Patent Publication Number: US-11391288-B2

Title: System and method for operating a compressor assembly

Description:
FEDERALLY SPONSORED RESEARCH 
     This invention was made with government support under contract number DTFAWA-10-C-00046 under the Federal Aviation Administration of the U.S. Government. The government may have certain rights in the invention. 
    
    
     FIELD 
     The present subject matter relates generally to methods and systems for operating a compressor assembly to avoid surge or stall at a turbo machine. 
     BACKGROUND 
     Compressor assemblies included in turbo machines may undergo surge or stall based on a plurality of factors. Compressor stall includes a local disruption in airflow through the compressor assembly. Compressor stall may include rotating stall, in which a portion of airfoils of a compressor assembly experience flow destabilization or stagnation (e.g., stall cells). For instance, compressor stall may include rotating stall cells in which relatively stagnant air rotates from airfoil to airfoil within a compressor stage rather than along the desired flow direction (e.g., along the axial direction of an axial compressor). 
     Axisymmetric stall or compressor surge includes flow oscillations or reverse airflows (i.e., flows opposite of the desired flow direction). Compressor surge may include an undesired expulsion of compressed air through a compressor inlet rather than a compressor outlet. Compressor surge may result from an inability of the compressor assembly to continue to pressurize or add work to compressed air. The limits of operation of a compressor assembly may be defined by a surge line (e.g., pressure ratio versus flow rate). During operation, as compressor assemblies become more highly loaded, disturbances in flow that may initialize as rotating stall may develop into compressor surge in less than one second. Furthermore, as a turbo machine operates over time and various conditions, wear and deterioration may reduce operability or performance of a compressor assembly, such as to make the compressor assembly more susceptible to compressor stall or surge. 
     Compressor stall or surge may result in damage of the compressor assembly and the turbo machine. Although various mechanisms are known for avoiding compressor stall or surge conditions, a known problem is detecting an upcoming surge or stall condition before the turbo machine surges or stalls, such as to perform maneuvers to avoid the condition. Additionally, a known problem is detecting the type of stall or surge condition to which the compressor assembly is approaching, as the type of surge or stall condition will at least in part be determinative of what changes in engine maneuvers are necessitated based on the specific type of surge or stall different from one another. Without detecting an upcoming stall or surge, or without detecting the type of upcoming stall or surge, turbo machine operators may be unable to avoid encountering compressor stalls or surges that may deteriorate the life of the turbo machine or result in uncommanded engine shutdowns, sudden losses in thrust, or overall damage to the turbo machine. Furthermore, without detecting the type of upcoming stall or surge, turbo machine operators may apply surge or stall mitigation maneuvers to little or no effect to avoid the specific type of surge or stall encountered. 
     BRIEF DESCRIPTION 
     Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention. 
     An aspect of the present disclosure is directed to a computer-implemented method for operating a compressor assembly. The method includes obtaining a first data set over a first period of time; obtaining a second data set over a second period of time after the first period of time; comparing the first data set and the second data set to determine a first correlation factor; comparing the first correlation factor to a first threshold, wherein the first threshold at least partially determines whether a stall precursor exists; removing mean values from the first data set and the second data set; comparing the first data set and the second data set each removed of mean values to determine a second correlation factor; comparing the second correlation factor to the first threshold, wherein comparing the second correlation factor to the first threshold at least partially determines whether the stall precursor comprises one of a spike stall precursor, a modal stall precursor, or a combination stall precursor; and classifying the stall precursor as either the spike stall precursor, the modal stall precursor, or the combination stall precursor. 
     Another aspect of the present disclosure is directed to a computing system for operating a turbo machine. The computing system is configured to perform operations, such as via a controller including a processor and memory configured to store instructions that, when executed by the processor, causes the processor to perform operations. The operations include obtaining a first data set over a first period of time; obtaining a second data set over a second period of time after the first period of time, wherein the second period of time is during a revolution of the turbo machine after obtaining the first data set over the first period of time; identifying whether a stall precursor exists at the turbo machine; and identifying a type of stall precursor, wherein the type of stall precursor comprises one of a spike stall precursor, a modal stall precursor, or a combination stall precursor. Identifying the type of stall precursor includes comparing the first data set and the second data set to provide a first correlation factor; removing mean values from the first data set and the second data set; determining a second correlation factor by comparing the first data set and the second data set each removed of mean values; and comparing the second correlation factor to a first threshold; and generating a control signal based at least on the identified type of stall precursor. 
     Yet another aspect of the present disclosure is directed to a turbo machine including a compressor assembly. The compressor assembly includes a sensor positioned at adjacent stages of compressor blade rows. The sensor is configured to obtain a performance parameter of a fluid through the compressor assembly. The turbo machine further includes a controller including a processor and memory configured to store instructions that, when executed by the processor, causes the processor to perform operations. The operations include obtaining, via the sensor, a first data set over a first period of time during rotation of the compressor assembly; obtaining, via the sensor, a second data set over a second period of time following the first period of time, wherein the second period of time corresponds to one or more revolutions of the compressor assembly after the first period of time; comparing the first data set and the second data set to determine a first correlation factor; removing mean values of the first data set and the second data set; determining a second correlation factor by comparing the first data set and the second data set each removed of mean values; determining a type of stall precursor at the compressor assembly, wherein determining the type of stall precursor is based at least on comparing the first correlation factor to a first threshold and comparing the second correlation factor to a magnitude threshold, and wherein the type of stall precursor is one of a spike stall precursor, a modal stall precursor, or a combination stall precursor; and operating the compressor assembly based at least on the determined type of stall precursor. 
     These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which: 
         FIG. 1  is an exemplary turbo machine including a controller configured to perform operations shown and described according to aspects of the present disclosure; 
         FIGS. 2-4  are flow charts outlining exemplary steps of methods for operating a compressor assembly; 
         FIG. 5  is a schematic of an exemplary system for operating a compressor assembly; 
         FIG. 6  is an exemplary graph of a performance parameter over time according to an aspect of the present disclosure; 
         FIG. 7  is an exemplary graph of a performance parameter over time according to an aspect of the present disclosure; 
         FIG. 8  includes exemplary graphs depicting comparisons of correlation factors to thresholds according to an aspect of the present disclosure; 
         FIG. 9  includes exemplary graphs depicting comparisons of correlation factors to thresholds according to an aspect of the present disclosure; 
         FIG. 10  includes exemplary graphs depicting comparisons of correlation factors to thresholds according to an aspect of the present disclosure; and 
         FIG. 11  includes an exemplary graph depicting comparison of correlation factors to thresholds according to an aspect of the present disclosure; and 
     
    
    
     Repeat use of reference characters in the present specification and drawings is intended to represent the same or analogous features or elements of the present invention. 
     DETAILED DESCRIPTION 
     Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. 
