Abstract:
A method for operating a gas turbine engine including a compressor is provided. The method includes defining a predetermined concentration, placing at least one sensor in an inlet of the gas turbine engine, detecting a sand and dust concentration value using the at least one sensor; and deploying a boot to facilitate preventing particles from entering the compressor when the sand and dust concentration value equals or exceeds the predetermined concentration. The boot includes a plurality of fluid exit slots such that clean air is facilitated to be adhered to a flow path surface downstream from the boot.

Description:
BACKGROUND OF THE INVENTION 
   This invention relates generally to gas turbine engines, and more particularly, to adaptive inertial particle separators and methods of use. 
   Sand and dust ingestion in gas turbine engines may adversely affect engine performance and reliability, and may also increase the frequency of repair and maintenance required for the engines. Because flight readiness depends at least partially on reliably and properly functioning engines, reducing the occurrence of, and/or the effects of, sand and dust ingestion should facilitate enhancing the reliability of the engines. 
   Various methods are employed to facilitate reducing sand and dust concentrations channeled via the inlet airflow to the engine compressor. For example, known inertial particle separator (IPS) systems perform well in any weather conditions, are highly reliable, are integrated into the engine, but may not provide adequate separation efficiency during severe sand and dust conditions. Inertial inlet particle separators work by imparting momentum and trajectory on sand and dust particles to channel such particles away from the fluid stream entering the gas turbine engine. The particles removed are then collected or scavenged into an overboard dump. However, the same features that facilitate the separation of sand and dust particles from the inlet air, also cause inlet pressure losses that may detrimentally effect gas turbine engine performance. Because of the permanent nature of known IPS systems, engine performance loss is incurred in clean air and sandy air conditions. 
   During operation, fluid flow into a gas turbine engine inlet is channeled downstream towards an entry channel. Downstream from a convex section, fluid flow is divided into two fluid streams. One of the streams, known as a dirty fluid flow, is channeled towards a dirty fluid channel. Debris, such as birds, and particles of debris, such as snow and/or ice particles, flow through the dirty fluid channel and into the IPS scavenge system wherein the debris is ejected from gas turbine engine. The other fluid stream, known as a clean fluid flow, is channeled into a clean fluid channel. To facilitate “clean” flow into the clean fluid channel, the clean fluid flow is forced to make a sharp turn around a convex section. Most debris will not be capable of changing direction at the turn, due to the greater inertia and momentum of the debris particles. Consequently, most debris will be channeled into the dirty fluid channel, thus facilitating a flow of clean fluid into the gas turbine engine. IPS systems of this type facilitate removal of large sand particles and debris, but generally such IPS systems are not as effective in removing smaller particles or debris. 
   Some known helicopters are fitted with bulky barrier filters to address severe sand conditions. Although such filters satisfactorily remove sand and dust from the air, known filters are heavy, detrimentally effect engine performance, require increased maintenance, and are unable to operate in icing conditions. Moreover, known filters also cause a pressure drop at the inlet of the gas turbine engine that also adversely affects engine performance. Furthermore, known filters may also be susceptible to plugging with sand and dust. 
   BRIEF DESCRIPTION OF THE INVENTION 
   In one aspect, a method for operating a gas turbine engine including a compressor is provided. The method includes defining a predetermined concentration, placing at least one sensor in an inlet of the gas turbine engine, detecting a sand and dust concentration value using the at least one sensor and deploying a boot to facilitate preventing particles from entering the compressor when the sand and dust concentration value equals or exceeds the predetermined concentration. The boot includes a plurality of fluid exit slots such that clean air is facilitated to be adhered to a flow path surface downstream from the boot. 
   In another aspect, an inertial particle separation system for a gas turbine engine is disclosed. The system includes an inlet of the gas turbine engine and an inflatable boot coupled to a surface defining a flow path through the inlet. The boot includes a plurality of fluid exit slots configured to facilitate clean air to adhere to a flow path surface downstream from the boot. The system also includes means for causing the boot to be deployed. 
