a port that extends generally radially outwardly from the radially inner surface to the radially outer surface of the wheel shroud, into the annular space. A plurality of circumferentially spaced slots are formed in the wheel shroud, each slot extending through the leading edge of the wheel shroud such that the slot is open at the leading edge of the wheel shroud. The slots extend axially downstream to a position axially spaced upstream from the port in the wheel shroud. Each slot over an entire length thereof extends from the radially inner surface to the radially outer surface of the wheel shroud. Accordingly, a portion of air passing through the compressor wheel can flow out through the port into the annular space, then upstream within the annular space, and finally inwardly through the slots so as to be injected, as recirculated air, back into the main flow.
In certain embodiments, each of the shroud portions that extend circumferentially between each slot and a neighboring slot, at the radially outer surface of the wheel shroud, has a greater circumferential extent than does each of the slots. In other words, the slots are relatively narrow in the circumferential direction.
In some embodiments as described herein, the slots are angled with respect to a radial direction, in an opposite sense relative to a rotation direction of the compressor wheel, such that the recirculated air is injected back into the main flow with a counter-swirl. Alternatively, the slots can be oriented substantially radially so as to inject the recirculated air into the main flow with substantially no swirl component. Still another alternative is to angle the slots in the same sense as the rotation direction of the compressor wheel, thereby imparting pre-swirl to the injected fluid.
In other embodiments, the compressor also includes an annular flow-guiding member that extends from the inlet duct radially inwardly and axially downstream to a trailing edge of the flow-guiding member. This trailing edge is proximate the leading edge of the wheel shroud. The flow-guiding member serves to substantially prevent the main flow of air from passing through the slots while allowing the recirculated air to pass through the slots. The trailing edge of the flow-guiding member can be axially spaced from the leading edge of the wheel shroud, such that there is a 360° gap between the trailing edge of the flow-guiding member and the leading edge of the wheel shroud.
In some embodiments, there are at least eight of the slots, distributed over 360° about the wheel shroud.
Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:
The present invention now will be described more fully hereinafter with reference to the accompanying drawings in which some but not all embodiments of the inventions are shown. Indeed, these inventions may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout.
A turbocharger 10 in accordance with one embodiment of the invention is depicted in
With particular reference to
The bleed port 42 is connected to a passage 44 defined in the compressor housing 22. More specifically, the passage 44 is defined between a radially outer surface of the wheel shroud 28 and a radially inner surface of the duct wall 26. In one embodiment, the passage 44 comprises a substantially uninterrupted full 360° annular passage, except for the presence of a relatively small number of support struts 27 that extend between the duct wall 26 and the wheel shroud 28 as further described below. The passage 44 extends in a generally axial direction opposite to the direction of the main fluid flow in the inlet duct 24, to a point spaced upstream (with respect to the main fluid flow) of the compressor blade leading edges.
The wheel shroud 28 extends upstream from the blades 16 with respect to the main flow proceeding along the flow direction and terminates at a leading edge 29 of the wheel shroud spaced axially upstream of the blade leading edges 30. The wheel shroud defines a plurality of circumferentially spaced slots 50 in the wheel shroud, forming part of the recirculation system 40. Each slot extends through the leading edge 29 of the wheel shroud such that the slot is open at the leading edge of the wheel shroud, and extends axially downstream to a position axially spaced from the port 42 in the wheel shroud. Each slot over its entire length extends from the radially inner surface to the radially outer surface of the wheel shroud 28. The wheel shroud defines a shroud portion extending circumferentially between each slot and a neighboring slot. Each shroud portion, at the radially outer surface of the wheel shroud, can have a greater circumferential extent than each slot.
A portion of the air passing through the compressor wheel 12 can flow out through the port 42 into the annular space 44, then upstream within the annular space, and finally inwardly through the slots 50 so as to be injected, as recirculated air, back into the main flow approaching the compressor wheel. This recirculation of air serves to help control surge of the compressor.
The slots 50 in some embodiments are angled with respect to a radial direction, in an opposite sense relative to a rotation direction of the compressor wheel 12, such that the recirculated air is injected back into the main flow with a counter-swirl. Thus, in
The number of the slots 50 can vary depending on the particular application. In some embodiments, there are at least eight slots. The spacing of the slots circumferentially can be uniform or asymmetric (non-uniform). Asymmetrically spaced slots can be used to overcome the non-uniform flow condition at the port 42 caused by the housing 22, and thereby make the flow bleeding system 40 more effective.
In the embodiment of
In other embodiments, such as the one depicted in
Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.