     As used herein, the terms “first”, “second”, and “third” may be used interchangeably to distinguish one component from another and are not intended to signify location or importance of the individual components. 
     The terms “upstream” and “downstream” refer to the relative direction with respect to fluid flow in a fluid pathway during normal or desired turbo machine or compressor assembly operation (e.g., without aerodynamic stall or surge). For example, “upstream” refers to the direction from which the fluid flows (e.g., from a forward end), and “downstream” refers to the direction to which the fluid flows (e.g., toward an aft end). It should be appreciated that although embodiments of the apparatus and methods shown and described herein may depict an axial flow compressor, embodiments of the turbo machine, compressor assembly, and/or methods provided herein may be applied to centrifugal compressors, reverse-flow turbo machines, or other applicable compressor or turbo machine configurations. 
     Approximations recited herein may include margins based on one more measurement devices as used in the art, such as, but not limited to, a percentage of a full scale measurement range of a measurement device or sensor. Alternatively, approximations recited herein may include margins of 10% of an upper limit value greater than the upper limit value or 10% of a lower limit value less than the lower limit value. 
     Embodiments of a method and system for operating a compressor assembly and turbo machine are generally provided. The methods and systems provided herein determine whether the compressor assembly and turbo machine is operating with a stall precursor. The methods and systems further identify or classify whether the stall precursor is a spike stall precursor, a modal stall precursor, or a combination stall precursor that includes spike stall and modal stall precursors. The spike stall precursor is indicative of the compressor assembly operating at or toward, but prior to, a spike stall condition. The modal stall precursor is indicative of the compressor assembly operating at or toward, but prior to, a modal stall condition. The combination stall precursor is indicative of the compressor assembly operating at or toward, a stall condition including both spike stall and modal stall. Various embodiments of the methods and systems provided herein further generating one or more control signals, control responses, or operations at the compressor assembly or turbo machine based at least on the determined stall precursor. 
     It should be appreciated that spike stalls, modal stalls, or combination stalls generally form differently at the compressor assembly. Modal stalls generally arise from relatively small amplitude airflow or pressure disturbances (e.g., relative to mean velocity of airflow), such as around a circumferential distance of a compressor at one or more rotating stages. Spike stalls generally arise from relatively large amplitude airflow or pressure disturbances, such as along relatively shorter circumferential distances of the compressor (e.g., along a portion of compressor blades). Spike stalls may generally define sharp pressure or velocity waveforms or spikes over time or rotor revolution in contrast to modal stalls. 
     Furthermore, spike stalls may generally form at, from, or proximate to a blade tip of a rotor assembly. Modal stalls may generally form at, from, or proximate to a blade root or hub of the rotor assembly (e.g., depicted at arrow  29  in  FIG. 1 ). Differences in formation of the stall may at least in part determine what operations or manoeuvres are performed to remove the stall condition or mitigate exasperation of the stall condition (e.g., mitigate development of compressor surge). The methods and systems provided herein may further include adjusting compressor loading or a rate of acceleration based at least on whether the compressor assembly and turbo machine include a spike stall precursor, a modal stall precursor, or a combination stall precursor. 
     It should be appreciated that, in various embodiments, operating the turbo machine is based specifically on the determined stall precursor such as to avoid formation of compressor stall or surge. Whether the turbo machine is approaching stall or surge based on the spike stall condition may necessitate adjustment in the operating mode of the turbo machine different from adjustment in operating mode when the turbo machine is approaching stall or surge based on conditions not including the spike stall condition. It should further be appreciated that, without determining specifically the spike stall condition or the modal oscillation condition, adjustments in operation of the turbo machine may fail to prevent stall or surge, as adjustments based on the spike stall precursor may be separate or different from adjustments based on the modal stall precursor. Additionally, or alternatively, adjustments based on the spike stall condition do not necessarily prevent stall or surge in contrast to adjustments based on the modal oscillation condition. Still further, methods or operations that may adjust for both modal and spike stall generally (i.e., not specific to one or the other of modal stall or spike stall) may undesirably reduce compressor or turbo machine operability or performance. Such reductions may lead to undesired additions or complications to the compressor assembly or turbo machine, thereby reducing performance, operability, or efficiency of the overall system. 
     As such, embodiments of the method and system provided herein beneficially determine whether the compressor assembly and turbo machine is operating toward a spike stall, a modal stall, or a combination stall condition. Operation of the compressor assembly and turbo machine, or adjustments thereto, may be performed to avoid stall or surge based on the determined stall precursor. Such determination may improve turbo machine operability, performance, efficiency, and durability. Furthermore, embodiments of the method and system provided herein may be implemented with existing turbo machines, such as via upgrades in software, computing device, controllers, etc., such as to improve compressor assembly performance or operability in existing turbo machines. 
     It should be appreciated that reference herein to only one of spike stall or spike stall precursor, or modal stall or modal stall precursor, refers to a magnitude or presence great enough such that the presence of the other of the stall conditions or precursors may be considered negligible. However, reference to a combination stall precursor refers to a magnitude or presence of both the spike stall precursors and the modal stall precursors such as to be considered non-negligible or considerable in regard to operation, or adjustments thereto, to compressor assembly or turbo machine operation. 
     Referring now to the figures,  FIG. 1  provides a schematic partially cross-sectioned side view of an exemplary turbo machine  10  herein referred to as “engine  10 ” as may incorporate various embodiments of the present invention. Various embodiments of the engine  10  may define a turbofan, turboshaft, turboprop, or turbojet gas turbine engine, including marine and industrial engines and auxiliary power units, or steam turbine engines, open rotor engines, or other apparatuses including compressor assemblies. As shown in  FIG. 1 , the engine  10  has a longitudinal or axial centerline axis  12  that extends therethrough for reference purposes. An axial direction A is extended co-directional to the axial centerline axis  12  for reference. A radial direction R is extended perpendicular to the centerline axis  12 . The engine  10  further defines an upstream end  99  and a downstream end  98  for reference. In general, the engine  10  may include a fan assembly  38  and a core engine  16  disposed downstream from the fan assembly  38 . 
     The core engine  16  may generally include a substantially tubular outer casing  18  that defines a core inlet  20  to a core flowpath  78 . The outer casing  18  encases or at least partially forms the core engine  16 . The outer casing  18  encases or at least partially forms, in serial flow relationship, a booster or low pressure (LP) compressor  22 , a high pressure (HP) compressor  24 , a combustion section  26 , a turbine section  31  including a high pressure (HP) turbine  28 , a low pressure (LP) turbine  30  and a jet exhaust nozzle section  32 . A high pressure (HP) rotor shaft  34  drivingly connects the HP turbine  28  to the HP compressor  24 . A low pressure (LP) rotor shaft  36  drivingly connects the LP turbine  30  to the LP compressor  22 . The LP rotor shaft  36  may also be connected to a fan shaft  42  of the fan assembly  38 . In particular embodiments, as shown in  FIGS. 2-4 , the LP rotor shaft  36  may be connected to the fan shaft  42  via a reduction gear  44  such as in an indirect-drive or geared-drive configuration. 
