METHOD FOR PREDICTING TONAL AERODYNAMIC NOISE PRODUCED BY A COMPONENT FOR A MOTOR VEHICLE

Abstract

METHOD FOR PREDICTING TONAL AERODYNAMIC NOISE PRODUCED BY A COMPONENT FOR A MOTOR VEHICLE The present invention relates to a method for predicting aerodynamic noise produced by a component (4) for a motor vehicle (2), remarkable in that said method comprises the following steps: - carrying out a numerical simulation of fluid dynamics in steady state from a numerical model of the component; and - establishing a wall pressure distribution on a surface (6) of said component intended to be in contact with an airflow during the movement of the motor vehicle; and - evaluating the wall pressure distribution for the detection of an inflection point in said distribution, the prediction of the noise being based on said detection, where the presence of the inflection point indicates a risk of noise emanating from the component, while the absence of said inflection point indicates the absence of noise.(Figure to be published with the abbreviation: Figure 2).

Description

Title of the invention: METHOD FOR PREDICTING TONAL AERODYNAMIC NOISE PRODUCED BY A COMPONENT FOR A MOTOR VEHICLE technical field

[0001] The present invention relates to the field of motor vehicles, more particularly to the field of numerical simulations of aerodynamic elements for motor vehicles. Previous technique

[0002] Car manufacturers are increasingly striving to reduce aerodynamic noise during driving in order to improve the driving experience, particularly with the rise of the electrification of motor vehicles where the silence of electric motors makes the passenger compartment more receptive to various aerodynamic noises.

[0003] For example, rearview mirrors are one of the elements responsible for these noises in the passenger compartment, which can cause a whistling sound while driving. Manufacturers therefore seek to make rearview mirrors as aerodynamic and quiet as possible.

[0004] Conventionally, this whistling sound is detected by means of a dedicated wind tunnel test campaign, where a prototype rearview mirror is positioned at the center of the wind tunnel duct. Acoustic measurements are then taken using three microphones placed around the rearview mirror, outside the airflow, to detect fluctuations in acoustic pressure. A Fourier transform of these measurements, used as post-processing, reveals the whistling phenomenon of the rearview mirror.

[0005] However, this method involves high costs related to the manufacture of prototypes and the expensive use of wind tunnels, thus delaying the vehicle development process.

[0006] Published patent document CN 106777837 A discloses a method for predicting the intensity of urban road noise from a real data collection of flow, speed and lane of vehicles on a target urban road, and then substituting them into a pre-established road model to predict the noise intensity, so as to estimate the noise impact of road traffic before the construction of the new road.

[0007] However, the road noise prediction solution proposed by the document cannot be applied to predict possible noise that may be produced by an aerodynamic component of a motor vehicle, such as a rearview mirror. Description of the invention

[0008] The present invention aims to overcome at least one of the drawbacks of the aforementioned prior art. More particularly, the invention aims to provide a simple, efficient, and economical solution for effectively predicting the occurrence of aerodynamic noise from a component of a motor vehicle, such as a rearview mirror whistling sound.

[0009] To this end, the invention relates to a method for predicting a tonal aerodynamic noise produced by a component for a motor vehicle, remarkable in that said method comprises the following steps: - Performing a numerical simulation of fluid dynamics in steady state based on a numerical model of the element; and - establishing a wall pressure distribution on a surface of said element intended to be in contact with an airflow during the movement of the motor vehicle; and - evaluation of the wall pressure distribution for the detection of an inflection point in said distribution, the prediction of noise being based on said detection, where the presence of the inflection point indicates a risk of noise emanating from the element, while the absence of said inflection point indicates the absence of noise.

[0010] According to one embodiment, the wall pressure distribution comprises an evolution of a pressure coefficient as a function of a predefined distance extending along the surface of the element parallel to a direction of the simulated steady flow, said wall pressure distribution exhibiting a convex and / or concave tendency along the predefined distance.

[0011] According to one embodiment, the inflection point is detected when the wall pressure distribution shows a change in trend over the predefined distance, going from a convex trend to a concave trend, or vice versa.

[0012] According to one embodiment, the element is a rearview mirror for a motor vehicle, and the surface of said element comprises a peripheral band presented between a trailing edge of the rearview mirror and a peripheral line disposed on an external face of said rearview mirror at a distance from said trailing edge, said peripheral band extending circumferentially over an entire periphery of said rearview mirror.

[0013] According to one embodiment, the predefined distance extending parallel to the direction of the simulated steady flow is substantially perpendicular to the peripheral line and the trailing edge of the rearview mirror.

[0014] According to one embodiment, the predefined distance is equal to at least 5 mm and at most 200 mm.

[0015] According to one embodiment, the establishment of the wall pressure distribution along the predefined distance further includes a peripheral sweep over the entire periphery of the rearview mirror at the level of the peripheral band on the external face of said rearview mirror.