   In yet another aspect, a dual mode inertial particle separation apparatus for a gas turbine engine is provided. The apparatus includes an inertial particle separator including an entry channel and a flow path, the inertial particle separator facilitates effective removal of sand particles and debris from fluid in the entry channel during a first mode of operation of the inertial particle separator. The apparatus also includes an inflatable boot coupled to a surface of the inertial particle separator and defining the flow path. The boot is inflated during a second mode of operation of the inertial particle separator to facilitate increasing removal efficiency of sand particles and debris from fluid in the entry channel. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a plan view of a portion of an exemplary helicopter including two gas turbine engine assemblies; 
       FIG. 2  is an enlarged cross-sectional view of a portion of a known gas turbine engine inlet that may be used with the engine assemblies shown in  FIG. 1 ; 
       FIG. 3  is an enlarged cross-sectional view of a portion of a gas turbine engine inlet that may be used with the engine assembly shown in  FIG. 2 , and includes an inflatable flow path boot; 
       FIG. 4  is an enlarged view of a portion of the inlet shown in  FIG. 2  and includes a deployed inflatable flow path boot; 
       FIG. 5  is a block diagram illustrating exemplary control logic for use with the inlet shown in  FIGS. 2 and 3 ; and 
       FIG. 6  is a flowchart illustrating an exemplary method for determining when to deploy the inflatable flow path boot shown in  FIGS. 3 and 4 . 
       FIG. 7  is a flowchart illustrating another exemplary method for determining when to deploy the inflatable flow path boot shown in  FIGS. 3 and 4 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  is a plan view of a portion of an exemplary helicopter  10  that includes two gas turbine engine assemblies  12 . Each gas turbine engine assembly  12  includes a pair of gas turbine engines  14 , each of which includes an inlet  16  and an exhaust  18 . The gas turbine engines  14  are oriented symmetrically with respect to an axis of symmetry  20  extending axially between the gas turbine engines  14 . Moreover, gas turbine engines  14  are mounted within an engine compartment  22  defined by a helicopter fuselage  24 . A rear drive shaft  26  extends from each gas turbine engine  14  to a main transmission  28 . In other designs, drive shaft  26  may extend out of the front of each engine  14 . 
     FIG. 2  is an enlarged cross-sectional view of a portion of gas turbine engine inlet  16 . Inlet  16  may be integral with engine  14  or may be separate from engine  14 . In the exemplary embodiment, inlet  16  functions as an inertial particle separator (IPS) and includes an entry channel  30  defined by an outer surface  32  and an inner surface  34 . Inner surface  34  includes a convex section  36 . A splitter  38  bifurcates entry channel  30  into a clean-fluid channel  40  and a dirty-fluid channel  42 . Clean fluid channel  40  is defined by a lower surface  39  of splitter  38  and inner surface  34 . Clean fluid channel  40  extends from inner surface convex section  36  to a compressor  44  included within the gas turbine engine  14 . Dirty fluid channel  42  is defined by an upper surface  37  of splitter  38  and outer surface  32  and extends from convex section  36  to an IPS scavenge system (not shown). The IPS scavenge system is powered by a blower or an exhaust ejector. It should be appreciated that the term “fluid” as used herein includes any material or medium that flows, including but not limited to, gas, air and liquids. 
     FIG. 3  is an enlarged cross-sectional view of a portion of an exemplary gas turbine engine inlet  16 . In the exemplary embodiment, an inflatable flow path boot  50  that may be used with gas turbine engine  14  is coupled to the convex section  36  of inner surface  34  and a sensor  48  is coupled to outer surface  32 . The inflatable flow path boot  50  may have any geometric configuration that enables inlet  16  to function as described herein. Furthermore, flow path boot  50  may be made from any material capable of withstanding the harsh operating environment of gas turbine engine inlet  16 . 