     As shown in  FIG. 1 , the fan assembly  38  includes a plurality of fan blades  40  that are coupled to and that extend radially outwardly from the fan shaft  42 . In certain embodiments, the fan assembly  38  includes one or more rows or stages of fan blades  40  longitudinally spaced apart from one another. An annular fan casing or nacelle  54  circumferentially surrounds the fan assembly  38  and/or at least a portion of the core engine  16 . It should be appreciated by those of ordinary skill in the art that the nacelle  54  may be configured to be supported relative to the core engine  16  by a plurality of circumferentially-spaced outlet guide vanes or struts  52 . Moreover, at least a portion of the nacelle  54  may extend over an outer portion of the core engine  16  so as to define a bypass airflow passage  56  therebetween. However, it should be appreciated that other embodiments of the engine  10  may define an open rotor assembly, in which one or more stages of the fan blades  40  are unshrouded by a nacelle. Certain embodiments of the engine  10  may partially or completely remove the nacelle. 
     It should be appreciated that combinations of the shaft  34 ,  36 ,  42 , the compressors  22 ,  24 ,  38  and the turbines  28 ,  30  define a rotor assembly  90  of the engine  10 . For example, the HP shaft  34 , HP compressor  24 , and HP turbine  28  may define an HP rotor assembly of the engine  10 . Similarly, combinations of the LP shaft  36 , LP compressor  22 , and LP turbine  30  may define an LP rotor assembly of the engine  10 . Various embodiments of the engine  10  may furthermore, or alternatively, include the fan shaft  42  and fan blades  40  as the LP rotor assembly. In other embodiments, the engine  10  may further define a fan rotor assembly at least partially mechanically de-coupled from the LP spool via the fan shaft  42  and the reduction gear  44 . Still other embodiments may further include one or more intermediate rotor assemblies defined by an intermediate pressure compressor, an intermediate pressure shaft, and an intermediate pressure turbine disposed between the LP rotor assembly and the HP rotor assembly relative to serial aerodynamic flow arrangement during normal operation. 
     It should be appreciated that, as used herein, various embodiments of a method for operating a compressor assembly (hereinafter, “method  1000 ”), a computer-implemented system for executing steps of the method  100  (hereinafter, “system  400 ”), the engine  10 , and/or a controller  210  shown and described herein may refer to the compressor assembly  21  as including one or more of a fan assembly (e.g., fan assembly  38 ) or one or more compressors (e.g., the LP compressor  22 , the HP compressor  24 , or one or more intermediate pressure compressors positioned between the LP compressor and the HP compressor), or combination thereof. Furthermore, it should be appreciated that embodiments of the method  1000 , the system  400 , or the controller  210  may be applicable to standalone compressor assemblies unattached to a combustor or turbine assembly. For instance, the compressor assembly may be driven by an external drive mechanism, load device, motor, or other motive device. 
     Various embodiments of the engine  10  may further include a mechanical load device or electric machine  92  electrically coupled to one or more rotor assemblies  90 , such as to generate, store, and/or distribute energy at the mechanical load device or electric machine  92  from and/or to the rotor assembly  90 . For example, the mechanical load device or electric machine  92  may be configured to extract energy from operation of the rotor assembly  90  such as to provide electrical energy to electrical systems of the engine  10  (e.g., the controller  210  further described herein), or aircraft or other apparatuses and sub-systems attached thereto. As yet another example, the mechanical load device or electric machine  92  may be configured drive the rotor assembly  90 , or particularly the compressor assembly  21 , to increase or decrease loading at the rotor assembly  90  such as to allow increased or decreased acceleration at the rotor assembly  90 , or particularly at the compressor assembly  21 , based at least on desired compressor loading, or changes therein, based on the method  1000  described herein for operating a compressor assembly to avoid spike stall and/or modal oscillations. 
     During operation of the engine  10 , a flow of air, shown schematically by arrows  58 , enters an inlet  60  of the engine  10  defined by the fan case or nacelle  54 . A portion of air, shown schematically by arrows  63 , enters the flowpath  78  at the core engine  16  through the core inlet  20  defined at least partially via the casing  18 . The flow of air  63  is increasingly compressed as it flows across successive stages of the compressors  22 ,  24 , such as shown schematically by arrows  64 . The compressed air  64  enters the combustion section  26  and mixes with a liquid or gaseous fuel and is ignited to produce combustion gases  66 . The combustion gases  66  release energy to drive rotation of the HP rotor assembly and the LP rotor assembly before exhausting from the jet exhaust nozzle section  32 . The release of energy from the combustion gases  66  further drives rotation of the fan assembly  38 , including the fan blades  40 . A portion of the air  62  bypasses the core engine  16  and flows across the bypass airflow passage  56 , such as shown schematically by arrows  62 . 
     Referring to  FIG. 1 , the engine  10  may further include a controller  210  configured to execute steps of the method  1000 . In certain embodiments, the controller  210  includes, at least in part, the system  400  further depicted and described herein. In various embodiments, the controller  210  can generally correspond to any suitable processor-based device, including one or more computing devices. For instance,  FIG. 1  illustrates one embodiment of suitable components that can be included within the controller  210 . As shown in  FIG. 1 , the controller  210  can include a processor  212  and associated memory  214  configured to perform a variety of computer-implemented functions. In various embodiments, the controller  210  may be configured to operate the engine  10  such as to determine an operating condition of the engine  10  corresponding to whether the compressor assembly  21  is operating in or toward a spike stall condition or a modal oscillation condition, such as further described herein. The controller  210  may further be configured to generate and transmit a control signal  218  corresponding to the determined operating condition. The controller  210  may still further be configured to operate the engine  10  based at least on the control signal  418 , such as to adjust a compressor loading of the compressor assembly  21 , such as adjusting fuel output to the combustion section  26 , adjusting variable vane angle at the compressor assembly  21  (e.g., at an inlet guide vane, variable stator vane, etc.), adjusting bleed air (e.g., via ports, valves, manifolds, pipes, doors, etc. at a bleed air assembly) from the compressor assembly  21  and/or combustion section  26 , or adjusting loading at the mechanical load device or electric machine  92  and rotor assembly  90  coupled together, or adjusting area of the jet exhaust nozzle  32 , etc. 