[0016] The invention also relates to a method for modeling a component for a motor vehicle, comprising: - a numerical modeling step of a digital model of said element, remarkable in that said modeling method further includes the steps of the method for predicting aerodynamic noise according to the invention, and in that when the inflection point is detected, the modeling method further includes a step of modifying the digital model locally at the right of a portion of the surface of the element where said inflection point is detected.

[0017] The invention also relates to a rearview mirror for a motor vehicle, remarkable in that said rearview mirror is modeled according to the method of modeling an element for a motor vehicle according to the invention, in which said element corresponds to said rearview mirror.

[0018] The invention also relates to a motor vehicle remarkable in that it includes at least one rearview mirror according to the invention.

[0019] The measures of the invention are advantageous in that the aerodynamic noise prediction method offers early and accurate detection of noise risks associated with the geometry of the element, from the earliest stages of development during its numerical modeling. This approach eliminates the need to build prototypes and conduct experimental tests, thereby accelerating the development process by reducing the number of simulations and wind tunnel tests, and thus making the development of the motor vehicle considerably less expensive. Brief description of the drawings

[0020] [Fig. 1] schematically represents the steps of a method for predicting aerodynamic noise produced by an element for a motor vehicle according to the invention, as well as the steps of a method for modeling said element;

[0021] [Fig.2] illustrates a perspective view of a rearview mirror of a motor vehicle according to the invention;

[0022] [Fig. 3] represents a graph showing the evolution of a pressure coefficient as a function of a predefined distance extending parallel to a direction of the simulated steady flow along an external face of the rearview mirror of [Fig. 2]. Detailed description

[0023] Fig. 1 schematically represents the steps of a method 103 for predicting a tonal aerodynamic noise, corresponding to a whistling sound, produced by an element for a motor vehicle according to the invention, as well as the steps of a method 100 for modeling said element.

[0024] The modeling process 100 includes a step 102 of numerically modeling a digital model of the element. The latter may correspond to a rearview mirror, a rear spoiler, or any other bodywork element likely to generate a whistling sound while the motor vehicle is in motion. More preferably, the element corresponds to a rearview mirror, such as the one illustrated in [Fig. 2].

[0025] Next, a step 104 of numerical simulation of stationary fluid dynamics is carried out from the numerical model of the element.

[0026] This simulation corresponds to a CFD simulation, from the English term "computational fluid dynamics," also designated by the acronym MFN, for "numerical fluid mechanics." It allows the study of the movements of a fluid relative to a surface of an element. Here, the simulated fluid corresponds to the flow of air against a surface of the element.

[0027] Preferably, step 104 involves an incompressible stationary CFD simulation solving the RANS (Reynolds-Averaged Navier-Stokes) equations, preferably using a k-epsilon or k-omega turbulence model, in which the density, velocity and pressure of the fluid do not vary with time during the simulation but only according to the position in the fluid.

[0028] Next, the whistling prediction method 103 includes a step 106 of establishing a wall pressure distribution on a surface of the element intended to be in contact with an airflow during the movement of the motor vehicle. Advantageously, the wall pressure distribution comprises an evolution of a pressure coefficient as a function of a predefined distance extending along the surface of the element parallel to a direction of the simulated steady flow. This evolution is represented in the graph in [Fig. 3]. Preferably, this surface corresponds to an external face 6 of the rearview mirror 4 of the motor vehicle 2 visible in [Fig. 2].

[0029] With reference to [Fig.2], the predefined distance d, along which the wall pressure distribution is established, is preferably between a peripheral line A disposed on the external face 6 and a trailing edge B of the rearview mirror 4, thus defining a peripheral band 8 extending circumferentially over a whole periphery of said rearview mirror 4.

[0030] Preferably, the peripheral line A corresponds to an aerodynamic narrowing of the rearview mirror 4, and therefore of its digital model, extending essentially parallel to the trailing edge B.

[0031] The predefined distance d is substantially perpendicular to the peripheral line A and the trailing edge B, or inclined at most 30° with respect to a perpendicular to at least one of these two. Preferably, the predefined distance is equal to at least 5 mm and at most 200 mm.

[0032] With reference to [Fig.3], we can see the evolution of the pressure coefficient Cp at the level of the ordinate axis, which represents the local pressure (at the right of the external face of the rearview mirror) with respect to atmospheric pressure, normalized by the dynamic pressure of the simulated steady flow.

[0033] Preferably, this refers to the wall pressure distribution carried out on the peripheral band of the rearview mirror and precisely along the predefined distance d represented at the level of the abscissa axis, and in which the positions of the peripheral line A and the trailing edge B are marked.

[0034] Two trajectories, T1 and T2, can be observed, corresponding to the evolution of pressure coefficients, respectively, for a rearview mirror surface that does not present a risk of whistling, and a rearview mirror surface that can cause whistling under driving conditions. The evolution of pressure coefficients can define a convex and / or concave trend.

[0035] With reference to Figures 1 and 3, the whistling prediction method 103 includes a step 108 for evaluating the wall pressure distribution to detect an inflection point I in said distribution. Advantageously, this is a simple post-processing of the incompressible stationary CFD simulation performed in step 104, allowing the determination of the risk of whistling related to the simulated geometry.