   In the exemplary embodiment, inflatable flow path boot  50  is deployed using bleed air channeled from gas turbine engine  14 . Specifically, a duct  52  extends between boot  50  and a low pressure fluid source, such as but not limited to, the low pressure compressor  44 . A control valve  54  facilitates controlling fluid flow from the low pressure source to flow path boot  50 . 
   In the exemplary embodiment, inflatable flow path boot  50  is secured to inner surface  34  and is deployable from a non-inflated operating state to an inflated operating state. During operation of gas turbine engine  14 , when sand and dust, for example, are not being drawn into inlet  16 , flow path boot  50  remains deflated and in its non-inflated state. In the non-inflated state, flow path boot  50  is substantially flush against inner surface  34  within convex section  36 . However, when an unacceptable concentration of sand and dust is encountered or sensed entering inlet  16 , flow path boot  50  is inflated such that the geometry of entry flow channel  30  and clean fluid channel  40  are changed. Specifically, the inflated flow path boot  50  effectively reshapes the convex section  36  of the inner surface  34  and narrows the throat area by forcing the top surface  51  of boot  50  towards inlet outer surface  32 . In doing so, top surface  51  of boot  50  reduces the width of the entry channel  30  and causes a sharper flow path turn to be defined at a trailing edge  35  of convex section  36 . Moreover, inflated boot  50  creates a sharper turn for the fluid side that most of the sand and dust particles will not be capable of undergoing due to the inertia of such particles. Consequently, a higher percentage of sand and dust particles will be channeled into the dirty fluid channel  42 , such that sand and dust separation efficiency is facilitated to be enhanced. 
     FIG. 4  is an enlarged view of convex section  36  and includes an inflated flow path boot  50  extending therefrom. Flow path boot  50  includes a plurality of fluid exit slots  56 . The fluid exit slots  56  facilitate returning energy into a fluid boundary layer flowing past boot  50 . As such, clean fluid flow adheres more closely to a top surface  51  of flow path boot  50  and is more able to make the sharp turn at the trailing edge  53  of the convex section defined by the top surface  51  and into clean fluid channel  40 . This feature allows the clean fluid flow to go around the sharper turn without separating from the top surface  51  and inner surface  34 , without causing high pressure drop and flow distortion to compressor  44 . It should be appreciated that fluid exit slots  56  may have any geometric shape that enables boot  50  to function as described herein, such as, but not limited to a cut in the boot  50 , a rectangular opening, and/or a series of circular openings. Moreover, any number of slots  56  may be provided that enables boot  50  to function as described herein. 
   Sensor  48  senses the concentration of sand and dust in entry channel  30 . Sensor  48  may be, but is not limited to being, a side optical device and/or a “sand sniffer” in combination with a particle analyzer. It should be appreciated that sensor  48  may be any device that facilitates determining concentrations of sand and dust in gas turbine engine inlet  16 . It should also be appreciated that although this exemplary embodiment is described using a single sensor  48  disposed in the front area of inlet  16  on outer surface  32 , in various other exemplary embodiments sensor  48  may be installed on any surface or any other location that enables the fluid flow within inlet  16  to be analyzed as described herein. Moreover, it should be appreciated that although this exemplary embodiment is described as including only a single sensor  48 , a plurality of sensors  48  may be used to determine the concentration of sand and dust in entry channel  30 . Sensor  48  communicates with a controller  100  by sending electrical signals representative of sand and dust concentrations to an input/output circuit  110 . 
     FIG. 5  is a block diagram illustrating an exemplary control logic and system controller  100  for use in determining when boot  50  should be deployed. In the exemplary embodiment, the controller  100  includes an input/output circuit  110 , a memory  120  and a processing circuit  130 . The controller  100  communicates with sensor  48  and with control valve  54 . 
