WO2015048230A1

WO2015048230A1 - Vortex generator on a compressor blade of a turbocharger

Info

Publication number: WO2015048230A1
Application number: PCT/US2014/057368
Authority: WO
Inventors: Stephanie DEXTRAZE
Original assignee: Borgwarner Inc.
Priority date: 2013-09-30
Filing date: 2014-09-25
Publication date: 2015-04-02

Abstract

A vortex generator (40) on the suction side (30) of a blade (20) of a compressor impeller (14) of a turbocharger to delay the onset of surge. Delayed airflow separation from the blade (20) delays the onset of surge, allowing the compressor to have a wider range of operating conditions.

Description

VORTEX GENERATOR ON A COMPRESSOR BLADE OF A TURBOCHARGER

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and all the benefits of U.S. Provisional Application No. 61/884,258, filed on September 30, 2013, and entitled "Vortex Generator On A Compressor Blade Of A Turbocharger," which is incorporated herein by reference.

BACKGROUND

1. Field of the Disclosure

This disclosure relates to a component for turbochargers. More particularly, this disclosure relates to a vortex generator on the suction side of a compressor blade.

2. Description of Related Art

Advantages of turbocharging include increased power output, lower fuel consumption and reduced pollutant emissions. The turbocharging of engines is no longer primarily seen from a high power performance perspective, but is rather viewed as a means of reducing fuel consumption and environmental pollution on account of lower carbon dioxide (CO2) emissions. Currently, a primary reason for turbocharging is using the exhaust gas energy to reduce fuel consumption and emissions. In turbocharged engines, combustion air is pre- compressed before being supplied to the engine. The engine aspirates the same volume of air- fuel mixture as a naturally aspirated engine, but due to the higher pressure, thus higher density, more air and fuel mass is supplied into a combustion chamber. Consequently, more fuel can be burned, so that the engine's power output increases relative to the speed and swept volume.

In exhaust gas turbocharging, some of the exhaust gas energy, which would normally be wasted, is used to drive a turbine. The turbocharger returns some of this normally wasted exhaust energy back into the engine, contributing to the engine's efficiency and saving fuel. A compressor, which is mounted on the same shaft as the turbine, draws in filtered ambient air, compresses it, and then supplies it to the engine.

A turbocharger is a type of forced induction system used with internal combustion engines. Turbochargers deliver compressed air to an engine intake, allowing more fuel to be combusted, thus boosting an engine's horsepower without significantly increasing engine weight. Thus, turbochargers permit the use of smaller engines that develop the same amount of horsepower as larger, naturally aspirated engines. Using a smaller engine in a vehicle has the desired effect of decreasing the mass of the vehicle and enhancing fuel economy. Moreover, the use of turbochargers permits more complete combustion of the fuel delivered to the engine, which contributes to the highly desirable goal of a cleaner environment. Turbochargers typically include a turbine housing connected to the engine's exhaust manifold, a compressor housing connected to the engine's intake manifold, and a center bearing housing coupling the turbine and compressor housings together. A turbine wheel in the turbine housing is rotatably driven by an inflow of exhaust gas supplied from the exhaust manifold. A shaft rotatably supported in the center bearing housing connects the turbine wheel to a compressor impeller in the compressor housing so that rotation of the turbine wheel causes rotation of the compressor impeller. The shaft connecting the turbine wheel and the compressor impeller defines an axis of rotation.

This disclosure focuses on the blades of a compressor impeller of a turbocharger. The compressor is designed to help increase the intake manifold pressure and density to allow the engine cylinders to ingest a greater mass of air during each intake stroke. A compressor impeller typically has curved blades for non-axial flow.

The performance of the compressor is shown on a chart commonly called a "map." The compressor performance map defines, based on inlet conditions, the usable operating characteristics of the compressor in terms of airflow and pressure ratio. The compressor RPM lines show, for a stated compressor speed, the pressure ratio delivered as a function of airflow.

A line extending up the left side of the compressor performance map is referred to as a surge line. It defines, for each pressure ratio, the minimum airflow at which the compressor can operate with sufficient air system stability. The surge line indicates when there is a full system reversal of flow. Local stall conditions can occur to the right of the surge line and may propagate to other locations along the compressor blade.

It is desirable therefore to provide a turbocharger compressor blade that can improve the surge margin and widen the compressor performance map so that at a given pressure ratio and/or a given compressor impeller speed, a larger spread of airflow values are available between a surge line and a choke line of the compressor performance map. SUMMARY

The disclosure provides for a compressor blade of a turbocharger that improves surge margin, i.e., a surge line on a compressor performance map is moved to the left, by having vortex generators on the suction side of the compressor blade that delay the onset of surge. Various vortex generators can be located on the suction side of a compressor blade of the turbocharger, where separation occurs, to delay the onset of surge and to provide a wider compressor performance map.

The concept of the vortex generator is to put them just before separation would be about to occur on an airfoil surface. Vortex generators, such as wedges, will re-energize the boundary, thus either delaying the onset of separation or optimally removing it all together. Separation is a performance inhibitor because it causes aerodynamic losses, and it also leads to surge.

In turbochargers, surge occurs when airflow is low causing the flow on the compressor blade suction side to separate, which is known as stall. Eventually, this phenomenon causes the flow direction to reverse on the compressor blade, causing instability and premature failure of the compressor. Surge is a critical limitation for the operation of the compressor, and operating points must be kept within certain margins from surge in order to not significantly limit the overall operation of the turbocharger.

To suppress flow separation on the suction side of the compressor blade, which causes surge, vortex generators can be cast or machined within the suction side wall of the blade itself. Vortex generators on the suction side of the compressor blade energize the boundary layer with low airflow, and therefore it takes a longer time and a higher pressure ratio to cause separation of flow on the blade. Thus, the compressor can run at lower airflows without separation and thus without surge. Delayed separation of flow on the compressor blades delays the onset of surge, allowing the compressor to have a wider range of operating conditions.

