METHOD FOR DETERMINING A TEMPERATURE FIELD ON A PART, SYSTEM AND ASSOCIATED AIRCRAFT ENGINE NACELLE

Abstract

The invention relates to a method for determining (300) a temperature field of a part (102), said method comprising the following steps: measuring (306) temperatures (Tm) on said part (102) by means of a network of N temperature sensors (104), where N is a natural integer strictly greater than unity, said temperature sensors (104) being fixed on or in the part (102); from a reference thermal source (S), determining (304) a set of simulated temperatures (Ts) on said part (102) by applying a direct model (M) of thermal conduction with a mesh (500) of the part (102) according to a finite element technique, said mesh (500) comprising a plurality of meshes (502); define the position of each temperature sensor within the mesh; for each of the meshes (502), correlate (308) the temperature values ​​(Tm) measured in step a) with a simulated temperature value (Ts) obtained at the end of step b).Figure for abstract: Fig. 3.

Description

Title of the invention: METHOD FOR DETERMINING A TEMPERATURE FIELD ON A PART, ASSOCIATED SYSTEM AND AIRCRAFT ENGINE NACELLE Technical field of the invention

[0001] The present invention lies in the field of thermal protection, in particular for aeronautical applications.

[0002] The present invention relates more specifically to a method for determining a temperature field of a part, for example a thermal protection panel, a computer program, a system and an associated aircraft engine nacelle.

[0003] It finds a preferred application for quantifying the effectiveness of thermal protection, such as a thermal protection panel arranged around an aircraft engine. In this context, the method of the present invention can be applied to a thermal protection panel during the production phase of said thermal protection panel, and therefore during a test phase, or even in use during a flight phase of the aircraft.

[0004] The invention also finds an application for the real-time identification of anomalies or thermal events likely to occur in aircraft engines. Technological background

[0005] Document CN115356372 describes a method ([Fig.3]) for evaluating the temporal thermal response of thermal protection of an aircraft made of composite material, in particular for testing new materials.

[0006] More particularly, document CN115356372 aims to determine the temperature distribution of the material subjected to hypersonic flight conditions. The temperatures are measured (S 101) at a first instant on a control surface and the heat flow data of the test surface made of the new material are determined. Thus, this document aims to determine thermodynamic coefficients in order to characterize the behavior of the new material and not to construct a temperature field on a part. In this regard, a temperature sensor is installed in a cavity formed in the control surface. The flows of the emitted (radiation) and dissipated (dissipation) heat are calculated according to the Stefan-Boltzmann law (S 102). The aerodynamic heat flow is determined (S 103). The complete temperature field of the test surface is determined (S 107). The different steps for obtaining a map are not described therein.

[0007] This method operates within the framework of an analysis of the inverse problem of conduction heat and aims more specifically to correct the uncertainties obtained during the inversion of the data.

[0008] It may thus be desirable to provide a part which makes it possible to overcome at least some of the aforementioned problems and constraints. Summary of the invention

[0009] According to the invention, it is proposed to determine, iteratively, a reference thermal excitation source which, when applied to a direct model of thermal propagation of the part, provides simulated temperatures close to the temperatures measured on the part and to deduce therefrom a temperature map of the part by applying the determined reference thermal source to the direct model. Advantageously, the measured temperatures are provided for a limited number of locations on the part while the simulated temperatures are estimated in a quasi-continuous manner on the part (i.e. a much higher number of points than for the measured temperatures).

[0010] A method is therefore proposed for determining a temperature field of a part comprising at least one surface subjected to a thermal source, said method comprising the following steps: a. measuring temperatures on said part by means of a network of N temperature sensors, where N is a natural integer strictly greater than unity, said temperature sensors being fixed on or in the part, according to a predetermined position, at a non-zero distance from the surface of the part; b. from a reference thermal source, determining a set of simulated temperatures within said part by applying a direct thermal conduction model with a mesh of the part according to a finite element technique, said mesh comprising a plurality of meshes; c. define the position of each temperature sensor within the mesh; d. for each of the meshes, correlate the temperature values ​​measured in step a) with a simulated temperature value obtained at the end of step b); e. as long as a predefined stopping condition is not met at the end of step c), modify the reference thermal source and then repeat steps d) and e) with the reference thermal source thus modified; f. once the stop condition is met, store the set of simulated temperatures (Ts) determined during the last implementation of step b) as a room temperature field.

[0011] Thus, the invention makes it possible to reconstruct the reference thermal source from the temperature field of the part. Indeed, the simulated temperatures, that is to say the temperatures obtained at the output of the direct thermal conduction model, are iterated tively compared to the temperatures measured on the part in order to adjust the reference thermal source. In this way, it is possible to reconstruct a thermal excitation source and deduce a temperature map over the entire part from localized measurements.