   It should be understood that each of the circuits shown in  FIG. 5  can be implemented as portions of a suitably programmed general purpose processor. As used herein, the term “processor” may include any programmable system including systems using microcontrollers, reduced instruction set circuits (RISC), application specific integrated circuits (ASICs), logic circuits, and any other circuit or processor capable of executing the functions described herein. The above examples are exemplary only, and are thus not intended to limit in any way the definition and/or meaning of the term “processor”. 
   The input/output interface circuit  110  receives signals transmitted to controller  100  from sand monitoring sources, such as sensor  48 . In this exemplary embodiment, controller  100  receives electrical signals from the sensor  48  that represent the concentration of sand and dust in the fluid. Additionally, input/output interface circuit  110  outputs signals produced by controller  100 . 
   The memory  120  can include one or more of a predetermined concentration portion  122 , a sand and dust concentration readings portion  124 , and/or a control valve adjustment instructions portion  126 . The predetermined concentration portion  122  stores a predetermined value for the concentration of sand and dust in the fluid. Portion  124  stores sensor  48  readings taken during operation of gas turbine engine  14 , and portion  126  stores instructions for opening and closing control valve  54 . 
   Memory  120  can be implemented using any appropriate combination of alterable, volatile or non-volatile memory or non-alterable, or fixed, memory. The alterable memory, whether volatile or non-volatile, can be implemented using any one or more of static or dynamic RAM (Random Access Memory), a floppy disk and disk drive, a writeable or re-writeable optical disk and disk drive, a hard drive, flash memory or the like. Similarly, the non-alterable or fixed memory can be implemented using any one or more of ROM (Read-Only Memory), PROM (Programmable Read-Only Memory), EPROM (Erasable Programmable Read-Only Memory), EEPROM (Electrically Erasable Programmable Read-Only Memory), an optical ROM disk, such as a CD-ROM or DVD-ROM disk, and disk drive or the like. 
   In this exemplary embodiment, processing circuit  130  compares each sand and dust concentration reading  124  with the predetermined concentration of sand and dust stored in the predetermined concentration portion  122 . The predetermined concentration represents a threshold value that the sand and dust concentration should not equal or exceed. 
     FIG. 6  is a flowchart illustrating an exemplary method for determining when inflatable flow path boot  50  (shown in  FIGS. 3 and 4 ) should be deployed. Initially, a set of predetermined concentrations is defined at  72 . Then in step  74 , sensor  48  generates a concentration reading corresponding to the amount of sand and dust in the fluid flowing in entry channel  30  (shown in  FIG. 3 ). The concentration reading from step  74  is compared at  76  against the predetermined concentration to determine whether the concentration reading is less than the predetermined concentration. When the concentration reading is less than the predetermined concentration, operation proceeds to step  78 . Otherwise, operation proceeds to step  86 . The following discussion describes operation proceeding to step  78 , then describes operation proceeding to step  86 . 
   At step  78 , a decision is made regarding whether the flow path boot  50  is inflated. If boot  50  is not inflated, operation proceeds to step  80  where a decision is made regarding whether additional sand and dust concentration readings are warranted. If additional readings are warranted, operation continues to step  74 . If no additional readings are warranted, operation continues to step  88  wherein operation ends. At step  78 , if boot  50  is inflated, operation proceeds to step  82 . 
   At step  82 , a signal is sent from the input/output circuit  110  to control valve  54 . The signal instructs control valve  54  to close. Accordingly, fluid stops flowing to flow path boot  50  causing boot  50  to deflate. Operation then proceeds to step  84 . At step  84 , a decision is made regarding whether additional sand and dust concentration readings are warranted. If additional readings are warranted, operation continues to step  74 . If no additional readings are warranted, operation continues to step  88  wherein operation ends. 
