APPARATUS FOR ACOUSTIC DAMPING AND OPERATIONAL CONTROL OF DAMPING, COOLING, AND EMISSIONS IN A GAS TURBINE ENGINE
Acoustic damping resonators (60, 62, 76, 78) formed in pockets (32) between reinforcing ribs (30) in a grid of ribs on the outer surface of a wall (74) surrounding a combustion gas flow path (18). Each resonator has a perforated cover plate (64A-C) spanning between sides formed by the ribs (30). Film cooling exit holes (44) are provided in the wall (74) under each resonator. Resonating chambers (48A-C) of different volumes may be provided on the wall to damp different unwanted frequencies. Different sets of resonators with different volumes may be separately controlled by respective airflow control manifolds (66) via throttle valves (68, T1-T3). Control logic (70) may control the valves based on frequency/airflow response functions (80, 82) for each size of resonator to optimize damping and cooling and to lower emissions over varying engine operating conditions.
The invention relates to an apparatus for acoustic damping of a range of acoustic frequencies, and for operational control that optimizes acoustic damping, cooling, and emission control in a combustion section of a gas turbine engine.
BACKGROUND OF THE INVENTIONGas turbine engines often use a portion of air from the compressor for cooling and emissions control. Combustion gas temperatures can approach or exceed limits for structures in the working gas flow path. Therefore, cooling of surfaces adjacent the combustion gas (“hot surface”) may be implemented. Film/effusion cooling holes are provided through walls of flow-directing structures lining the working gas flow path so that a portion of the compressed air bypasses the combustor inlets and flows through these walls. This approach is used on such structures as the combustion chamber liner, transition ducts, transition exit pieces, and other components. The holes provide film cooling and effusion cooling of these components.
In conventional gas turbines a transition duct directs a flow of combustion gas traveling at about mach 0.1 to 0.3 between each combustor and the first row of turbine blades. Compressed air in a plenum surrounding this duct has higher static pressure than the combustion gas within the transition duct. This drives compressed air from the plenum through cooling holes in the duct walls. An emerging technology for can annular gas turbine engines provides transition duct structures that direct gas from the combustor to the first row of turbine blades along a mainly tangential and partly axial flow path at proper speed and orientation to drive the first row of rotating blades without an intervening row of stationary vanes. An assembly of such transition ducts is disclosed in U.S. Pat. No. 7,721,547 to Bancalari et al. issued May 25, 2010, incorporated in its entirety herein by reference.
In the emerging technology the transition ducts accelerate the combustion gas above mach 0.3 to about mach 0.8. This increased speed provides a decrease in static pressure in the newer transition duct design, so a greater pressure difference exists between the compressed air in the plenum and the combustion gas in the duct. This, pressure difference can provide more air than is needed for film cooling. It is so great that film cooling can overshoot and separate from the hot inner surface of the duct, reducing cooling effectiveness, unless the cooling holes are kept smaller than in prior designs and smaller than is ideal. Smaller holes clog with particles more quickly.
Acoustic damping resonators have been used in gas turbine engines to damp vibrations during operation. They may be called Helmholtz resonators or High Frequency Dynamics (HFD) damping resonators. Examples are disclosed in U.S. Pat. No. 6,530,221. Each resonator includes a chamber in an enclosure welded to a wall lining the working gas flow path. They are used on structures such as a combustion chamber liners and transition ducts. The resonator enclosure may have holes that admit cooling air to purge the resonator chamber. This prevents contamination from entering the chamber from the working gas, and cools the resonator walls and flow path wall. The cooling air passes through the resonator walls, impinges on the flow path wall, and then passes through effusion/film cooling holes in the flow path wall to form a cooling film on the hot inner surface of the flow path wall. These film cooling holes also act as Helmholtz resonation ports energized by the working gas flow.
The volume of a resonator is the main determinant of its resonant frequency. Space limitations can limit the size of damping resonators, thus limiting them to damping high frequencies only, such as over 1000 Hz. But unwanted intermediate frequencies between 50-1000 Hz are generated in gas turbine engines under some conditions. Damping resonators are often needed most at areas of high heat release. This exposes their enclosure attachment welds to high temperatures via heat conduction through the flow path wall, which can be a design-limiting factor.