[0012] The invention may further comprise one or more of the following optional features, in any technically possible combination:

[0013] the reference thermal source is defined by at least one thermal source function representative of a temperature distribution around a reference point corresponding to a position of the reference thermal source on the part, said function being defined by at least one of the following parameters: a maximum amplitude at the reference point, a width at half-height;

[0014] step d) comprises adjusting at least one of the following parameters of said at least one thermal source function: position, amplitude, height at mid-height, type(s) of function;

[0015] said at least one function of the reference thermal source is of Lo-rentzian or Gaussian type;

[0016] the reference thermal source is defined by a combination, preferably linear, of at least two thermal source functions;

[0017] the reference thermal source is defined by a combination of at least two thermal source functions of different type;

[0018] the method comprises a prior step of obtaining said direct model from at least one heat propagation equation defined as a function of the following physico-thermal parameters of the part: thermal conductivity, specific heat, density;

[0019] the direct model is validated as a function of temperatures measured on said part in response to a thermal excitation corresponding to a thermal calibration source used to establish the direct model.

[0020] The invention also relates to a computer program downloadable from a communications network and / or recorded on a computer-readable medium, characterized in that it comprises instructions for executing the steps of a method for determining a temperature field as described above, when said program is executed on a computer.

[0021] The invention further relates to a system for determining a temperature field of a room comprising at least one surface subjected to a thermal source, said device comprising:

[0022] - a network of temperature sensors for measuring temperatures on said part, said temperature sensors being intended to be fixed on or in the part, according to a predetermined position, at a non-zero distance from the surface of the room; and

[0023] - calculation means connected to the temperature sensor network (104), the means calculation being configured to implement steps b) to e) of the method for determining the temperature field as previously described.

[0024] The invention may further comprise one or more of the following optional features, in any technically possible combination:

[0025] the system further comprises the part;

[0026] the system comprises at least one aircraft part, located side by side with the part.

[0027] The invention also relates to the use of a system for determining the thermal stress on said aircraft part.

[0028] The invention finally relates to an aircraft engine nacelle comprising a system as previously described. Brief description of the figures

[0029] The invention will be better understood with the aid of the following description, given solely by way of example and with reference to the appended drawings in which: - [Fig. 1a] schematically illustrates a system for determining a temperature field on a thermal protection panel according to an embodiment of the invention; - [Fig. 1b] schematically illustrates a system for determining a temperature field on a thermal protection panel according to a second embodiment of the invention; - [Fig.2] schematically illustrates an electronic control unit integrated into the system of figures 1a and 1b; - [Fig.3] schematically illustrates a method for determining a temperature field using the system of figures 1a and 1b; - [Fig.4] schematically illustrates an example of a method for determining a direct model representative of a thermal behavior of the thermal protection panel; and - [Fig.5] is a three-dimensional representation of a part of an aircraft engine nacelle in which the system of figures 1a and 1b is installed. Detailed description of the invention

[0030] With reference to Figures 1a and 1b, a system 100 for determining a temperature field according to a particular embodiment will now be described.

[0031] The system 100 comprises a network of N temperature sensors 104, where N is a natural integer strictly greater than unity. Thus, for simplicity, only four sensors 104 have been shown but in practice this number can be adjusted freely, for example depending on the size of the system or the intended application. The position of these sensors can be chosen based on either the thermophysical properties of a part 102 or experimental data on the most common positions for detecting thermal anomalies. The thermophysical properties in question are, for example, the density, the specific heat or the thermal conductivity of the part 102.

[0032] According to a particular embodiment, each temperature sensor 104 is a K-type “thermocouple”. Alternatively, the temperature sensor is a printed temperature sensor of the type used in printed electronics. In a known manner, a thermocouple comprises two metal wires of different natures (e.g. different metal) and connected together at a common end called a hot junction (or “hot junction”). When this common end is subjected to a thermal source, a potential difference (or voltage) appears between the free ends of the two metal wires, commonly called cold junctions (or “cold junction”). This potential difference, essentially due to the Seebeck effect, is representative of the quantity of heat applied to the hot junction and thus makes it possible to determine the temperature precisely at this point.

[0033] The system 100 according to the invention further comprises the part 102. The part comprises at least one surface subjected to a thermal source. Thus, it presents a surface or volume evolution of its temperature, an evolution for which it is desired to map it. According to the embodiments, the part 102 may be a thermal protection panel 102 for which it is desired to obtain a temperature map making it possible to show how the temperature is distributed across this panel.

[0034] In the present embodiment, the thermal protection panel 102 is adapted to thermally insulate an aircraft engine.

[0035] In the illustrated example, the thermal protection panel 102 comprises three layers of materials 102a, 102b, 102c. The three layers may be made of the same material, or two of the three layers of material may be made of the same material. The three layers may be made of one or more insulating materials, or only two of the three layers may be made of one or more insulating materials, or only one of the three layers may be made of one insulating material. Thus, the number of layers of insulating material is not limiting. In practice, the part 102 may have a number of layers of at least one. Even in the case where the part 102 comprises only one layer, the temperature field to be determined may be surface or volumetric. As indicated previously, the number of layers is not limiting within the scope of the invention.

