Patent Publication Number: US-2012033904-A1

Title: Hydrodynamic gas film bearing cooling flow control system

Description:
TECHNICAL FIELD 
     The present invention generally relates to hydrodynamic gas film bearings, and more particularly relates to a system for adaptively controlling cooling flow to hydrodynamic gas film bearings. 
     BACKGROUND 
     Hydrodynamic gas film bearings may be used in various high-speed rotating machines. A hydrodynamic gas film bearing runs on a film of gas, which allows it to operate without oil. During operation, a hydrodynamic gas film bearing generates heat. To remove the generated heat, a flow of cooling gas is supplied to the hydrodynamic gas film bearing. The cooling gas flows into the hydrodynamic gas film bearing, absorbs the heat, and exits the hydrodynamic gas film bearing carrying away the heat. As may be appreciated, the cooling gas supply system is preferably designed to provide sufficient cooling gas to maintain metal temperatures within acceptable limits. 
     Cooling gas requirements for hydrodynamic gas film bearings can vary significantly with bearing load, with the rotational speed of the component that the hydrodynamic gas film bearing mounts, and with the pressure and temperature of the cooling gas. A typical cooling gas system for hydrodynamic gas film bearings is unregulated, meaning that it does not controllably adjust the flow of cooling for varying conditions. The cooling gas system is designed so that it meets the cooling requirements for the most limiting condition, but then flows more cooling gas than is required at all other design points. If the difference between the most limiting condition and the typical operating condition is large the excess cooling gas can have a noticeable effect on the efficiency of the device. In the context of a gas turbine engine environment, the cooling gas source is typically the compressor. Hence, oversupplying a hydrodynamic gas film bearing with cooling gas may increase overall engine fuel consumption. 
     Accordingly, it is desirable to provide a system that will control the flow of cooling gas to one or more hydrodynamic gas film bearings, and thus not oversupply the hydrodynamic gas film bearings with cooling gas. The present invention addresses at least this need. 
     BRIEF SUMMARY 
     In one embodiment, and by way of example only, a hydrodynamic gas film bearing cooling gas control system includes a hydrodynamic gas film bearing, a supply conduit, and a flow control device. The supply conduit is in fluid communication with the hydrodynamic gas film bearing, is coupled to receive a flow of cooling gas from a cooling gas supply source, and is configured to supply the flow of cooling gas to the hydrodynamic gas film bearing. The flow control device is coupled to the supply conduit and is responsive to a physical characteristic of the cooling gas or ambient environment to move between at least two positions to thereby vary the flow of cooling gas, through the supply conduit, to the hydrodynamic gas film bearing. When the physical characteristic of the cooling gas is pressure, restriction of the flow of cooling gas is varied at least inversely with the cooling gas pressure. 
     In another exemplary embodiment, a hydrodynamic gas film bearing cooling gas control system includes a hydrodynamic gas film bearing, a first supply conduit, a first flow control device, a second supply conduit, and a second flow control device. The first supply conduit is in fluid communication with the hydrodynamic gas film bearing, is coupled to receive a flow of cooling gas from a cooling gas supply source, and is configured to supply the flow of cooling gas to the hydrodynamic gas film bearing. The first flow control device is coupled to the first supply conduit and is responsive to a physical characteristic of the cooling gas or ambient environment to move between at least two positions to thereby vary the flow of cooling gas, through the first supply conduit, to the hydrodynamic gas film bearing. The second supply conduit is in fluid communication with the hydrodynamic gas film bearing, is coupled to receive a flow of cooling gas from the cooling gas supply source, and is configured to supply the flow of cooling gas to the hydrodynamic gas film bearing. The second flow control device is coupled to the second supply conduit and is responsive to the physical characteristic of the cooling gas or ambient environment to move between at least two positions to thereby vary the flow of cooling gas, through the second supply conduit, to the hydrodynamic gas film bearing. 