     As used herein, the term “processor” refers not only to integrated circuits referred to in the art as being included in a computer, but also refers to a controller, microcontroller, a microcomputer, a programmable logic controller (PLC), an application specific integrated circuit (ASIC), a Field Programmable Gate Array (FPGA), and other programmable circuits. Additionally, the memory  214  can generally include memory element(s) including, but not limited to, computer readable medium (e.g., random access memory (RAM)), computer readable non-volatile medium (e.g., flash memory), a compact disc-read only memory (CD-ROM), a magneto-optical disk (MOD), a digital versatile disc (DVD) and/or other suitable memory elements or combinations thereof. In various embodiments, the controller  210  may define one or more of a full authority digital engine controller (FADEC), a propeller control unit (PCU), an engine control unit (ECU), or an electronic engine control (EEC). 
     As shown, the controller  210  may include control logic  216  stored in memory  214 , such as shown and described in regard to the system  400  ( FIG. 5 ), or particularly the control logic  425  and/or control system  430 . The control logic  216  may include instructions that when executed by the one or more processors  212  cause the one or more processors  212  to perform operations, such as steps of the method  1000  for operating a compressor assembly. In still various embodiments, the memory  214  may store graphs or corresponding charts, tables, functions, look ups, etc. based thereon, such as described herein. 
     Additionally, as shown in  FIG. 1 , the controller  210  may also include a communications interface module  230 . In various embodiments, the communications interface module  230  can include associated electronic circuitry that is used to send and receive data. As such, the communications interface module  230  of the controller  210  can be used to receive data from one or more sensors  410  at the engine  10 , such as, but not limited to, rotational speed at the compressor assembly  21 , a rate of acceleration or deceleration, a change in rate of acceleration or deceleration, compressor loading, upstream and downstream compressor assembly pressure, inter-stage compressor assembly pressure, vibrations at the compressor assembly, temperature, pressure, and/or flow rate of fluid through the compressor assembly, temperature, pressure and/or flow rate of fuel to the combustion section  26 , etc. 
     In addition, the communications interface module  230  can also be used to communicate with any other suitable components of the engine  10 , the compressor assembly  21 , and/or system  400 , such as to receive data or send commands to/from any number of sensors, valves, vane assemblies, fuel systems, rotor assemblies, ports, etc. controlling speed, acceleration, temperature, pressure, or flow rate at the engine  10 . 
     It should be appreciated that the communications interface module  230  can be any combination of suitable wired and/or wireless communications interfaces and, thus, can be communicatively coupled to one or more components of the engine  10  via a wired and/or wireless connection. As such, the controller  210  may obtain, determine, store, generate, transmit, or operate any one or more steps of the method  1000  at the compressor assembly  21 , the engine  10 , an apparatus to which the engine  10  is attached (e.g., an aircraft), or a ground, air, or satellite-based apparatus in communication with the engine  10  (e.g., a distributed network). 
     In various embodiments, the sensors  410  at the engine  10  are positioned proximate to a blade tip  27  at a casing surrounding the compressor assembly  21  such as described herein. For example, the sensor  410  may include a pressure sensor or flow sensor positioned upstream and/or downstream of a rotating stage at the compressor assembly. As another example, the sensor  410  may be positioned proximate to or corresponding to one or more of a leading edge  23  or a trailing edge  25  of a blade of the compressor assembly  21 . 
     Referring now to  FIGS. 2-4 , flowcharts outlining exemplary steps of the method  1000  for operating a compressor assembly and turbo machine are provided. The method  1000  may improve compressor operability, performance, efficiency, and/or durability by more effectively determining, identifying, or classifying precursors to certain stall or surge conditions. In various embodiments, the determined stall precursor is used to generate one or more control signals or control responses for operating the compressor assembly and turbo machine to avoid or mitigate stall or surge. As further described herein, embodiments of the method  1000  may be implemented as instructions stored in and executed by controllers for turbo machines (e.g., controller  210 ) or other computer-implemented systems (e.g., system  400 ). 
     The method  1000  includes at  1005  initializing operation of the compressor assembly (i.e., rotating and pressurizing the compressor assembly) such as to at  1010  obtain a first data set over a first period of time and at  1020  obtain a second data set over a second period of time after the first period of time. The second data set refers to a subsequent data set relative to the first data set. The second data set is taken at least an integral or complete rotation subsequent to (e.g., after) one or more rotations over which the first data set is taken. Additionally, or alternatively, the first data set refers to some or all data sets preceding the second data set. For example, the first data set may include discrete data points, averages, running averages, etc. corresponding to one or more rotations of the compressor assembly over the first period of time preceding the one or more rotations over the second period of time. As another example, the first data set may include discrete data points, averages, or running averages, etc. of a plurality of data points (e.g., circumferential arrangement of sensors and/or axially arranged sensors across adjacent blade rows at the compressor section, etc.) from a plurality of sensors relative to a revolution of compressor blades. As such, in various embodiments, the first data set corresponds to one or more revolutions of the blades of the compressor assembly preceding one or more revolutions over which the second data set is obtained. 
     Similarly, the second data set may include discrete data points, averages, running averages, etc. corresponding to a plurality of data points from a plurality of sensors relative to one or more rotations of the compressor assembly subsequent to the first period of time. 
     In various embodiments, obtaining the first data set and the second data set includes obtaining data corresponding to one or more performance parameters of a fluid through the compressor assembly. In various embodiments, the fluid includes an oxidizer, such as air, flowing through a primary flowpath of the compressor assembly. In certain embodiments, the performance parameter includes a dynamic pressure measurement, a static pressure measurement, a fluid flow rate or velocity measurement, or changes thereof between one or more subsequent revolutions of the compressor assembly, or rates of change thereof between one or more subsequent revolutions of the compressor assembly, or combinations thereof. 
     Referring now to  FIG. 5 , a schematic flowchart depicting a computer-implemented system  400  (hereinafter, “system  400 ”) is provided. The system  400  is configured to perform one or more steps of the method  1000  such as outlined in  FIGS. 2-4 . In various embodiments, the system  400  includes a sensor  410  configured to measure, receive, calculate, or otherwise obtain a first data set  411  and a second data set  412  from a compressor assembly. In various embodiments, the first data set  411  and the second data set  412  are direct coupling (DC) signals received from the sensor  410 . In certain embodiments, the method  1000  includes comparing a non-high pass filtered first data set  411  and second data set  412 . Signals from the sensor  410  corresponding to the first data set  411  and the second data set  412 , such as received at steps  1010  and  1020 , respectively, are each free of filtering or normalization. As such, the signal received from the sensor  410 , such as corresponding to the method  1000  at steps  1010  and  1020 , are indicative of high frequency and low frequency components of the performance parameter versus time-dependent domain, such as depicted in graph  300  ( FIG. 4 ). 
     The system  400  receives and compares the first data set  411  and the second data  412  to determine a first correlation factor  413 , such as described in regard to the method  1000  at step  1032 . If the first correlation factor crosses, intersects, or otherwise exceeds a first threshold then a stall precursor exists. However, if the first correlation factor does not exceed the first threshold, a stall precursor is not present. The compressor assembly may continue to operate and the system  400  may continue to receive and compare the first data set  411  and the second data set  412  until the first threshold is exceeded, indicating that the stall precursor exists. 