The vortex generators extending upright from the suction side wall of the blade may be v- shaped, in one or more combined raised elements.

BRIEF DESCRIPTION OF THE DRAWINGS Advantages of the present disclosure will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

Figure 1 is a perspective view of a compressor impeller with curved blades;

Figure 2 is a partial view of a compressor impeller with vortex generators on the suction side of blades;

Figure 3 is a cross-sectional view of a vortex generator; and

Figure 4 is a plain view of a preferred chevron arrangement for a vortex generator on a blade.

DETAILED DESCRIPTION OF THE EMBODIMENTS

A turbocharger is generally known with a compressor housing including a compressor impeller 14. The compressor impeller 14 is mounted on one end of a shaft 18 and is housed within the compressor housing. A rotating shaft 18 is driven by a turbine wheel such that rotation of the turbine wheel causes rotation of the compressor impeller 14.

As known in the art, the turbine wheel is rotatably driven by an inflow of exhaust gas supplied from an exhaust manifold, which rotates the shaft 18, thereby causing the compressor impeller 14 to rotate. As the compressor impeller 14 rotates, air is drawn in and is compressed to be delivered at an elevated pressure to an intake manifold of an engine. In other words, the turbine wheel rotatably drives the compressor impeller 14.

A typical compressor impeller 14 includes a series of curved blades 20 that may include full length blades 22 and partial blades 24 to maximize functional blade surfaces around the compressor impeller 14. The blades 20 include a suction side 30, as specifically shown as 32 full length blades 22 and as 34 on partial blades 24. Ideally, flow separation is delayed or reduced to lessen stalling, which improves effectiveness.

A vortex generator 40 is a raised element 42 or series of raised elements 44 and 46 that inhibit boundary layer separation and thereby reduce drag with a vortex having rotary motion to the airflow. Vortex generators 40 can be cast or machined within a suction side 30 of a blade 20, primarily depending on how the compressor impeller 14 is made. The specific geometry of the vortex generator 40 causes instability to the airflow, including rotary motion and turbulence. A long upright bump could function as a vortex generator, but it is typically preferred to add the least amount of material possible to the blade 20. Thus, raised elements 44 and 46 that are intermittent are preferred. The raised elements 44 and 46 forming a vortex generator 40 are shown in Figure

2 toward the tail of the full length blades 22 and on a center portion of the partial blades 24. Based on the flow separation without vortex generators, these locations improve effectiveness with vortexes that tend to keep airflow adjacent to the blades 20.

In Figure 3, the cross section of a vortex generator 40 shows minimal corners to reduce stress and unnecessary drag while still delaying flow separation from the blade 20 and aerodynamic stalling to improve effectiveness. While many types of bumps could create a vortex, trapezoidal or v-shaped vortex generators may be preferred. A chevron shaped arrangement with two raised elements 44 and 46 form a preferred vortex generator 40 as shown in Figure 4. Ideally, the vortex generator 40 may not have a sharp edge as a manufacturing preference, but sharp edges may be preferably from an aerodynamic perspective. But a vortex generator 40 may have rounded edges.

Vortex generators 40 on the suction side 30 of a blade 20 delay the onset of surge to provide a wider compressor performance map. With regard to a compressor performance map, keeping airflow attached to the blade 20 moves the surge line to the left for a wider compressor performance map.

While the preferred concept of vortex generators 40 on the suction side 30 of a blade 20 for a compressor is disclosed, vortex generators could also be used on a turbine wheel.

The invention has been described in an illustrative manner, and it is to be understood that the terminology used is intended to be in the nature of words of description rather than limitation. Many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced other than as specifically enumerated within the description.

Claims

What is claimed:

1. A turbocharger having a compressor impeller (14) and a turbine wheel connected by a rotating shaft (18), the compressor impeller (14) comprising a plurality of blades (20), at least one blade (20) having a vortex generator (40) on the suction side (30) of the blade (20).

2. The turbocharger of claim 1 wherein surge margin is improved by reducing airflow separation from the blade (20) of the compressor impeller (14).

3. The turbocharger of claim 1 wherein the vortex generator (40) extend upright from the suction side (30) in a v-shape.

4. The turbocharger of claim 1 wherein the plurality of blades (20) include full length blades (22) each with suction side (32) and partial blades (24) each with suction side (34).

5. The turbocharger of claim 4 wherein the vortex generator (40) includes a series of intermittent raised elements (44 and 46) on each suction side (32, 34) that inhibit boundary layer separation.

6. The turbocharger of claim 5 wherein the raised elements (44 and 46) are toward a tail of the full length blades (22) and on a center portion of the partial blades (24).

7. The turbocharger of claim 1 wherein the vortex generator (40) has rounded edges.

8. The turbocharger of claim 1 wherein the vortex generator (40) is in a chevron shaped arrangement with two raised elements (44 and 46).

9. A turbocharger having a compressor impeller (14) and a turbine wheel connected by a rotating shaft (18), the compressor impeller (14) comprising a plurality of curved blades

(20), each having a vortex generator (40) extending from the suction side (30) of the curved blade (20) at a place just before where separation would otherwise occur without the vortex generator (40), the vortex generator (40) includes a series of intermittent raised elements (44 and 46).

10. The turbocharger of claim 9 wherein the plurality of blades (20) include full length blades (22) each with suction side (32) and partial blades (24) each with suction side (34) wherein the raised elements (44 and 46) are on each suction side (32) toward a tail of the full length blades (22) and on each suction side (34) at a center portion of the partial blades (24).