The invention is explained in the following description in view of the drawings that show:
This example shows a row of each type of resonator previously illustrated herein—60, 62, 76, and 78. The rows of resonators may encircle the flow directing structure or may be oriented along the working gas flow path or in any other direction. The shapes, sizes, number, arrangement, and orientation of resonators may be designed for each engine to optimize damping and rib reinforcement. The resonators do not need to be rectangular. They can be any shapes needed to fit around a flow directing structure that may be conic or irregular. Thus, the chamber shapes may include, but are not limited to, trapezoidal, triangular, hexagonal, and irregular. One or more airflow control manifolds may cover all or some of the resonators 60, 62, 76, 78. In this non-limiting example, independent throttling T1, T2, and T3 is provided by three manifolds 66 as shown in
At low engine loads, more compressed air 50 is available than is needed for combustion. If this excess air enters the combustor, it cools the combustion zone 34, increasing carbon monoxide (CO) emissions. Thus, at low engine loads, one or more of the resonator throttles 68, T1, T2, T3 may be opened, causing more compressed air 50 to bypass the combustor inlet, thus increasing combustion temperature to an optimum range, and reducing CO emissions. At higher loads including full rated power, maximum air is needed for combustion to avoid excessive temperatures in the combustion zone that increase nitrogen oxide emissions (NOx). Thus, under high loads, the resonator throttles may be closed, thus providing more compressed air to the combustion zone, which reduces its temperature to optimum range, and reducing emissions of NOx. This also maximizes damping effectiveness at high engine power when it is most needed, as exemplified by the sets of function curves in
Specific unwanted frequencies that occur at partial engine loads can be damped by minimizing the flow to certain subset(s) of resonators while not minimizing the flow to other resonators to avoid over-cooling the combustion zone. For example, for prolonged operation at ¾ load, the control logic may set throttles T1 and T2 half closed, and throttle T3 fully closed to maximize damping of a specific intermediate frequency by larger resonators 78. However, at ½ load, the control logic may fully open all throttles to minimize CO emissions, especially if ½ load is a short-term transitional stage. The apparatus herein provides a wide range of such options that can be selected by an operator and/or by predetermined control logic 70 to optimize the combination of noise reduction, emission reduction, and cooling over a wide range of operating conditions.
Some resonators may be specialized to damp specific frequencies that occur only during specific operating conditions. Under other conditions, the peak resonance (the peak of trace 80 in
One benefit of this resonator design is elimination of welds on the hot wall 74. These welds are a limiting factor in the prior design of
The attachment points of the resonator cover plates 64A, 64B, and the manifold 66 are separated by a distance (exemplified by H1 and/or H2 herein) from the hot wall by the ribs 30. The acceleration geometry 20 provides more pressure differential than is minimally needed to purge and cool the resonators 60, 62. Reducing the airflow 50 entering in the manifold 66 under some operating conditions improves engine efficiency, cooling, and damping, and reduces emissions. Reducing the pressure of the compressed air in the manifolds under all conditions allows the coolant/purge inlet and exit holes 40, 44 to be larger, thus less susceptible to particulate clogging, and causes the film cooling 52 to flow more slowly and thus adhere better to the hot inner surface of the component wall 74 without overshoot.
Separate fabrication and attachment of side walls for the resonators is not needed when reinforcing ribs 30 are already provided on the casting of the flow directing structure to oppose the pressure differential previously described. In that case, these resonators take advantage of existing pockets between the ribs of the castings of the transition piece and exit piece.
While various embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions may be made without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.
Claims
1. Apparatus for acoustic damping in a gas turbine engine, comprising:
- a combustion gas flow directing structure comprising a wall that lines a flow path for a combustion gas, the wall being surrounded by compressed air at higher pressure than a pressure of the combustion gas;
- a plurality of pockets formed by a grid of ribs on an outer surface of the wall;
- a perforated resonator plate covering one of the pockets forming a first resonator comprising a first resonating chamber having a first volume in the pocket;
- a plurality of air exit holes in the wall under the resonating chamber, the holes acting as Helmholtz resonator ports for the first resonating chamber and as film cooling holes for cooling an inner hot surface of the wall; and
- a first airflow manifold covering the first resonator and metering a first inflow of the compressed air to the first resonator.
2. The apparatus of claim 1, wherein the first inflow metering is controlled by a first throttle valve connected to a control logic that varies a position of the first throttle valve based on varying operating conditions of the engine.
3. The apparatus of claim 2, wherein the control logic controls the first throttle valve to meter the first inflow in inverse proportion to engine load, wherein the first throttle valve reduces the first inflow as an engine load increases, and increases the first inflow as the engine load decreases.
4. The apparatus of claim 1, wherein the flow directing structure comprises a flow accelerating geometry that accelerates the combustion gas in the flow path and reduces static pressure of the combustion gas in the flow path by constricting a sectional flow area of the combustion gas flow path.
5. The apparatus of claim 4, wherein the flow directing structure comprises a transition duct comprising an upstream conic portion and a downstream exit piece.