[0036] Let us return to the embodiment in which the thermal protection panel comprises three layers. The panel 102 comprises a first metal wall 102a, a second metal wall 102b and an intermediate layer 102c of thermal insulation material called “insulator” included between the first and second metal walls 102a, 102b. It should be noted that the layer 102a may be a metal foil or an insulator even if it is placed on the side of the thermal source. The layer 102b may be a metal foil or an insulator even if it is the layer furthest from the thermal source, for example a heat source. In this regard, the thermal source may indifferently be located outside the thermal protection panel on the side of any one of the layers 102a, 102b. In this case, the surface of the part subjected to the thermal source is an external surface of the thermal protection panel.

[0037] In the case of a part 102, such as a pipe, it could also be placed inside the pipe near any of the layers 102a, 102b, 102c. Such a pipe may for example transport a hot fluid and it may then be useful to determine the temperature field around the pipe. In this case, the heat source is the hot fluid and the surface of the part which is subjected to the heat source is an interior surface of the pipe.

[0038] For example, each metal wall 102a, 102b is a metal sheet, preferably stainless steel. A stainless steel sheet is typically 50 micrometers thick.

[0039] Thus, the two metal walls 102a, 102b can each constitute a layer of thermally insulating material known as radiation, in the sense that the metal of which they are made radiates thermally by reflecting at their surface part of the heat incident on the panel 102.

[0040] The intermediate layer 102c is thermally insulating in transmission, in the sense that the insulating material of which it is made has a thermal resistance greater than that of the other two layers 102a, 102b.

[0041] In the example illustrated in [Fig.1a], the panel 102 comprises a first interface 102ca between the first metal wall 102a (first layer) and the intermediate layer 102c and a second interface 102cb between the second metal wall 102b (second layer) and the intermediate layer 102c.

[0042] Generally, when the thermal source is located outside the part 102 for which the mapping is to be carried out, it is preferable that each temperature sensor 104 is fixed, preferably welded, on at least one interface between two layers of the panel 102. In the present example, the temperature sensors 104 are all fixed on the first interface 102ca between the first metal wall 102a and the intermediate layer 102c, so that the N temperature sensors 104 are buried in the insulating material of the intermediate layer 102c. In the present embodiment, it is assumed that the interface 102ca on which the temperature sensors 104 are fixed is the one which is closest to a thermal source, like an airplane engine.

[0043] In alternative embodiments (not shown), the temperature sensors 104 may all be fixed to the second interface 102cb, i.e. between the second metal wall 102b and the intermediate layer 102c, assuming that the thermal source (e.g. aircraft engine) is arranged on the side of the first metal wall 102a. Alternatively, the temperature sensors may be distributed over the first 102ca and second 102cb interfaces. In all cases, the N temperature sensors 104 are advantageously arranged inside the thermal protection panel 102.

[0044] Still in the case where the thermal source is located outside the room 102 for which the mapping is to be carried out, the sensors could also be fixed on the wall furthest from the thermal source. Indeed, it should be recalled that since the invention aims to determine the temperature field of a room 102, it is appropriate to maintain a distance, at least non-zero, between the temperature sensors and the location of the thermal source, otherwise the interest in carrying out mapping would be limited. Thus, if the thermal source is located outside the part 102 on the side of the layer 102a, the temperature sensors 104 could be fixed on the layer 102b, inside or outside the part 102. Similarly, if the thermal source is located outside the part 102 on the side of the layer 102b, the temperature sensors 104 could be fixed on the layer 102b, inside or outside the part 102.[Fig.lb] illustrates this last example of realization.

[0045] Of course, in the case where the thermal source is located inside the part 102 for which the mapping is to be carried out, for example a pipe, the sensors are preferably fixed on the wall furthest from the thermal source on an external surface of the part 102, which makes it possible to maintain a distance between the temperature sensors and the location of the thermal source.

[0046] According to one aspect of the invention, regardless of the layer 102a, 102b, 102c, the interface 102ca, 102cb to which the temperature sensors 104 are fixed, their positioning is predetermined. In other words, the position of each temperature sensor 104 within the thermal protection panel 102 is known so that the relative position of the temperature sensors 104 with respect to each other and as described below, with respect to the meshes 502 of the panel, can be determined.

[0047] The system according to the invention 100 further comprises an electronic control unit 110, from the English “Electronic Control Unit” (ECU) commonly used in the aeronautical (or automotive) field.

[0048] Each temperature sensor 104 is connected to the electronic control unit 110, for example, by means of a dedicated electrical harness 106.

[0049] An embodiment of the electronic control unit 110 called “mode "embedded" will now be described with reference to [Fig.2].

[0050] According to this on-board mode, the electronic control unit 110 comprises a first electronic card 200 called the temperature data acquisition and transmission card and a second electronic card 210 called the power and communication card.

[0051] The first 200 and second 210 electronic cards are connected to each other by a communication bus 208, forming a link adapted for example to the RS-485 communication standard.

[0052] For example, the first electronic card 200 comprises a main computer 202, a non-volatile memory 204 and a communication interface 206. In the present embodiment, the main computer 202 is a microcontroller. Preferably, the communication interface 206 is configured to receive and / or transmit digital data according to the RS-485 standard.