[0036] Advantageously, the prediction of the whistling is based on the detection of the inflection point I, where a presence of said inflection point I indicates a risk of whistling emanating from the rearview mirror (this is the case for the T2 trace), while an absence of said inflection point indicates the absence of whistling.

[0037] Preferably, the inflection point I is detected when the wall pressure distribution exhibits a change in trend corresponding to a change in concavity, shifting from a convex to a concave curve, or vice versa. At such a point I, the tangent crosses the curve (T2 plot) and the second derivative changes sign. The inflection point I is, by mathematical definition, either present or absent in a binary fashion.

[0038] The method 103 preferably comprises a peripheral scan around the entire periphery of the rearview mirror at the level of its peripheral band. This may correspond, for example, to a repetition of steps 106 and 108 for several distances d extending circumferentially around the entire periphery of the rearview mirror.

[0039] The T2 trace here indicates that the external face of the modeled rearview mirror 4 (of [Fig.2]) presents a risk of the appearance of whistling aerodynamic noise, particularly at about half the predefined distance d. In this regard, a correction of the geometry of the digital model of the rearview mirror 4 locally at the distance d would overcome the risk of the appearance of whistling.

[0040] Advantageously, the detection time of the inflection point I, and therefore of the risk of whistling, is almost immediate. Indeed, this is because said detection is carried out 100% digitally in post-processing of the calculation of the CFD simulation which already exists.

[0041] The modeling method 100 further includes a step 110 of modifying the digital model locally at the right of a portion of the surface of the element (e.g. the external face of the rearview mirror) where said inflection point I is detected, in order to attenuate the whistling that may emanate from the latter.

[0042] Thus, an element for a motor vehicle, such as the rearview mirror 4, modeled according to the method 100 according to the present invention, will not produce any tonal noise during the driving of the motor vehicle at the driving speeds defined in the numerical simulation in step 104.

Claims

Demands

1. A method (103) for predicting tonal aerodynamic noise produced by a component (4) for a motor vehicle (2), characterized in that said method (103) comprises the following steps: - performing (104) a numerical simulation of fluid dynamics in steady state from a numerical model of the component (4); and - establishing (106) a wall pressure distribution on a surface (6) of said component (4) intended to be in contact with an airflow during the movement of the motor vehicle (2); and - evaluating (108) the wall pressure distribution for the detection of an inflection point (I) in said distribution, the noise prediction being based on said detection, where the presence of the inflection point (I) indicates a risk of noise emanating from the component (4), while the absence of said inflection point (I) indicates the absence of noise.

2. Method (103) according to claim 1, wherein the wall pressure distribution comprises an evolution of a pressure coefficient as a function of a predefined distance (d) extending along the surface (6) of the element (4) parallel to a direction of the simulated steady flow, said wall pressure distribution exhibiting a convex and / or concave tendency along the predefined distance (d).

3. Method (103) according to claim 2, wherein the inflection point (I) is detected when the wall pressure distribution exhibits a change in trend over the predefined distance (d), changing from a convex trend to a concave trend, or vice versa.

4. A method (103) according to any one of claims 1 to 3, wherein the element (4) is a rearview mirror (4) of a motor vehicle (2), and the surface (6) of said element (4) comprises a peripheral band (8) presented between a trailing edge (B) of the rearview mirror (4) and a peripheral line (A) disposed on an external face (6) of said rearview mirror (4) at a distance from said trailing edge (B), said peripheral band (8) extending circumferentially over a whole periphery of said rearview mirror (4).

5. Method (103) according to claims 2 and 4, wherein the predefined distance (d) extending parallel to the direction of the simulated steady flow, is substantially perpendicular to the peripheral line (A) and the trailing edge (B) of the rearview mirror (4).

6. Method (103) according to claim 5, wherein the predefined distance (d) is equal to at least 5 mm and at most 200 mm.

7. Method (103) according to any one of claims 5 and 6, wherein the establishment of the wall pressure distribution along the predefined distance (d) further comprises a peripheral sweep over the entire periphery of the rearview mirror (4) at the periphery band (8) on the outer face (6) of said rearview mirror (4).

8. Method (100) of modeling an element (4) for a motor vehicle (2), comprising: - a step (102) of numerical modeling of a digital model of said element (4), characterized in that said method (100) of modeling further comprises the steps (104, 106, 108) of the method (103) of predicting aerodynamic noise according to any one of claims 1 to 7, and in that when the inflection point (I) is detected, the method (100) of modeling further comprises a step of modifying the digital model locally at the right of a portion of the surface (6) of the element (4) where said inflection point (I) is detected.

9. Rearview mirror (4) for motor vehicle (2), characterized in that said rearview mirror (4) is modeled according to the method (100) of modeling an element (4) for motor vehicle (2) according to claim 8, wherein said element (4) corresponds to said rearview mirror (4).

10. Motor vehicle (2) characterized in that it comprises at least one rearview mirror (4) according to claim 9.