     In still another exemplary embodiment, a hydrodynamic gas film bearing cooling gas control system includes a hydrodynamic gas film bearing, a supply conduit, a first flow control device, and a second flow control device. The supply conduit is in fluid communication with the hydrodynamic gas film bearing, is coupled to receive a flow of cooling gas from a cooling gas supply source, and is configured to supply the flow of cooling gas to the hydrodynamic gas film bearing. The first flow control device is coupled to the supply conduit and is responsive to a physical characteristic of the cooling gas or ambient environment to move between at least two positions to thereby vary the flow of cooling gas, through the supply conduit, to the hydrodynamic gas film bearing. The second flow control device is coupled to the supply conduit and is responsive to the physical characteristic of the cooling gas or ambient environment to move between at least two positions to thereby vary the flow of cooling gas, through the supply conduit, to the hydrodynamic gas film bearing. 
     In yet another exemplary embodiment, a hydrodynamic gas film bearing cooling gas control system includes a hydrodynamic gas film bearing, a supply conduit, a flow control device, a first flow restriction, and a second flow restriction. The supply conduit is in fluid communication with the hydrodynamic gas film bearing, is coupled to receive a flow of cooling gas from a cooling gas supply source, and is configured to supply the flow of cooling gas to the hydrodynamic gas film bearing. The flow control device is coupled to the supply conduit and responsive to a physical characteristic of the cooling gas or ambient environment to move between a first position and a second position. The first flow restriction is disposed between the flow control device and the supply conduit, and has a first cross sectional flow area. The second flow restriction is disposed between the flow control device and the supply conduit, and has a second cross sectional flow area that is greater than the first cross sectional flow area. The cooling gas flows through the first flow restriction when the flow control device is in the first position, and through the second flow restriction when the flow control device is in the second position. 
     Furthermore, other desirable features and characteristics of the hydrodynamic gas film bearing cooling gas control system will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and 
         FIG. 1  depicts a simplified schematic of an exemplary embodiment of gas turbine engine; 
         FIGS. 2-5  depict simplified schematic representations of various embodiments of a hydrodynamic gas film bearing cooling gas supply system that may be implemented in a machine, such as the gas turbine engine of  FIG. 1 , that includes one or more hydrodynamic gas film bearings; and 
         FIGS. 6-8  depict simplified schematics of exemplary alternative configurations of hydrodynamic gas film bearing cooling gas supply systems. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. As used herein, the word “exemplary” means “serving as an example, instance, or illustration.” Thus, any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments. All of the embodiments described herein are exemplary embodiments provided to enable persons skilled in the art to make or use the invention and not to limit the scope of the invention which is defined by the claims. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary, or the following detailed description. Thus, although the description is explicitly directed toward an embodiment that is implemented in a gas turbine engine, it should be appreciated that it can be implemented in various other types of rotating machines that may be known now or developed hereafter in the art. 
     Turning now to  FIG. 1 , an embodiment of an exemplary gas turbine engine  100  is shown in simplified schematic form. The gas turbine engine  100  includes a compressor  102 , a combustor  104 , and a turbine  106 , all preferably housed within an engine housing  108 . During operation of the gas turbine engine  100 , the compressor  102  draws ambient air into a compressor inlet  101 , via a housing inlet duct  103  formed in the engine housing  108 . The compressor  102  compresses the ambient air, and supplies a portion of the compressed air to the combustor  104 , and may also supply compressed air to a bleed air port  105 . The bleed air port  105 , if included, may be used to supply compressed air to, for example, a non-illustrated environmental control system or other load. It will be appreciated that the compressor  102  may be any one of numerous types of compressors now known or developed in the future. For example, the compressor may be a single-stage or a multi-stage centrifugal compressor. 
     The combustor  104  receives the compressed air from the compressor  102 , and also receives a flow of fuel from a non-illustrated fuel source. The fuel and compressed air are mixed within the combustor  104 , and are ignited to produce relatively high-energy combustion gas. The combustor  104  may be implemented as any one of numerous types of combustors now known or developed in the future. Non-limiting examples of presently known combustors include various can-type combustors, various reverse-flow combustors, various through-flow combustors, and various slinger combustors. 