     When the first correlation factor exceeds the first threshold, indicating that a stall precursor exists, the system  400  further filters the first data set  411  and the second data set  412 , such as at filter  415 . The filter  415  removes mean values from the first data set  411  and the second data set  412 , such as provided in the method  1000  at step  1040 . The filter  415  may generally define a DC to AC (capacitive coupling) filter or converter, or a high-pass filter. The filter  415  outputs the first data set and the second data set each removed of mean values (filtered first data set  421  and filtered second data set  422 , respectively) and a second correlation factor  414  is determined, such as described in regard to the method  1000  at step  1042 . The filtered data sets  421 ,  422  removed of mean values may generally correspond to low frequency signals or low frequency variation. The filtered data sets  421 ,  422  may further correspond to absolute values of the first and second data sets  411 ,  412 . The second correlation factor  414  may include comparing value magnitudes with respect to sign or relation to other values. As such, it should be appreciated that in various embodiments, the method  1000  at step  1040  may include comparing value magnitudes that include negative values. 
     The system  400  includes a control logic  425  configured to compare the first correlation factor and the second correlation factor to one or more thresholds such as described in regard to the method  1000  at step  1044 . The control logic  425  may further classify the stall precursor as either the spike stall precursor, the modal stall precursor, or the combination stall precursor, such as described in regard to the method  1000  at step  1046 . 
     Referring to  FIG. 6 , an exemplary graph  300  of the performance parameter over a time-dependent domain is provided. In the embodiment depicted in  FIG. 6 , the time-dependent domain is revolutions of a rotating stage of blades of a compressor assembly during operation. R2 defines one or more subsequent integral revolutions of the compressor assembly after R1. In various embodiments, the graph  300  depicts a performance parameter at a circumferential location of the compressor assembly corresponding to a rotating stage of blades. It should be appreciated that in other exemplary embodiments, the graph  300  may include a plurality of performance parameters corresponding to different circumferential locations at the rotating stage of blades. In still other embodiments, the graph  300  may compare a plurality of rotating stages. 
     Referring to  FIG. 6 , area  301  represents a first period of time over which a first data set is obtained, such as described in regard to step  1010  of the method  1000 . Area  302  represents a second period of time over which a second data set is obtained, such as described in regard to step  1020  of the method  1000 . Referring to  FIG. 7 , exemplary graph  310  depicts an overlay comparison of the first data set (depicted at  411 ) obtained at the first period of time (e.g., depicted at area  301  in  FIG. 6 ) and the second data set (depicted at  412 ) obtained at the second period of time (e.g., depicted at area  302  in  FIG. 6 ). 
     In various embodiments, obtaining the first and second data sets includes obtaining data at or near the blade tip at one or more axially adjacent blade rows of the compressor assembly. In another embodiment, obtaining data at the blade tip may include obtaining performance parameter measurements corresponding to a leading edge, a trailing edge, or a span therebetween, of the blade. In yet another embodiment, obtaining data at the blade tip may include positioning a sensor at or near a vane, stator, or casing immediately upstream or downstream, or both, of the rotating blade row. In still other embodiments, obtaining data may include a measurement from a sensor positioned at the rotating blade itself, such as via an electromechanical device configured to transmit power and electrical signals between static and rotary structures (e.g., a slip ring, a telemetry device, transmitter, etc.). 
     In still various embodiments, the method  1000  includes at  1007  measuring the performance parameter of the fluid at the compressor assembly, in which measuring the performance parameter generates a first data set and a second data set during a revolution of the compressor assembly after obtaining the first data set. In certain embodiments, measuring the performance parameter of the fluid includes measuring one or more of dynamic pressure, static pressure, flow rate, or velocity, or changes thereof between one or more subsequent revolutions of the compressor assembly, or rates of changes thereof between one or more subsequent revolutions of the compressor assembly, or combinations thereof. 
     Referring back to  FIGS. 2-4 , various embodiments of the method  1000  further includes at  1030  comparing the first data set and the second data set to determine a first correlation factor. The first correlation factor represents a degree by which the first data set and the second data set match one another. In various embodiments, the first correlation factor includes a signal matching algorithm or a cross-correlation function to process time-dependent signals. The time dependent signals may be based at least on the first data set and the second data set at one or more revolutions of the compressor assembly after or subsequent to the revolution(s) at which the first data set is obtained. The first correlation factor may be normalized to a scale of zero to one, or −1 to 1, or another appropriate scale. 
     The method  1000  further includes at  1032  comparing the first correlation factor to a first threshold. The first threshold at least partially determines whether a stall precursor exists. The first correlation factor equaling or exceeding the first threshold is indicative of a stall precursor existing at the compressor assembly. It should be appreciated that in various embodiments the first threshold may be a user input. The first threshold may be based at least on a known or desired limit relative to stall propagation at the compressor assembly. 
     The method  1000  at  1030  and  1032  determines whether a stall precursor exists during operation of the compressor assembly. Stall precursor includes the spike stall precursor, the modal stall precursor, or the combination stall precursor including the spike stall precursor and the modal stall precursor. At  1040 , the method  1000  further includes removing or filtering mean values from the first data set and the second data set obtained at steps  1010  and  1020 , respectively. At  1042 , the method  1000  includes comparing the first data set and the second data set each removed of mean values (i.e., the first data set and the second data set obtained from step  1040 ) to determine a second correlation factor different from the first correlation factor. At  1044 , the method  1000  includes comparing the second correlation factor to the first threshold. Comparing the second correlation factor to the first threshold at least partially determines whether the stall precursor determined at step  1030  is either the spike stall precursor, the modal stall precursor, or the combination stall precursor. The method  1000  at  1046  further classifies the stall precursor as either the spike stall precursor, the modal stall precursor, or the combination stall precursor based at least on comparing the second correlation factor to the first threshold. 
     In certain embodiments, the stall precursor is classified at step  1046  as the spike stall precursor if the first correlation factor exceeds the first threshold and the second correlation factor exceeds the first threshold. In still certain embodiments, the stall precursor is classified in step  1046  as the modal stall precursor if the first correlation factor exceeds the first threshold and the second correlation factor does not exceed the first threshold. 