   At step  76 , when the concentration reading is not less than the predetermined concentration, operation proceeds to step  86 . At step  86 , a signal is sent from the input/output circuit  110  to control valve  54 . The signal instructs control valve  54  to open. Accordingly, fluid flows to flow path boot  50  causing boot  50  to inflate. Operation then proceeds to step  84 . At step  84 , a decision is made regarding whether additional sand and dust concentration readings are warranted. If additional readings are warranted, operation continues to step  74 . If no additional readings are warranted, operation continues to step  88  wherein operation ends. Thus, this exemplary embodiment enables craft to operate more efficiently when free of sand and dust conditions, versus operating with boot  50  constantly deployed. 
     FIG. 7  is a flowchart illustrating another exemplary method for determining when inflatable flow path boot  50  (shown in  FIGS. 3 and 4 ) should be deployed. Initially, an aircraft operator, or pilot, detects sand and dust conditions at  90 . Then in step  92 , the operator uses an activator (not shown) to open control valve  54 , such that fluid flows to flow path boot  50  causing boot  50  to inflate. It should be appreciated that the activator may be any kind of activator that enables control valve  54  to function as described herein. When the aircraft operator does not detect a sand and dust condition at  93 , operation proceeds to step  94 . At step  94 , the aircraft operator uses the activator (not shown) to close control valve  54 , such that fluid ceases to flow to control path boot  50  causing boot  50  to deflate. Thus, this exemplary embodiment also enables craft to operate more efficiently when free of sand and dust conditions, versus operating with boot  50  constantly deployed. 
   The exemplary embodiments described herein use the available space around the nose gearbox of a gas turbine engine  14  to cause fluid entering the inlet to turn abruptly through a two dimensional inertial particle separator before transitioning into the gas turbine engine  14  itself. For example, if applied to a CH53 aircraft, the system could replace the aircraft inlet duct and EAPs system and is substantially more compact and lighter. Also disclosed herein, as part of the system, is an inflatable flow path boot  50  powered by low pressure engine bleed fluid. The bleed fluid may be controlled automatically using the controller  100  or, alternatively, may be controlled by aircraft operator action. Using the bleed fluid, the flow path boot  50  creates a sharper turn for the fluid, which facilitates enhancing higher sand separation efficiency. Aerodynamically designed fluid exit slots  56  are provided in boot  50  to facilitate delaying or preventing flow separation of the fluid in the flow path from inner surface  34 , despite the sharp turning angle of the fluid at the trailing edge  53  of the convex section defined by the top surface  51 . 
   The combination of the flow path boot  50  and the fluid exit slots  56  offers a significant reliability advantage over conventional inertial particle separators. The fluid flow path only follows the aggressive turning configuration at the trailing edge  53  of the convex portion defined by the top surface  51  if there is fluid available to inflate boot  50  and to blow the boundary layer control fluid. Additionally, should the control valve  54  supplying fluid to the boot  50  malfunction, there is no risk of the inlet separating and causing an engine operability issue. 
   In each embodiment, the above-described inflatable boot with blowing slots facilitates sand and dust removal from the clean fluid entering the engine. More specifically, in each embodiment, the inflated boot creates a sharper turn that most sand and dust particles will not be capable of undergoing due to the inertia of such particles. As a result, during engine operation fewer sand and dust particles enter the engine. Accordingly, engine performance and component useful life are each facilitated to be enhanced in a cost effective and reliable manner. Moreover, the invention provides a means wherein existing inertial particle separators can be modified to facilitate enhancing turbine engine performance. 
   Exemplary embodiments of inertial particle separators are described above in detail. The inflatable boots are not limited to use with the specific inertial particles separator embodiments described herein, but rather, the inflatable boots can be utilized independently and separately from other inertial particle separator components described herein. For example, the inflatable boots described herein may be retrofitted in most helicopter engines and may be used for a wide range of flow control scenarios, including aircraft control surfaces. Moreover, the invention is not limited to the embodiments of the inflatable boots described above in detail. Rather, other variations of inflatable boot embodiments may be utilized within the spirit and scope of the claims. 
   While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.