6. The apparatus of claim 1, wherein the ribs are reinforcing ribs that are cast into the flow directing structure, wherein each rib comprises a rib height above the outer surface of the wall, wherein the resonator plate is attached to the reinforcing ribs at a first height that separates the resonator plate from the outer surface of the wall, and wherein the resonator plate is not attached directly to the outer surface of the wall.
7. The apparatus of claim 6, further comprising a second resonator plate covering a second one of the pockets at a second height above the outer surface of the wall, forming a second resonator with a second resonating chamber with a different volume than the first volume.
8. The apparatus of claim 7, wherein the first airflow manifold covers both the first and second resonators, and the first inflow metering is controlled by a first throttle valve connected to a control logic that varies a position of the first throttle valve based on an operating condition of the engine;
- wherein the control logic controls the first throttle valve to meter the first inflow in inverse proportion to engine load, wherein the first throttle valve reduces the first inflow as an engine load increases, and increases the first inflow as the engine load decreases.
9. The apparatus of claim 6, further comprising:
- a second resonator formed by a second resonator plate covering a second one of the pockets, wherein the second resonator comprises a second resonating chamber having a different volume than the first volume; and
- a second airflow manifold covering the second resonator and metering a second inflow of the compressed air to the second resonator at a different flow rate than a metered flow rate of the first inflow during at least some operating conditions of the engine.
10. The apparatus of claim 9, wherein the first and second inflows are controlled by respective first and second throttle valves connected to a control logic that varies a position of the each throttle valve based on an operating condition of the engine.
11. The apparatus of claim 9 wherein the first and second resonating chambers have the same height above the outer surface of the wall.
12. Apparatus for acoustic damping in a gas turbine engine, comprising:
- a wall surrounding a flow path for a combustion gas;
- a plenum for compressed air around an outer surface of the wall;
- a first and second plurality of acoustic damping resonators on the outer surface of the wall, the resonators of the first plurality each comprising a resonating chamber with a first volume, and the resonators of the second plurality each comprising a resonating chamber with a second volume that is different from the first volume;
- film cooling exit holes in the wall under each chamber;
- a first airflow control manifold that meters a first inflow of the compressed air to the first plurality of acoustic damping resonators; and
- a second airflow control manifold that meters a second inflow of the compressed air to the second plurality of acoustic damping resonators;
- wherein the first and second manifolds meter the first and second inflows by different amounts from each other during at least some operating conditions of the engine, and both manifolds reduce a pressure of the compressed air provided to the resonators compared to a pressure of the compressed air in the plenum.
13. The apparatus of claim 12, wherein at least some of the first resonating chambers have the same height as at least some of the second resonating chambers.
14. The apparatus of claim 12, wherein the first and second airflow control manifolds comprise respective first and second throttle valves that meter the respective first and second inflows, wherein the throttle valves are connected to a control logic that controls the throttle valves to vary each of the first and second inflows based on a set of damping frequency/airflow response curves of the resonators to optimize acoustic damping, cooling, and combustion temperature in the engine under varying operating conditions of the engine.
15. The apparatus of claim 12, wherein the wall comprises a flow accelerating geometry that accelerates the combustion gas in the flow path to more than mach 0.3, and reduces the static pressure of the combustion gas in the flow path by constricting a sectional flow area of the combustion gas flow path; wherein the resonating chambers are formed in pockets between reinforcing ribs cast on the outer surface thereof.
16. The apparatus of claim 12, further comprising a third plurality of acoustic damping resonators on the outer surface of the wall, each resonator of the third plurality comprising a resonating chamber of different volume than the chamber volumes of the first and second pluralities; wherein the first second and third pluralities of damping resonators in combination damp at least some frequencies over range of 300-4000 Hz.
17. The apparatus of claim 12, wherein the first and second inflows are metered by respective valves controlled by control logic that controls acoustic damping of a range of acoustic frequencies both above and below 1000 Hz, and controls a combination of acoustic damping, cooling, and emission control in a combustion section of the gas turbine engine over a range of operating conditions.
18. The apparatus of claim 12, wherein the respective inflows of the compressed air to the first and second pluralities of resonators are variably metered by respective first and second throttles to control CO and NOx emissions and to control damping of frequencies both above and below 1000 Hz over a range of engine operating conditions under control of a control logic based on a set of frequency/airflow response functions for each of the first and second pluralities of resonators.
Type: Application
Filed: Sep 26, 2013
Publication Date: Mar 26, 2015
Inventor: Reinhard Schilp (Orlando, FL)
Application Number: 14/037,445
International Classification: F23R 3/16 (20060101);