[0053] In particular, the first electronic card 200 is configured to receive, for example at regular time intervals, electrical voltages supplied to the terminals of the temperature sensors 104 and transmitted by the electrical harnesses 106 at the level of input / output ports 200.1-200.4 of said card 200.

[0054] The first electronic card 200 is configured to determine, from received voltages, measured temperatures and store them in the non-volatile memory 204.

[0055] For example, the first electronic card 200 is configured to amplify and / or filter the electrical voltages provided by the temperature sensors 104, converting these voltages into digital form.

[0056] In the present embodiment, the second electronic card 210 comprises a microprocessor 212, a power module 214, a communication interface 216 and a memory 218, for example of the ROM (“Read Only Memory”) type.

[0057] The power module 214 is configured to power the first electronic card 200, for example by means of a power cable 209. For example, the power module 214 comprises a voltage converter for converting a voltage from a primary electrical source (not shown) into a nominal voltage (eg 28 V for applications in the aeronautical field).

[0058] The communication interface 216 is adapted to receive the temperature data obtained by the first electronic card 200 and transmitted on the communication bus 208, for example according to the RS-485 standard.

[0059] The microprocessor 212 is configured to implement a method according to the invention in the form of a computer program P which is for example stored in the memory 218. This method will be described later with reference to [Fig.3].

[0060] One of the main advantages of the present embedded embodiment is that the network of N temperature sensors 104 and the electronic cards 200, 210 are integrated into the thermal protection panel 102 to be thermally characterized, so that the panel is autonomous to determine itself a temperature field on the panel 102, from the temperatures measured by the network of N temperature sensors 104.

[0061] In an alternative embodiment called “remote” (not shown), the second electronic card 210 is arranged outside the thermal protection panel 102, so as to benefit from a less restricted footprint than in the on-board mode. Thus, the second remote electronic card 210 can advantageously be placed in a space of the aircraft that is less constrained than the panel 102 in terms of footprint.

[0062] In the case where the panel 102 is located at a source of high heat, such as an engine operating at full speed for a long period, the remote mode is particularly advantageous for preventing the second electronic card 210 from being subjected to excessively high temperatures, so as to preserve the electronic components of the electronic card 210, in particular the microprocessor 212, and / or limit the cooling or ventilation requirements of the electronic card 210.

[0063] Generally, the first electronic card 200 and / or the second electronic card 210 can be protected by a specific insulating coating, whether the card is arranged inside or outside the panel 102.

[0064] A method 300 for determining a temperature field of the thermal protection panel 102 implemented by the system 100 will now be described with reference to [Fig.3].

[0065] The method 300 comprises a prior step 302 of obtaining a digital thermal propagation model called a “direct model” M, making it possible to determine a set of simulated temperatures within the thermal protection panel 102, in response to the application of a reference thermal source to said panel.

[0066] Preferably, the direct model M is defined from at least one heat propagation equation defined as a function of physico-thermal parameters of the thermal protection panel 102: the thermal conductivity X, the specific heat Cp, the density p and boundary conditions CL of the thermal protection panel 102.

[0067] This obtaining step 302 can be carried out by the electronic control unit 110, in particular by the microprocessor 212 of the second electronic card 210 which can be integrated into the panel or remote from the panel depending on the embodiment considered.

[0068] In other embodiments, the direct model may be determined by a gold external diner to the panel, in which case the electronic control unit 110 is configured to obtain the direct model M from this computer.

[0069] A method 400 for developing the direct model M will now be described with reference to [Fig.4].

[0070] For example, this method 400 is implemented during the step 302 of obtaining the direct model M of the method 300 to determine the temperature map.

[0071] During a thermo-physical characterization step 402, the thermal protection panel 102 is characterized by its thermo-physical properties, its dimensions and the position of the temperature sensors 104 on the panel 102.

[0072] For this, the thermo-physical properties of the materials constituting the thermal protection panel 102, i.e. the metal used for the metal walls 102a, 102b (e.g. stainless steel) and the insulating material 102c (e.g. silica felt of type KF, KF-600-4 from Valmiera) are obtained by defining the thermo-physical parameters of the panel, such as the density p, the specific heat Cp and the thermal conductivity X. These parameters are obtained by measurements and / or calculations based on the values ​​provided by manufacturers of the materials used.

[0073] In the present example, the metal used for the two metal plates of the thermal protection panel is stainless steel (i.e. stainless steel) with a thickness of approximately 67 μm and the insulating material placed between these two plates is a layer of mineral wool with a thickness approximately equal to 20 mm. The thermophysical properties of the materials constituting the panel are given as an illustrative example in the table below: Thermo-physical property Materials Designation Unit Stainless steel Mineral wool Density (P) kg / m3 8010 48 Specific heat (CP) J / (kg.K) 490 840 Thermal conductivity (X) W / (mK) 14.7 0.03 - 0.045

[0074] [Table 1]

[0075] During an equation setting step 404, a thermal conduction equation is defined by the microprocessor 212 to model the propagation of heat in the panel 102.