     No matter the particular type of combustor  104  that is used, the relatively high-energy combustion gas that is generated in the combustor  104  is supplied to the turbine  106 . As the high-energy combustion gas expands through the turbine  106 , it impinges on the turbine blades (not shown in  FIG. 1 ), which causes the turbine  106  to rotate. It will be appreciated that the turbine  106  may be implemented using any one of numerous types of turbines now known or developed in the future including, for example, a vaned radial turbine, a vaneless radial turbine, and a vaned axial turbine. No matter the particular type of turbine that is used, the turbine  106  is mounted on a shaft  112 , which is coupled to and drives the compressor  102 . Moreover, depending on the particular end-use of the gas turbine engine  100 , the turbine  106 , via the shaft  112 , may also be coupled to and drive a non-illustrated generator, a non-illustrated propeller, and/or one or more numerous other non-illustrated components. 
     The shaft  112  is rotationally mounted within the engine housing  108  via a plurality of bearings  114 . In the depicted embodiment, only two bearings are depicted, a forward bearing  114 - 1  and an aft bearing  114 - 2 . It will be appreciated, however, that the engine  100  could be implemented with more than this number of bearings  114 . The type of bearings  114  that are used may also vary, but in the depicted embodiment at least one of the bearings  114 , and specifically the aft bearing  114 - 2 , is a hydrodynamic gas film bearing. The hydrodynamic gas film bearing  114 - 2  may be implemented using any one of numerous types of self-actuating hydrodynamic gas film bearing. Moreover, although the depicted hydrodynamic gas film bearings  114  provide radial support, it will be appreciated that the bearing(s)  114  can also be configured to provide axial (thrust) support or both radial and axial support. The hydrodynamic gas film bearing  114  can be a compliant hydrodynamic gas film bearing, one example of which is a foil bearing. 
     As is generally known, a hydrodynamic gas film bearing runs on a film of gas, and during operation generates heat. To remove the heat that is generated, a flow of cooling gas is supplied to the hydrodynamic gas film bearing. Thus, the gas turbine engine  100  also preferably includes a hydrodynamic gas film bearing cooling gas control system  120  to regulate the supply the flow of cooling gas to the hydrodynamic gas film bearing  114 - 2 . The hydrodynamic gas film bearing cooling gas control system  120  is coupled to receive a flow of cooling gas from a pressurized source, and to controllably supply the cooling gas to the hydrodynamic gas film bearing  114 - 2 . In the depicted embodiment, the pressurized gas source is the compressor  102 , and hence the cooling gas is air. It will be appreciated, however, that the pressurized gas source may be any one of numerous other sources of pressurized cooling gas, either within or external to the gas turbine engine  100 , and that the cooling gas may be any one of numerous suitable gaseous fluid media including, for example, air, helium, zeon, and nitrogen, just to name a few. It will additionally be appreciated that the hydrodynamic gas film bearing cooling gas control system  120  may be variously configured to implement its functionality. One particular configuration is schematically depicted in  FIG. 2 , and will now be described. 
     In the configuration depicted in  FIG. 2 , the hydrodynamic gas film bearing cooling gas control system  120  includes a supply conduit  202  and a flow control device  204 . The supply conduit  202  is coupled to receive a flow of cooling gas from a cooling gas supply source  206 . The supply conduit  202  is additionally in fluid communication with the hydrodynamic gas film bearing  114 , and is thus configured to supply the flow of cooling gas to the hydrodynamic gas film bearing  114 . As noted above, in the context of a gas turbine engine, such as the gas turbine engine  100  depicted in  FIG. 1 , the cooling gas supply source  206  is preferably the compressor  102  (or the above described bleed air system that is supplied by the compressor  102 ), though it could be any one of numerous other sources. 
     The flow control device  204  is coupled to, or otherwise mounted on, the supply conduit  202 . The flow control device  204  is configured to be responsive to a physical characteristic of the cooling gas or the ambient environment (or both) to move between a plurality of positions, to thereby vary the flow of cooling gas, through the supply conduit  202 , to the hydrodynamic gas film bearing  114 . It will be appreciated that the physical characteristic(s) of the cooling gas or the ambient environment to which the flow control device  204  is responsive may vary, and may include one or more of cooling gas temperature, cooling gas pressure, ambient temperature, and ambient pressure, just to name a few. The flow control device  204  may additionally be configured to be responsive to one or more machine (e.g., gas turbine engine  100 ) conditions. Such machine conditions may also vary, and may include, for example, one or more of machine rotational speed, machine attitude, and machine component temperatures, just to name a few. 