     Referring now to  FIG. 8 ,  FIG. 9 , and  FIG. 10 , exemplary graphs are provided depicting steps of the method  1000  as may be performed by the system  400 .  FIGS. 8-10  depict graphs of a performance parameter correlation versus time-dependent domain (e.g., pressure comparison versus time). It should be appreciated that the time-dependent domain depicted in  FIG. 7  and  FIGS. 8-10  may represent instants of time. Each of graphs  601 ,  701 , and  801  depict a performance parameter correlation, such as the first correlation factor  413  determined from a comparison of the first data set  411  and the second data set  412  ( FIG. 7 ,  FIG. 5 ), and then compared to a first threshold  431 , such as described in regard to method  1000  at step  1032 . In each of graphs  601 ,  701 , and  801 , the first correlation factor  413  exceeds the first threshold  431  (e.g., crosses the first threshold  431 ). In each of graphs  602 ,  702 , and  802  a performance parameter correlation comparison of the second correlation factor  414  to the first threshold  431  is provided, such as described in regard to the method  1000  at step  1044 . In regard to graph  602  and graph  702  depicted in  FIGS. 8-9 , respectively, the second correlation factor  414  exceeds the first threshold  431 . In contrast, graph  802  in  FIG. 10  depicts the second correlation factor  414  not exceeding the first threshold  431 . In instances such as depicted in graph  802 , the control logic  425  classifies the stall precursor as the modal stall precursor indicative of the compressor assembly operating toward a modal stall condition. 
     Referring further to graphs  603 ,  703 , and  803  in  FIGS. 8-10 , respectively, overlays of the comparison of the first threshold  431  to each of the first correlation factor  413  and the second correlation factor  414  from graphs  601 ,  602 ,  701 ,  702 ,  801 , and  802  are provided respectively at graphs  603 ,  703 , and  803 . In various embodiments, the method  1000  and the system  400  compares magnitudes of the first correlation factor  413  and the second correlation factor  414  to further determine whether the stall precursor  416  is a spike stall precursor or a combination stall precursor. When the first correlation factor  413  and the second correlation factor  414  are substantially similar in magnitude, such as depicted in regard to graph  603 , the stall precursor is classified or identified as the spike stall precursor. 
     In contrast, when the first correlation factor  413  and the second correlation factor  414  differ in magnitude, such as depicted in regard to graph  703 , the stall precursor is classified or identified as the combination stall precursor. In various embodiments, the method  1000  includes at  1050  comparing the second correlation factor to a magnitude threshold, in which the magnitude threshold (e.g., magnitude threshold  433  in graph  703  in  FIG. 9 ) indicates whether the stall precursor is the combination stall precursor or the spike stall precursor. Referring to graph  703  in  FIG. 9 , a magnitude threshold  433  includes a magnitude difference in performance parameter correlation between the first correlation factor  413  and the second correlation factor  414 . In certain embodiments, the magnitude threshold  433  compares the first correlation factor  413  and the second correlation factor  414  at a time subsequent to the stall precursor  416 . 
     In still various embodiments, the method  1000  includes at  1046  classifying the stall precursor as one of either the combination stall precursor or the spike stall precursor based at least on the magnitude threshold  433 . The stall precursor is the combination stall precursor if the second correlation factor equals or exceeds the first threshold and the magnitude threshold (e.g., depicted in  FIG. 9 ). The stall precursor is classified as the spike stall precursor if the second correlation factor does not exceed magnitude threshold (e.g., depicted in  FIG. 8 ). 
     In various embodiments, a minimal degree of similarity, or alternatively, a maximal degree of dissimilarity (e.g., at or approaching 0 on a range of 0 to 1, or at or approach −1 on a range of −1 to 1, etc.) between the first correlation factor  413  and the second correlation factor  414  indicates a presence of both modal stall precursors and spike stall precursors such as to indicate the combination stall precursor classification (such as depicted in  FIG. 9  at graph  703 ) in contrast to the spike stall precursor classification (such as depicted in  FIG. 8  at graph  603 ). The magnitude threshold  433  may be indicative of a range at or over which the first correlation factor  413  and the second correlation factor  414  are dissimilar, although both the first correlation factor  413  and the second correlation factor  414  exceed the first threshold  431 . In  FIG. 10 , in contrast to  FIGS. 8-9 , although the first correlation factor  413  and the second correlation factor  414  are each dissimilar, only the first correlation factor  413  exceeds the first threshold  431 . As such, graph  803  in  FIG. 10  indicates the presence of only the modal stall precursor. 
     Differences between the spike stall precursor and the modal stall precursor may correspond to whether stall or surge conditions at the compressor assembly are developing at a blade tip or at a blade root or hub. Whether the stall or surge conditions are developing at the blade tip or at the blade root or hub further correspond to how an operating mode (e.g., rotational speed, acceleration, rate of acceleration, air and/or fuel flow rate, etc.) of the turbo machine may be adjusted to mitigate stall or surge at the compressor assembly. 
     In still various embodiments, the two or more steps of the method  1000  are in sequential order such as to determine whether the compressor assembly is operating with a stall precursor condition, and then to determine whether the stall precursor condition is specifically either the spike stall precursor, the modal stall precursor, or the combination spike and modal stall precursor. In one embodiment, the method  1000  at  1030  immediately precedes the step  1032 . In another embodiment, the method  1000  at  1040  immediately precedes the method  1000  at steps  1042 ,  1044 , and  1046 . 
     In various embodiments, the magnitude threshold  433  may be based at least on a known or desired limit relative to stall propagation at the compressor assembly. In one embodiment, the magnitude threshold  433  defines an approximately 33% or less difference in magnitude between the first correlation factor  413  and the second correlation factor  414 . In another embodiment, the magnitude threshold  433  defines an approximately 25% difference in magnitude between the first correlation factor  413  and the second correlation factor  414 . In yet another embodiment, the magnitude threshold  433  defines an approximately 20% difference in magnitude between the first correlation factor  413  and the second correlation factor  414 . In still another embodiment, the magnitude threshold  433  defines an approximately 10% difference in magnitude between the first correlation factor  413  and the second correlation factor  414 . In still yet another embodiment, the magnitude threshold  433  defines an approximately 5% or greater difference in magnitude between the first correlation factor  413  and the second correlation factor  414 . In various embodiments, the first correlation factor  413  and the second correlation factor  414  are substantially equal in magnitude if the magnitude difference is less than approximately 5%. 
     It should be appreciated that embodiments of the method  1000  implemented at a turbo machine, or in various embodiments of the system  400  or controller  210  shown and described herein, one or more of the first threshold, the second threshold, and/or the magnitude threshold described herein may vary based at least on an apparatus or desired operating condition of the turbo machine. For example, thresholds, or magnitudes thereof, associated with a fan assembly, a low pressure (LP) compressor, an intermediate pressure (IP) compressor, or a high pressure (HP) compressor may vary substantially relative to one another. Additionally, or alternatively, thresholds, or magnitudes thereof, may vary substantially across stages of compression within one of the fan assembly, the LP compressor, the IP compressor, or the HP compressor. It should therefore be appreciated that the threshold, or magnitudes thereof, may vary based at least on a desired airflow rate, pressure, pressure ratio, temperature, quantity of stages or compression, rate and/or percentage of bleed airflow, rate and/or percentage of bypass airflow, or other airflow control mechanism. 