[0076] For example, this equation is defined, from the thermo-physical parameters of the panel 102 previously determined during the thermo characterization step physics 402 as follows, this equation having the particularity of not including any term of heat source internal to the panel 102:

[0077] [Math 1]: MO -DV2T(t) - 0 dt ' '

[0078] This equation assumes on the one hand that the parameters p, Cp do not depend on time or temperature, since the temperature changes with time) and on the other hand that X does not depend on the position x, y, z or on the temperature since the temperature depends on the position.

[0079] where T(t) denotes the temperature as a function of time t, D=X / (p.Cp) denotes the thermal diffusion coefficient, V2 denotes the Laplacian operator, p denotes the density (in kg / m3), Cp denotes the specific heat at constant pressure (in J.kg '.K1), X denotes the thermal conductivity (in Wm *.K '). Equation Math 1 is associated with boundary conditions that are imposed on the faces of the panel 102 so as to fix the temperature at the ends of the panel 102.

[0080] During a meshing step 406, the thermal protection panel 102 is discretized according to a mesh 500 formed of a plurality of meshes 502. Advantageously, the thermal protection panel comprises nodes called “mesh nodes”, each node being formed by the interface between at least three meshes 502. In the context of the invention, the mesh 500 is obtained according to a finite element method (FEM: “Finite Element Method” in English).

[0081] An example of mesh 500 obtained at the end of meshing step 406 by a finite element method applied to panel 102 is illustrated in [Fig.5].

[0082] The thermal protection panel 102 (i.e. the two metal walls 102a, 102b and the insulating material 102c) is decomposed into volume by a set of preferably tetrahedral meshes connected two by two so as to discretize the panel in its volume. In other words, the mesh 406 of the panel consists of determining a plurality of points constituting the nodes of the mesh 500, each node being connected to three adjacent nodes so as to form a mesh 502, preferably tetrahedral, so that all of the meshes 502 cover the entire volume of the panel.

[0083] [Fig. 5] illustrates an example of a 500 mesh of a thermal protection panel having a length equal to 400 m, a width equal to 400 m and a thickness equal to 20 mm, where each of the two metal plates has a thickness equal to 74 μm. The thermo-physical properties of the materials constituting the panel are those described in Table 1 above. Under these conditions, the 500 mesh obtained for the whole panel comprises 60,000 tetrahedral 502 meshes as shown in the overview according to [Fig.5] (top figure).

[0084] [Fig.5] (bottom figure) is a close-up view at one corner of the plate metal located on the upper face of the thermal protection panel. In this example, the size of the 502 tetrahedral meshes is not uniform but tends to reduce at the edge. In this regard, it is preferable to have 3 to 5 meshes in the thickness of the stainless steel sheet so that the temperature field can be correctly determined. In practice, the mesh is therefore finer at the edge than the mesh at the glass wool.

[0085] [Fig.5] illustrates in perspective an aircraft engine nacelle 500, in which is implemented the 100 system.

[0086] According to the embodiment variant illustrated in [Fig.5], the body of the nacelle 500 constitutes the metal wall 102b on which is fixed the insulating material 102c which is itself covered with the other metal wall 102a, so as to form the thermal protection panel 102.

[0087] As illustrated, the mesh 500 is a set of tetrahedral meshes 502 joined together, so as to discretize the entirety of the panel 102. The mesh 500 has an elementary mesh 502 in the shape of a tetrahedron, as described previously with reference to [Fig.5].

[0088] Returning to [Fig.4], during a step 408, a calibration thermal source Se is initially selected. This is defined by a heat distribution law describing how the heat is distributed around a reference point PO in a space, for example in two dimensions (X, Y).

[0089] Preferably, the distribution law is selected to be of Lorentzian type, as defined by the following equation:

[0090] [Math. 2]: \ y) =----------42------ "MM

[0091] where L(x,y) is a two-dimensional Lorentz function designating the heat intensity at the point with coordinates (x,y), with the following parameters: the width at half-height T, the position on the abscissa and ordinate on which the distribution is centered (xO, yO), the maximum amplitude A0 at the position (xO, yO) as illustrated in [Fig.4].

[0092] In this example, these parameters are sufficient to fully characterize the thermal source. However, other distribution laws (or functions) may be selected, such as a Gaussian function defined by the same parameters as those indicated above. Depending on the selected function, other parameters may be considered to fully define the thermal source. The measured temperatures may be advantageously taken into consideration to determine the thermal source(s) with greater precision.

[0093] During a propagation step 410, a thermal excitation defined by the calibration thermal source Se is propagated in two dimensions on the surface of the panel 102 by solving the equation Math 1 with the boundary conditions applied to the mesh 500 representative of the panel (i.e. discretized panel), so as to obtain simulated temperatures Tse.

[0094] More generally, the simulated temperatures Tse are obtained by applying the calibration thermal source Se to the direct calibration model M. As previously, the direct model M is defined by the choice of the heat propagation equation according to certain hypotheses (step 404), the choice of physical parameters such as the dimensions of the panel 102 (step 404), the choice of a finite element mesh for the thermal protection panel (step 406), the choice of the boundary conditions for equation 1 described above.