     To carry out the above-described functionality, the flow control device  204  may be variously implemented and configured; however, in the embodiment depicted in  FIG. 2 , the flow control device  204  is implemented and configured as a multi-position valve. It will additionally be appreciated that the flow control device  204  may implemented using any one of numerous types of self-actuating flow control devices, or it may be controlled by a monitoring system. A self-actuating flow control device, as is generally known, includes a mechanical or other type of feature (e.g., a diaphragm, temperature responsive material, etc.) that automatically adjusts the position of the flow control device  204  in response to a change in a physical characteristic of the cooling gas, machine condition, and/or the ambient environment. If, however, the flow control device  204  is controlled by a monitoring system, the flow control device  204  will include a flow control device actuator  208 , and the hydrodynamic gas film bearing cooling gas control system  120  will additionally include one or more sensors  212  and a control  214 . The sensors  212  (e.g.,  212 - 1 ,  212 - 2 ,  212 - 3 , . . .  212 -N) are each configured to sense a physical characteristic of the cooling gas and/or ambient environment, and to supply a sensor signal representative thereof to the control  214 . The control  214  is in operable communication with the flow control device actuator  208  and the sensors  212 . The control  214  receives the sensor signals from the sensors  212  and is configured, in response to the sensor signals, to supply flow control device commands to the flow control device actuator  208 . The flow control device actuator  208 , in response to the flow control device commands, positions the flow control device  204  to the commanded position. It will be appreciated that the number of sensors  212 , and the physical phenomena that are sensed thereby, may vary. 
     In addition to variations in actuation configuration, the flow control device  204  may also be configured to implement various positional schemes. For example, when the flow control device  204  is implanted as a valve, it and various other components within the hydrodynamic gas film bearing cooling gas control system  120  (e.g., flow control device actuator  208  and control  214 ), if needed, may be configured and controlled to be positioned to a closed position, a full-open position, and any partial-open position between the closed and full-open position. With this type of configuration, the flow control device  204  may be used to continuously vary the flow of cooling to hydrodynamic gas film bearing  114 . Alternatively, the flow control device  204  may be configured and controlled to move between just two positions, which may also vary. For example, the two positions may be the closed and full-open positions, the closed and a partially-open position, a partially-open and the full-open positions, or two different partially-open positions. With this type of configuration, the flow control device  204  may be used to vary the flow of cooling gas to the hydrodynamic gas film bearing  114  between two flow conditions—a high flow condition and a low flow condition. 
     As  FIG. 2  additionally depicts, the hydrodynamic gas film bearing cooling gas control system  120  may also include a flow restriction  216 . The flow restriction  216 , if included, is configured to provide a step-down in cooling gas pressure, and may be positioned either downstream of the flow control device  204 , as depicted in  FIG. 2 , or upstream of the flow control device  204 . It will be appreciated that the flow restriction  216  may be variously implemented and configured, but in the depicted embodiment, the flow restriction is implemented and configured as an orifice having a cross sectional flow area that provides the step-down in cooling gas pressure. It will additionally be appreciated that if a step-down in pressure is not needed or if a suitable step down in pressure is provided by the flow control device  204  and/or the size and/or length of the supply conduit  202 , then the flow restriction  216  may not be included. As such, the flow restriction  216  is depicted in  FIG. 2  in phantom. 
     The hydrodynamic gas film bearing cooling gas control system  120  described above and depicted in  FIG. 2  includes a single path and an adjustable flow control device  204  to vary cooling gas flow to the hydrodynamic gas film bearing  114 . In alternative embodiments, the hydrodynamic gas film bearing cooling gas control system  120  is implemented using on/off flow control devices and multiple paths. Each of the alternative multi-path hydrodynamic gas film bearing cooling gas control systems  120 , which will be described momentarily, includes multiple cooling gas supply paths between the cooling gas supply source and the hydrodynamic gas film bearing  114 . One of the cooling gas supply paths is sufficient for the least limiting condition and does not include a flow control device. When the hydrodynamic gas film bearing  114  is operated under conditions that require more cooling gas flow than this one cooling gas path can provide, the flow control devices associated with the other cooling gas supply paths may be opened. Various embodiments of exemplary multi-path hydrodynamic gas film bearing cooling gas supply systems  120  are depicted in  FIGS. 3-5 , and will now be described. 