     Referring back to  FIG. 5 , various embodiments of the system  400  further outputs  417  from the control logic  425  the classification of the stall precursor as either the spike stall precursor, the modal stall precursor, or the combination stall precursor. A control system  430  receives the output signal  417  from the control logic  425 . 
     Referring back to  FIGS. 2-4 , in various embodiments the method  1000  may further include at  1060  generating a control signal based on whether the stall precursor is classified as one of the spike stall precursor, the modal stall precursor, or the combination stall precursor. In certain embodiments, generating the control signal at  1060  includes adjusting a desired performance parameter at the turbo machine based at least on the identified or classified type of stall precursor. Referring to  FIG. 5 , the control system  430  may generate and output a control signal  418  to a controller configured to operate one or more of a desired compressor loading separate, different, or unique from one another. The changes in compressor loading include, but is not limited to, changes in fuel output to the combustion section (e.g., changes in fuel flow or pressure), changes in variable vane angle (e.g., at an inlet guide vane, variable stator vane, etc.), or changes in bleed air (e.g., at an upstream compressor bleed, at one or more inter-stage compressor bleeds, at a downstream bleed, such as at the combustion section, at a variable vane door at or between one or more compressors  22 ,  24  in  FIG. 1 , etc.), varying a 3 rd  stream air flow path, or varying an exhaust nozzle area, etc. In still various embodiments, the rotor assembly to which the compressor assembly is attached may further include a mechanical load device or an electric machine configured to adjust loading applied to the compressor assembly, such as to provide changes in rate of acceleration of the compressor assembly. 
     In certain embodiments, the method  1000  further includes adjusting a performance parameter at the compressor assembly based at least on the control signal generated at  1060 . Adjusting the performance parameter is based at least on the stall precursor being classified as one of the spike stall precursor, the modal stall precursor, or the combination stall precursor, such as described in regard to step  1046 . 
     Adjusting the performance parameter may be based at least on a control response generated based on the control signal. In various embodiments, the method  1000  includes at  1062  generating a first control response based at least on stall or surge conditions developing at the blade tip, such as corresponding to the stall precursor classified as the spike stall precursor. In another embodiment, the method  1000  at  1060  further includes at  1064  generating a second control response based at least on stall or surge conditions developing at the blade root or hub, such as corresponding to the modal stall precursor. In still another embodiment, the method  1000  includes at  1066  generating a third control response based at least on stall or surge conditions developing at both of the blade tip and the blade root or hub, such as corresponding to both of the spike stall precursor and the modal stall precursor (i.e., the combination stall precursor). 
     In various embodiments, the method  1000  further includes at  1070  operating the turbo machine based at least on the generated control signal at  1060 , and/or one or more of the control responses at  1062 ,  1064 , or  1066 . In still various embodiments, such as described above, the method  1000  at  1070  includes at  1072  adjusting a compressor loading at the compressor assembly. 
     Referring back to  FIG. 4 , in certain embodiments, the method  1000  further includes at  1072  adjusting a compressor loading at the compressor assembly based at least on a classification of the stall precursor as one of the spike stall precursor, the modal stall precursor, or the combination stall precursor, such as described in regard to step  1046 . In another embodiment, the method  1000  further includes at  1074  adjusting the performance parameter at the compressor assembly based at least on the classification of the stall precursor such as described in regard to step  1046 . In some embodiments, adjusting the compressor loading at  1072  or adjusting the performance parameter includes reducing fuel flow to the combustion section, increasing mechanical load device or electric machine loading onto a rotor assembly including the compressor assembly, or actuating (i.e., opening or closing) one or more bleed valves or ports of a bleed air assembly based at least on the generated control signal (such as described in regard to step  1060 ) or the generated control response (such as described in regard to step  1062 ,  1064 , or  1066 ). 
     Referring now to  FIG. 11 , in some embodiments, the method  1000  may include comparing the second correlation factor to a second threshold (e.g., second threshold  432  depicted in  FIG. 11 ) different from the first threshold (e.g., first threshold  431 ). In certain embodiments, if the first correlation factor  413  crosses the first threshold  431  and the second threshold  432 , and the second correlation factor  414  crosses the first threshold  431  but does not cross the second threshold  432 , the stall precursor is classified at step  1046  as the combination stall precursor, such as depicted in regard to graph  901  in  FIG. 11 . If the first correlation factor  413  crosses the first threshold  431  and the second threshold  432 , and the second correlation factor  414  crosses both the first threshold  431  and the second threshold  432 , the stall precursor is classified as the spike stall precursor. If the first correlation factor crosses the first threshold  431  and the second threshold  432 , and the second correlation factor  414  does not cross the first threshold  431  and the second threshold  432 , the stall precursor is classified as the modal stall precursor, such as depicted in part in graph  802  in  FIG. 10 . 
     It should be appreciated that a difference in magnitude between the first threshold  431  and the second threshold  432  may alternatively be represented by the magnitude threshold  433 , such as depicted and described in regard to  FIG. 9 . 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. 
     Further aspects of the invention are provided by the subject matter of the following clauses: 
     1. A computer-implemented method for operating a compressor assembly, the method comprising obtaining a first data set over a first period of time, obtaining a second data set over a second period of time after the first period of time, comparing the first data set and the second data set to determine a first correlation factor, comparing the first correlation factor to a first threshold, wherein the first threshold at least partially determines whether a stall precursor exists, removing mean values from the first data set and the second data set, comparing the first data set and the second data set each removed of mean values to determine a second correlation factor, comparing the second correlation factor to the first threshold, wherein comparing the second correlation factor to the first threshold at least partially determines whether the stall precursor comprises one of a spike stall precursor, a modal stall precursor, or a combination stall precursor, and classifying the stall precursor as either the spike stall precursor, the modal stall precursor, or the combination stall precursor. 
     2. The computer-implemented method of any preceding clause, wherein the stall precursor is classified as one of the spike stall precursor or the combination stall precursor if the first correlation factor exceeds the first threshold and the second correlation factor exceeds the first threshold, and wherein the stall precursor is classified as the modal stall precursor if the first correlation factor exceeds the first threshold and the second correlation factor does not exceed the first threshold. 
     3. The computer-implemented method of any preceding clause, the method including generating a control signal based on whether the stall precursor is classified as one of the spike stall precursor, the modal stall precursor, or the combination precursor. 
     4. The computer-implemented method of any preceding clause, including adjusting a performance parameter at the compressor assembly based at least on the control signal, wherein adjusting the performance parameter is based at least on the stall precursor being classified as one of the spike stall precursor, the modal stall precursor, or the combination stall precursor. 
     5. The computer-implemented method of any preceding clause, including comparing the second correlation factor to a magnitude threshold indicative of the stall precursor being classified as either the combination stall precursor or the spike stall precursor. 