[0095] Preferably, the model used in the method 300 which is the subject of the invention is validated before its first use.

[0096] By way of example and advantageously, the direct model may be validated experimentally, from temperature measurements obtained by the network of temperature sensors 104. In this regard, the position of each temperature sensor 104 is defined within the mesh 500. Indeed, as introduced previously, the position of the temperature sensors 104 relative to each other is predetermined but also the positioning of said sensors within the thermal protection panel 102 and the mesh 500 representative of said thermal protection panel 102. The experimental validation is obtained by the following steps.

[0097] During a heating step 412, the panel 102 is heated by physically applying a heat source Ee corresponding to the calibration thermal source Se, as defined during step 408.

[0098] During a measurement step 414, temperature data Tme are obtained by the first electronic card 200, from the voltages generated by the temperature sensors 104.

[0099] During a comparison step 416, the measured temperature data Tme are compared with the corresponding values ​​of the simulated temperatures Tse obtained Tse at the end of the propagation step 410.

[0100] For example, to carry out this comparison, the second electronic card 210 checks whether the temperature difference between each simulated temperature Tse and the measured temperature Tme of the temperature sensor closest to the mesh considered is less than or equal to a predetermined threshold Ase (i.e. A < Ase). In other embodiments (not illustrated), the analysis of the differences between the measured temperatures and the simulated temperatures may be carried out by a member located outside the thermal protection panel 102.

[0101] If not (i.e. A > Ase), the direct model is adjusted, by adjusting certain parameters of the direct model M during step 408. The direct model M is then modified.

[0102] Step 410 is repeated with the same calibration thermal source Se and the modified direct model so as to adjust the temperature field.

[0103] Steps 416, 404 and 410 are repeated until the temperature difference A is less than or equal to Ase for each of the meshes. At the end of this verification, the direct model M is experimentally validated.

[0104] In the present example, the reiteration is stopped if the stopping condition A< Ase is verified for each of the meshes. However, in alternative embodiments, only a subset of these meshes will be taken into consideration so as to accelerate the validation of the direct model.

[0105] In all cases, whether the validation relates to all or part of the measured temperatures, at the end of step 418, the direct model M is determined and validated experimentally from the temperatures measured by application of the thermal calibration source Se.

[0106] Once the direct model M is defined, it is a matter of solving the “inverse model” which consists of reconstructing the set of input parameters, i.e. the characteristics of the thermal source from a real temperature field as will be described in the remainder of the method 300.

[0107] Returning to [Fig.3], at the end of step 302, the direct model M is obtained.

[0108] During a propagation step 304, the microprocessor 212 applies a source thermal S of reference to the direct model M previously established at the end of the process 400. The propagation step 304 implemented corresponds to the propagation step 410 of the process 400 as described previously with reference to [Fig.4] (i.e. same mesh, same thermal conduction equation and same boundary conditions).

[0109] Thus, the microprocessor 212 simulates a propagation of heat coming from the reference thermal source S within the panel 102 using the direct model M, so as to obtain a field of simulated temperatures among which temperatures Ts simulated at the different locations of the temperature sensors.

[0110] The reference thermal source S can be defined by at least one thermal source function representative of a temperature distribution around a reference point PO corresponding to a position xO, yO of the reference thermal source S on the thermal protection panell02. Each function can be defined by at least one of the following parameters: a maximum amplitude A0 at the reference point PO, a width at half-height T.

[0111] In particular, the reference thermal source S can be defined by a combination, preferably linear, of at least two source functions Fl, F2 thermal, and more generally of a plurality of functions Fl, ..., FN, for example according to the following equation:

[0112] [Math. 3] = where N denotes a natural number such that N>1 and a; is a multiplying factor associated with the function F; which can be selected from a group of reference functions including a Lorentzian function, a Gaussian function.

[0113] By combining several source functions which may be of different types, it is possible to correspond as closely as possible to the real situation. For example, in the real case where a pipe breaks, this causes a leak of high-temperature fluid which can be finely restored at the level of the reference thermal source which is the combination of two thermal functions, i.e. one for the engine and the other for the damaged pipe.

[0114] For simplicity, we consider that the reference thermal source S is defined by a Lorentzian function, as previously described with reference to [Fig.4] for the calibration thermal source Se.

[0115] During a measurement step 306, the first electronic card 200 acquires the temperatures Tm from the voltages supplied by the temperature sensor network 104. The measured temperatures Tm are transmitted to the second electronic card 210. For example, the first electronic card 200 is configured to acquire and transmit the measured temperatures Tm at a predetermined time interval, for example of the order of 100 ms.

[0116] During a correlation step 308, the microprocessor 212 performs a correlation of the measured temperatures Tm with the estimated temperatures Ts. For this, the microprocessor 212 correlates a temperature value Tm measured in step a) with a simulated temperature value Ts obtained at the end of step b). Thus, a correlation is performed between the temperatures measured by the temperature sensors 104 and the simulated temperatures obtained by applying the direct model M as previously defined. This is done for each sensor.