     Referring first to  FIG. 3 , the depicted multi-path hydrodynamic gas film bearing cooling gas control system  120 ′ includes a plurality of supply conduits  302  (e.g.,  302 - 1 ,  302 - 2 ,  302 - 3 ) and a plurality of flow control devices  304  (e.g.,  304 - 1 ,  304 - 2 ). The supply conduits  302 , which include a first supply conduit  302 - 1 , a second supply conduit  302 - 2 , and a third supply conduit  302 - 3 , are each coupled to receive a flow of cooling gas from a cooling gas supply source  306 . The supply conduits  302  are each additionally in fluid communication with the hydrodynamic gas film bearing  114 , and are thus configured to supply the flow of cooling gas to the hydrodynamic gas film bearing  114 . As with the previous embodiment, the cooling gas supply source  306 , in the context of a gas turbine engine, such as the gas turbine engine  100  depicted in  FIG. 1 , is preferably the compressor  102  (or the bleed air system that is supplied by the compressor  102 ), though it could be any one of numerous other sources. 
     The flow control devices  304 , which include a first flow control device  304 - 1  and a second flow control device  304 - 2 , are each coupled to, or otherwise mounted on, the first supply conduit  302 - 1  and the second supply conduit  302 - 2 , respectively. The flow control devices  304  are each configured to be responsive to a physical characteristic of the cooling gas or the ambient environment (or both) to move between a plurality of positions, to thereby vary the flow of cooling gas, through the supply conduit  202 , to the hydrodynamic gas film bearing  114 . As before, it will be appreciated that the physical characteristic(s) of the cooling gas or the ambient environment to which the flow control devices  304  are responsive may vary, and may include one or more of cooling gas temperature, cooling gas pressure, ambient temperature, and ambient pressure, just to name a few. The flow control devices  304  may additionally be configured to be responsive to one or more machine (e.g., gas turbine engine  100 ) conditions. Such machine conditions may also vary, and may include, for example, one or more of machine rotational speed, machine attitude, and machine component temperature, just to name a few. 
     The flow control devices  304  may be configured and controlled to continuously vary the flow of cooling to hydrodynamic gas film bearing  114 . Preferably, however, the flow control devices are configured and controlled to move between just two positions. The two positions may vary, and may include the closed and full-open positions, the closed and a partially-open position, a partially-open and the full-open positions, or two different partially-open positions. Preferably, however, the two positions are the closed and full-open positions. 
     As with the embodiment depicted in  FIG. 2 , the flow control devices  304  may be variously implemented and configured; however, in the embodiment depicted in  FIG. 3 , each flow control device  304  is implemented and configured as a multi-position valve. It will additionally be appreciated the flow control devices  304  may be implemented using any one of numerous types of self-actuating flow control devices, or the flow control devices  304  may be controlled by a monitoring system. If the flow control devices  304  are controlled by a monitoring system, each flow control device  304  will include a flow control device actuator (for clarity, not depicted in  FIG. 3 ), and the hydrodynamic gas film bearing cooling gas control system  120 ′ will include one or more sensors  312  and a control  314 . The one or more sensors  312  and control  314 , if included, are preferably configured to function at least substantially identical to the sensors  212  and control  214  depicted in  FIG. 2 . As such, the descriptions thereof will not be repeated. 
     The depicted hydrodynamic gas film bearing cooling gas control system  120 ′ may also include one or more flow restrictions  316  (e.g.,  316 - 1 ,  316 - 2 ,  316 - 3 ). The flow restrictions  316 , if included, are associated, one each, with each of the supply conduits  302 . It will be appreciated that the flow restrictions  316  may be variously implemented and configured, but in the depicted embodiment, each flow restriction  316  is implemented and configured as an orifice, each having a cross sectional flow area, which may or may not be equal, and that provides a step-down in cooling gas pressure. The flow restrictions  316  may additionally be variously positioned within the system  120 ′. It will be appreciated that if a step-down in pressure is not needed or if a suitable step down in pressure is provided by the flow control devices  304  and/or the size and/or length of the supply conduits  302 , then one or more of the flow restrictions  316  may not be included. As such, the flow restrictions  316  are depicted in  FIG. 3  in phantom. 