     6. The computer-implemented method of any preceding clause, including classifying the stall precursor as one of either the combination stall precursor or the spike stall precursor, wherein the stall precursor is the combination stall precursor if the second correlation factor exceeds the first threshold and the magnitude threshold, and wherein the stall precursor is the spike stall precursor if the second correlation factor does not exceed magnitude threshold. 
     7. The computer-implemented method of any preceding clause, wherein removing mean values from the first data set and the second data set comprises converting the first data set and the second data set from a direct current signal to an alternating current signal. 
     8. The computer-implemented method of any preceding clause, wherein obtaining the second data set over a second period of time is during a revolution of the compressor assembly after obtaining the first data set. 
     9. A computing system for operating a turbo machine, the computing system configured to perform operations, the operations including the method of any preceding clause. 
     10. The computing system of any preceding clause, the operations including obtaining a first data set over a first period of time, obtaining a second data set over a second period of time after the first period of time, wherein the second period of time is during a revolution of the turbo machine after obtaining the first data set over the first period of time, identifying whether a stall precursor exists at the turbo machine, identifying a type of stall precursor, wherein the type of stall precursor comprises one of a spike stall precursor, a modal stall precursor, or a combination stall precursor. Identifying the type of stall precursor includes the method of any preceding clause. 
     11. The computing system of any preceding clause, the operations including comparing the first data set and the second data set to provide a first correlation factor, removing mean values from the first data set and the second data set, determining a second correlation factor by comparing the first data set and the second data set each removed of mean values, and comparing the second correlation factor to a first threshold, and generating a control signal based at least on the identified type of stall precursor. 
     12. The computing system of any preceding clause, wherein the type of stall precursor is identified as the modal stall precursor if the first correlation factor exceeds the first threshold and the second correlation factor does not exceed the first threshold. 
     13. The computing system of any preceding clause, wherein the type of stall precursor is identified as one of the spike stall precursor or the combination stall precursor if the first correlation factor exceeds the first threshold and the second correlation factor exceeds the first threshold. 
     14. The computing system of any preceding clause, wherein the type of stall precursor is identified as the combination stall precursor if the second correlation factor exceeds the first threshold and a magnitude threshold, wherein the magnitude threshold is a predetermined difference in magnitude between the first correlation factor and the second correlation factor. 
     15. The computing system of any preceding clause, the operations including generating a first control response based at least on the control signal, wherein the first control response corresponds to the spike stall precursor, and wherein the spike stall precursor is indicative of a stall condition or a surge condition at the turbo machine. 
     16. The computing system of any preceding clause, the operations including generating a second control response based at least on the control signal, wherein the second control response corresponds to the modal stall precursor. 
     17. The computing system of any preceding clause, the operations including comparing the second correlation factor to a second threshold different from the first threshold, wherein the type of stall precursor is identified as the combination stall precursor if the first correlation factor exceeds the first threshold and the second correlation factor does not exceed the second threshold, wherein the type of stall precursor is identified as the spike stall precursor if the first correlation factor exceeds the first threshold and the second correlation factor exceeds the second threshold, and wherein the type of stall precursor is identified as the modal stall precursor if the second correlation factor does not exceed the first threshold. 
     18. A turbo machine including the computing system of any preceding clause. 
     19. A turbo machine configured to execute the computer-implemented method of any preceding clause. 
     20. A turbo machine of any preceding clause, the turbo machine including a compressor assembly, wherein the compressor assembly includes a sensor positioned at adjacent stages of compressor blade rows, wherein the sensor is configured to obtain a performance parameter of a fluid through the compressor assembly. 
     21. The turbo machine of any preceding clause, the turbo machine including a controller including a processor and memory configured to store instructions that, when executed by the processor, causes the processor to perform operations, the operations including the operations of the computer system of any preceding clause and/or the steps of the method of any preceding clause. 
     22. The turbo machine of any preceding clause, the operations including obtaining, via the sensor, a first data set over a first period of time during rotation of the compressor assembly, and obtaining, via the sensor, a second data set over a second period of time following the first period of time, wherein the second period of time corresponds to one or more revolutions of the compressor assembly after the first period of time. 
     23. The turbo machine of any preceding clause, the operations including comparing the first data set and the second data set to determine a first correlation factor, removing mean values of the first data set and the second data set, determining a second correlation factor by comparing the first data set and the second data set each removed of mean values, and determining a type of stall precursor at the compressor assembly, wherein determining the type of stall precursor is based at least on comparing the first correlation factor to a first threshold and comparing the second correlation factor to a magnitude threshold, and wherein the type of stall precursor is one of a spike stall precursor, a modal stall precursor, or a combination stall precursor, and operating the compressor assembly based at least on the determined type of stall precursor. 
     24. The turbo machine of any preceding clause, the operations including adjusting the performance parameter at the compressor assembly based at least on the stall precursor being one of the spike stall precursor, the modal stall precursor, or the combination stall precursor. 
     25. The turbo machine of any preceding clause, the operations including generating a control signal based at least on the type of stall precursor determined at the compressor assembly, wherein operating the compressor assembly is based at least on the generated control signal. 
     26. The turbo machine of any preceding clause, the operations including measuring the performance parameter of the fluid at the compressor assembly, wherein measuring the performance parameter generates the first data set and the second data set. 
     27. The turbo machine of any preceding clause, wherein measuring the performance parameter of the fluid comprises measuring one or more of dynamic pressure, static pressure, flow rate, or velocity, or changes thereof between one or more subsequent revolutions of the compressor assembly, or rates of changes thereof between one or more subsequent revolutions of the compressor assembly, or combinations thereof. 
     28. The turbo machine of any preceding clause, the controller including a communications interface module configured to receive data from the sensor, the data including rotational speed at the compressor assembly, a rate of acceleration or deceleration at the compressor assembly, a change in rate of acceleration or deceleration at the compressor assembly, compressor loading, upstream and downstream compressor assembly pressure, inter-stage compressor assembly pressure, vibrations at the compressor assembly, temperature, pressure, and/or flow rate of fluid through the compressor assembly, temperature, pressure and/or flow rate of fuel to a combustion section, or combinations thereof. 
     29. The turbo machine of any preceding clause, the communications interface module configured to receive data and/or send commands to/from a valve, a vane assembly, a fuel system, a rotor assembly, and/or a port at a compressor assembly configured to control one or more of speed, acceleration, temperature, pressure, or flow rate of fluid through the compressor assembly and/or fuel at the combustion section. 
     30. The turbo machine of any preceding clause, the controller including a control logic including instructions that when executed by the processor causes the processor to perform operations of any preceding clause. 
     31. The computing system of any preceding clause, the computing system configured to perform operations of any preceding clause. 
     32. The computer implemented method of any preceding clause, the method including operations of any preceding clause.