[0117] For example, the correlation criterion used during the correlation step 308 is the absolute value of the temperature difference A=ITm-Tsl between the estimated temperature Ts and the measured temperature Tm, this difference being compared to a predetermined threshold As.

[0118] The predetermined threshold As can be defined as a function of the precision desired for obtaining the temperature map and / or the resources of the electronic cards, in particular of the second electronic card 212 whose calculation capacities of the microprocessor 212 are decisive.

[0119] According to a first approach, the mesh 500 is formed by a plurality of Ml meshes, where Ml is a natural integer such that Ml > N, N being the total number of temperature sensors 104 as seen previously. For each mesh, it is then necessary to identify the temperature sensor 104 which is closest to said mesh. The position of the temperature sensors 104 within the thermal protection panel 102 being predetermined, this identification is possible.

[0120] According to a second approach, for each mesh, a sphere centered around the mesh is defined, the sphere having a predefined volume, then the temperature sensor(s) 104 included in this sphere are identified. Therefore, for each mesh, it is possible to calculate the average value of the temperatures measured Tm by the temperature sensors 104 included in the sphere, for example by an arithmetic mean, and to correlate them with a simulated temperature Ts of the mesh considered. If there is only one temperature sensor 104, it is therefore the temperature Tm measured by this sensor which is correlated with that simulated in this mesh.

[0121] If the temperature difference A is greater than the predetermined threshold As, the microprocessor 212 adjusts the thermal source S, during an adjustment step 310. For example, to carry out this adjustment, the microprocessor 212 modifies at least one of the parameters defining the thermal source S, such as the type of function (e.g. Lo-rentzian, Gaussian), the maximum amplitude A0 or the width at half-maximum T.

[0122] Once the thermal source S has been adjusted, the microprocessor 212 applies the adjusted source S to the direct model M, during the propagation step 304 so as to obtain new simulated temperatures Ts.

[0123] Steps 308, 310, 304 are repeated as long as the temperature difference A between the measured temperatures Tm and the simulated temperatures Ts has not reached the predetermined threshold As, i.e. as long as A>As. Thus, the condition A=Tm-Ts < As constitutes a stopping condition for the adjustment of the reference thermal source.

[0124] Thus, at the end of the correlation step 308, if the stopping condition A=Tm-Ts < As is met, the microprocessor 212 validates the thermal source S and the simulated temperatures Ts obtained at the end of the propagation step 304 (or last iteration of step 304).

[0125] During a storage step 312, the simulated temperatures Ts thus obtained are stored in the form of a temperature map of the thermal protection panel 102, in a memory, for example the memory 218 of the second electronic card 210.

[0126] The mesh density forming the mesh 500 is selected to be sufficiently high so that all of the simulated temperatures Ts at the output of the propagation step 304 form a temperature map of the thermal protection panel 102 of sufficient resolution for the intended application.

[0127] Thus, thanks to the method according to the invention, a data item (even calculated) of tem temperature is available at each 502 mesh whereas standard methods use formulas (interpolation for example) to obtain a temperature value between two temperature sensors without taking into account the thermo-physical model of the panel.

[0128] It follows that the method of obtaining the temperature map according to the invention is simplified and consequently more efficient while providing high reliability.

[0129] At this stage, it should be emphasized that since the temperatures are known on the metal wall 102b, it is possible to know the temperature of an element located after the thermal protection panel, for example of an element in contact with this metal wall 102b or separated from the metal wall 102b by a distance of a few millimeters to about twenty centimeters. It is simply important that the temperature on the outside of the thermal protection panel is the same or minimal compared to that on the surface of the composite part if they are physically close. This could be interesting, for example, to monitor the temperature of more fragile composite parts located near the thermal protection panel.“Near the panel” means that the distance between the part(s) and the thermal protection panel is sufficient so that the temperature of the part(s) can be measured by the temperature sensors.

[0130] According to alternative embodiments, other stopping conditions may be defined using other comparison criteria, such as the temperature ratio Tm / Ts relative to a predetermined threshold.

[0131] In the example described, the control unit 110 and more particularly the first electronic card 200 and / or the second electronic card 210 is a computer system comprising a data processing unit, such as a microcontroller for the first electronic card 200 or a microprocessor for the second electronic card 210 and a main memory, such as a RAM memory, or “Random Access Memory”) accessible by the processing unit.The computer system further comprises, for example, a network interface and / or a computer-readable medium, such as, for example, a local medium (such as a local hard disk) or a remote medium (such as a remote hard disk accessible via the network interface through a communication network) or a removable medium (such as a USB key, from the English "Universal Serial Bus", or a CD, from the English "Compact Disc" or a DVD, from the English "Digital Versatile Disc") readable by means of a suitable reader of the computer system (such as a USB port or a CD and / or DVD disk reader). A computer program containing instructions for the processing unit is recorded on the medium and / or can be downloaded via the network interface. This computer program is, for example, intended to be loaded into the main memory, so that the processing unit executes its instructions.

[0132] Alternatively, all or part of these modules could be implemented in the form of hardware modules, that is to say in the form of an electronic circuit, for example micro-wired, not involving a computer program.