     The multi-path hydrodynamic gas film bearing cooling gas control system  120 ″ depicted in  FIG. 4  is substantially similar to the system  120 ′ depicted in  FIG. 3 . Thus, like reference numerals in  FIGS. 3 and 4  refer to like components, and detailed descriptions of each component need not, and will not, be provided. As may be readily apparent, the difference between the two systems  120 ′,  120 ″ is that in the system  120 ″ depicted in  FIG. 4 , the hydrodynamic gas film bearing  114  is supplied with a flow of cooling via only one supply conduit  302 , rather than via multiple independent supply conduits  302 - 1 ,  302 - 2 , and  302 - 3 . 
     The systems  120 ′,  120 ″ depicted in  FIGS. 3 and 4  are each implemented with three cooling flow paths. It will be appreciated, however, that this number of cooling flow paths is merely exemplary, and that the systems  120 ′,  120 ″ may be implemented with more or less than this number of cooling flow paths. It will additionally be appreciated that the locations of the supply conduits  302 , the flow control devices  304 , and the flow restrictions  316  (if included) are merely exemplary, and may vary. Moreover, the set points at which the flow control devices  304  change position may vary, and the sizes of the supply conduits  302  and flow restrictions  316 , both within and between systems, may also vary. 
     Turning now to  FIG. 5 , another multi-path hydrodynamic gas film bearing cooling gas control system  120 ′″ is depicted. This system  120 ′″ includes a supply conduit  502 , a plurality of flow restrictions  504  (e.g.,  504 - 1 ,  504 - 2 ), and a flow control device  506 . The supply conduit  502  is coupled to receive a flow of cooling gas from a cooling gas supply source  508 . The supply conduit  502  is additionally in fluid communication with the hydrodynamic gas film bearing  114 , and is thus configured to supply the flow of cooling gas to the hydrodynamic gas film bearing  114 . As with all of the previously-described embodiments, the cooling gas supply source  508 , in the context of a gas turbine engine, such as the gas turbine engine  100  depicted in  FIG. 1 , is preferably the compressor  102  (or the bleed air system that is supplied by the compressor  102 ), though it could be any one of numerous other sources. 
     The flow restrictions  504 , which include a first flow restriction  504 - 1  and a second flow restriction  504 - 2 , are each disposed between the supply conduit  502  and the flow control device  506 . The first flow restriction  504 - 1  has a first cross sectional flow area and the second flow restriction  504 - 2  has a second cross sectional flow area that is greater than the first cross sectional flow area. Hence, for the same set of conditions, cooling gas flow through the second flow restriction  504 - 2  will be greater than it would be through the first flow restriction  504 - 1 . As with each of the previously described embodiments, tt will be appreciated that the flow restrictions  504  may be variously implemented and configured. In the depicted embodiment, however, each flow restriction  504  is implemented and configured as an orifice. 
     The flow control device  506  is disposed upstream of each of the flow restrictions  504 , and is preferably implemented using a multi-position flow control device. The flow control device  506  is preferably configured to be responsive to a physical characteristic of the cooling gas or the ambient environment (or both) to move between a plurality of positions. In the depicted embodiment, the plurality of positions is two—a first position and a second position. When the flow control device  506  is in the first position, cooling gas from the cooling gas supply source  508  is directed through the flow control device  506  and into and through the first flow restriction  504 - 1 . Conversely, when the flow control device  506  is in the second position, cooling gas from the cooling gas supply source  508  is directed through the flow control device  506  and into and through the second flow restriction  504 - 2 . Thus, the flow of cooling gas, through the supply conduit  502 , to the hydrodynamic gas film bearing  114  is varied by varying the position of the flow control device  506 . In other embodiments, the flow control device  506  may be movable to more than two positions, and may include more than two flow restrictions, if needed or desired. With these other embodiments, the flow control device  506  may be positioned to simultaneously allow cooling gas flow through two or more flow restrictions  504 . 