[0133] It will also be noted that the invention is not limited to the embodiments described above. It will indeed appear to those skilled in the art that various modifications can be made to the embodiments described above, in light of the teaching which has just been disclosed to them.

[0134] In the detailed presentation of the invention which is made above, the terms used must not be interpreted as limiting the invention to the embodiments set out in the present description, but must be interpreted to include all equivalents whose prediction is within the reach of those skilled in the art by applying their general knowledge to the implementation of the teaching which has just been disclosed to them.

[0135] Those skilled in the art will easily understand that the system and method for determining a temperature field as described above apply to all use cases where temperature constraints force the use of thermal protections to protect sensitive systems.

[0136] Preferably, the invention applies to commercial aircraft engine nacelles to detect abnormal temperature conditions on the external composite structure of the nacelle. Optionally, the invention makes it possible to collect information on the operation of the aircraft engine (turbojet).

[0137] Furthermore, the invention also makes it possible to better control the state of the thermal protection within the framework of a predictive maintenance approach, for example by recording the thermomechanical forces undergone by the engine nacelle over time using the temperature maps obtained from a limited number of measurements.

[0138] Although the invention has been described in the aeronautical context, in particular of an aircraft engine nacelle, it can also be applied to any other element requiring thermal protection with thermal monitoring, such as tanks, pipes or batteries and in fields other than that of aeronautics, such as automobiles or energy.

Claims

Claims

1. Method for determining (300) a temperature field of a part (102) comprising at least one surface subjected to a thermal source, said method comprising the following steps: a. measuring (306) temperatures (Tm) on said part (102) by means of a network of N temperature sensors (104), where N is a natural integer strictly greater than unity, said temperature sensors (104) being fixed on or in the part, according to a predetermined positioning, at a non-zero distance from the surface of the part; b. from a reference thermal source (S), determining (304) a set of simulated temperatures (Ts) within said part (102) by applying a direct model (M) of thermal conduction with a mesh (500) of the part (102) according to a finite element technique, said mesh (500) comprising a plurality of meshes (502); c. define the position of each temperature sensor within the mesh; d. for each of the meshes (502), correlate (308) the temperature values ​​(Tm) measured in step a) with a simulated temperature value (Ts) obtained at the end of step b); e. as long as a predefined stopping condition is not met at the end of step c), modifying (310) the reference thermal source (S) then repeating steps d) and e) with the reference thermal source (S) thus modified; f. once the stopping condition is met, storing (312) the set of simulated temperatures (Ts) determined during the last implementation of step b) as a temperature field of the room (102).

2. Method according to claim 1, in which the reference thermal source (S) is defined by at least one thermal source function representative of a temperature distribution around a reference point (PO) corresponding to a position (xO, yO) of the reference thermal source (S) on the part (102), said function being defined by at least one of the following parameters: an amplitude maximum (AO) at the reference point (PO), a width at half height (F).

3. The method of claim 2, wherein step d) comprises adjusting (310) at least one of the following parameters of said at least one thermal source function: position, amplitude, height at mid-height, type(s) of function.

4. Method according to claim 2 or 3, wherein said at least one function of the reference thermal source (S) is of Lorentzian or Gaussian type.

5. Method according to any one of claims 2 to 4, in which the reference thermal source (S) is defined by a combination, preferably linear, of at least two thermal source functions (F1, F2).

6. Method according to any one of claims 3 to 5, in which the reference thermal source (S) is defined by a combination of at least two thermal source functions of different type.

7. Method according to any one of claims 1 to 6, comprising a prior step of obtaining (302) said direct model (M) from at least one heat propagation equation defined as a function of the following physico-thermal parameters of the part (102): thermal conductivity (X), specific heat (Cp), density (p)-

8. Method according to claim 7, in which the direct model (M) is validated as a function of measured temperatures (Tme) on said part (102) in response to a thermal excitation (Ee) corresponding to a calibration thermal source (Se) used to establish the direct model (M).

9. Computer program (P) downloadable from a communication network and / or recorded on a computer-readable medium (218), characterized in that it comprises instructions for executing the steps of a method for determining a temperature field according to any one of claims 1 to 8, when said program (P) is executed on a computer (212).

10. System (100) for determining a temperature field of a part (102) comprising at least one surface subjected to a thermal source, said device comprising: a. an array of temperature sensors (104) for measuring temperatures on said part (102), said temperature sensors (104) being intended to be fixed on or in the part, according to a predetermined positioning, at a non-zero distance from the surface of the part; and b. calculation means (110; 202, 212) connected to the network of temperature sensors (104), the calculation means being configured to implement steps b) to e) of the method for determining the temperature field according to any one of claims 1 to 8.

11.

12. The system of claim 10, further comprising the part (102). The system of claim 11, comprising at least one part, for example at least one aircraft part, located side by side with the part (102).

13. Use of a system according to claim 12 for determining thermal stress on said aircraft part.

14. An aircraft engine nacelle (500) comprising a system (100) according to claim 10 to 12.

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