     As with all of the previously described embodiments, it will be appreciated that the physical characteristic(s) of the cooling gas or the ambient environment to which the flow control device  506  is responsive may vary, and may include one or more of cooling gas temperature, cooling gas pressure, ambient temperature, and ambient pressure, just to name a few. The flow control device  506  may additionally be configured to be responsive to one or more machine (e.g., gas turbine engine  100 ) conditions. Such machine conditions may also vary, and may include, for example, one or more of machine rotational speed, machine attitude, and machine component temperature, just to name a few. Moreover, the flow control device  506  may be variously implemented and configured. For example, the flow control device  506  may be implemented as a mechanical means, such as a sliding plate or similar device, that is configured to selectively cover and uncover (either partially or fully) the flow restriction(s)  504 . In the embodiment depicted in  FIG. 5 , however, the flow control device  506  is implemented and configured as a multi-position switch valve. 
     The flow control device  506  may also be implemented using any one of numerous types of self-actuating flow control devices, or the flow control device  506  may be controlled by a monitoring system. If the flow control device  506  is controlled by a monitoring system, it will include a flow control device actuator (for clarity, not depicted in  FIG. 5 ), and the hydrodynamic gas film bearing cooling gas control system  120 ′″ will include one or more sensors  512  and a control  514 . The one or more sensors  512  and control  514 , if included, are preferably configured to function at least substantially identical to the sensors  212  and control  214  depicted in  FIG. 2 . As such, the descriptions thereof will not be repeated. 
     Although the hydrodynamic gas film bearing cooling gas control systems  120  described above are configured to adaptively control the supply of cooling gas to a single hydrodynamic gas film bearing  114 , it will be appreciated that these are merely exemplary and that the hydrodynamic gas film bearing cooling gas control systems  120  may be configured to supply two or more hydrodynamic gas film bearings, if need or desired. Moreover, if a machine, such as the above-described gas turbine generator  100 , includes two or more hydrodynamic gas film bearings  114 , then two or more hydrodynamic gas film bearing cooling gas control systems  120 , one associated with each of the bearings  114 , could also be used. Further, some machines, such as multi-spool gas turbine engines, may include two or more shafts, each of which may be rotationally mounted using one or more hydrodynamic gas film bearings. In this latter case, the hydrodynamic gas film bearing cooling gas control systems  120  could be configured to measure conditions associated with one shaft, but control cooling gas flow to the hydrodynamic gas film bearing(s) on another shaft. An exemplary embodiment in which the hydrodynamic gas film bearing cooling gas control system  120  is configured to supply two hydrodynamic gas film bearings  114 - 1 ,  114 - 2  is depicted in  FIG. 6 . An exemplary embodiment in which two hydrodynamic gas film bearing cooling gas control systems  120  separately control cooling gas flow to two different hydrodynamic gas film bearings  114 - 1 ,  114 - 2  is depicted. An exemplary embodiment in which a hydrodynamic gas film bearing cooling gas control system  120  is configured to measure conditions associated with one shaft  112 - 1 , and control cooling gas flow to the hydrodynamic gas film bearing(s)  114  on another shaft  112 - 2 . 
     The various embodiments described herein are not limited to those explicitly depicted. Rather, some or all of the features associated with each of the depicted embodiments may be implemented with one or more of the other embodiments. For example, the embodiment depicted in  FIG. 2  may be implemented to include one of more of the features of the embodiments depicted in  FIGS. 3-5 , and so on. Moreover, the embodiments depicted in  FIGS. 2-4  may include any combination of additional controlled and uncontrolled paths, some, all, or none of which may include a flow restriction. The embodiment depicted in  FIG. 5  may include more than two flow paths, each with variously sized flow restrictions. And, as was alluded to when describing the embodiment of  FIG. 5 , the flow control device of that embodiment may be configured to allow cooling gas flow through more than one flow restriction at a time, to thereby vary overall flow resistance. The embodiment depicted in  FIG. 5  may also be implemented to include one or more of the features of the embodiments depicted in  FIGS. 2-4  (e.g., one or more controlled and/or uncontrolled flow paths). Additionally, in each of the various embodiments the configuration of the supply conduit(s) may vary. For example, embodiments may be implemented with multiple supply conduits, a single supply conduit, multiple supply conduits in which one or more supply conduit has multiple cooling gas inputs. 
     The hydrodynamic gas film bearing cooling gas control systems described herein allows for optimized cooling gas flow to one or more hydrodynamic gas film bearings across a variety of operating conditions. 
     While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims.