EP3008457A1

EP3008457A1 - Method for determining a transition point and/or for determining wall shear stresses on surfaces around which surfaces a flow circulates, and measuring device

Info

Publication number: EP3008457A1
Application number: EP14757834.8A
Authority: EP
Inventors: Martin Stadlbauer; Jürgen Gründmayer; Felix VON PLEHWE
Original assignee: MTU Aero Engines AG
Current assignee: MTU Aero Engines AG
Priority date: 2013-06-14
Filing date: 2014-06-10
Publication date: 2016-04-20
Also published as: CN105492895A; US20160258827A1; WO2014198251A1

Abstract

The invention relates to a method for determining a transition point and/or for determining wall shear stresses on surfaces (1) around which surfaces a flow circulates by means of thermography, wherein the method comprises the following steps: providing a surface with a heat insulation layer (3) on the surface (1) around which a flow is to circulate, circulating a flow around the surface (1) around which a flow is to circulate, heating the surface (1) around which a flow circulates, contactless measuring of the emitted flow intensity of the surface (1) around which a flow circulates by means of a camera system (7), determining at least one temperature decay coefficient on the surface (1) around which a flow circulates and ascertaining the transition point and/or the wall shear stresses on the surface (1) around which a flow circulates. The invention further relates to a method for determining a transition point and/or for determining wall shear stresses on surfaces around which a flow circulates and/or the qualitative representation of the heat transfer into the flow.

Description

description

Method for determining a transition point and / or wall shear stresses on flow areas and measuring device

The present invention relates to a method for determining a transition point and / or wall shear stresses on flow areas according to claim 1. Furthermore, the present invention relates to a measuring device according to claim 12.

In order to understand flow processes on bodies that are flow around, it is important to determine the transition or transition point between laminar and turbulent flow by means of measurements. For this purpose, among other things, the so-called hot film manometry is applied, which, for example, along a line of a flow around the body

Transition point determined. With the help of hot film manometry measurements and a

appropriate calibration, the wall shear stress can be determined.

An object of the present invention is to propose a novel non-contact method for determining a transition point and / or wall shear stresses on flow areas. It is another object of the present invention to propose a corresponding measuring device.

The object of the invention is achieved by a method having the features of claim 1. It is further achieved by a measuring device having the features of claim 12.

According to the invention, a method is thus proposed for determining a transition point on surfaces which are flown over by means of thermography. The method can additionally or alternatively determine wall shear stresses on the surfaces which are flowed around.

A transition point generally describes the transition point from a laminar to a turbulent flow, or from a turbulent to a laminar flow, in particular along a surface, in space or along a line. The transition point is also called the instability point of the flow.

| Confirmation copy | Thermography describes an imaging method for measuring and / or displaying a temperature, in particular the surface temperature, of objects. In this case, the intensity of an infrared radiation emanating from a point or from a surface, for example, of the object, is taken as a measure of its temperature.

For the determination of the transition point and / or the wall shear stresses, the method according to the invention comprises the following steps: Providing a surface with a thermal barrier coating on the surface to be flowed or bypassed (short: flow around), or circulating (briefly: flowing around) the flow around Surface, heating the area around, non-contact measuring of heat emitted by the flow around the surface by means of a camera system, determining at least one

Temperaturabklingkoeffizienten on the flow around the surface and determining the transition point and / or the wall shear stresses on the surface flow around or qualitative visualization of the heat transfer into the flow.

The measuring device according to the invention is provided, set up and / or configured for determining the transition point and / or wall shear stresses on surfaces around which flows. Furthermore, the measuring device is configured to carry out at least the following method steps: heating the surface around which it flows, measuring heat emitted by the surface around it by means of a camera system, determining at least one temperature decay coefficient on the surface flowing around, and determining the transition point and / or wall shear stresses on the flow around it Area. For this purpose, it has the respective required devices.

In all the above and following embodiments, the use of the term "may be" or "may have" etc. is synonymous with "preferably" or "preferably", etc., and is intended to explain embodiments of the invention.

Advantageous developments of the present invention are the subject of subclaims and embodiments.

Embodiments of the invention may include one or more of the features mentioned below. As used herein, the term "thermal barrier coating" refers to a layer having low thermal conductivity properties. A measure of thermal conduction in a material or fabric is the thermal conductivity of the material or fabric.

A thermal barrier coating may be referred to as a poor thermal conduction layer. If, for example, a surface of a thermal insulation layer is heated by means of a heat source (eg by thermal radiation), then the heat is only passed on to a limited extent by this thermal insulation layer (or passed on to the surface only to a small extent).

Generally, there is no restriction on the thermal conductivity. However, it has been shown that it is advantageous if the thermal conductivity of the insulating layer is at least a factor of 5 smaller than the thermal conductivity of the base material.

As a thermal barrier coating, for example, Epoxidharzlack, e.g. ΙΟΟμηι be used.

In some embodiments of the invention, the thermal barrier coating has a thickness of a few micrometers (μηι), z. B. between 0.1 μηι and 500 μηι.

A thermal barrier coating may be referred to as a thermal barrier coating.

In some embodiments of the invention, the thermal barrier coating is applied to the surface of the surface to be flowed around and provided therewith. For example, the heat-insulating layer can be applied and fixed detachably or non-detachably on the surface, in particular by means of gluing. Alternatively, the thermal barrier coating can be painted, vapor-deposited, stapled, welded (eg by means of spot welding), soldered and clamped. Combinations of the said fastening variants are also possible according to the invention.

In certain embodiments according to the invention, the area to be flown around is provided with the heat-insulating layer on the surface already prefabricated. For example, can the thermal barrier coating under special manufacturing conditions (eg., Under vacuum) are manufactured with the surface to be flowed in another place.

In some embodiments of the invention, the surface to be flowed around actively. As used herein, the term "active" refers to a flow that is directed directly at the surface to be flowed, such as in a model in a wind tunnel where the flow is directed to the model To study certain flow phenomena, for example, the model can use an airplane

Wing profiles, a stator blade in a turbine or a car model to determine the air resistance.

In some embodiments of the invention, the surface to be flowed around is passively flowed around. As used herein, the term "passive" refers to a flow that inevitably flows around a profile because the profile itself is being moved, for example, in a blade (or impeller) in a gas turbine that undergoes a flow because the blade itself is moved (rotated).

In certain embodiments according to the invention, the area around which it flows is heated, in particular heated for a short time.

The heating of the flow around area is in some of the invention

Embodiments heated on the free surface of the thermal barrier coating, ie on the side of the thermal barrier coating, which is not directly connected to the flow area.

In certain embodiments according to the invention, the contactless measurement of emitted heat of the area around which it flows is effected by means of a camera system, in particular by means of an infrared camera system. An infrared camera is also called a thermal imaging camera or a thermographic camera.

In some embodiments of the invention, the heat emitted from the surface around which it flows is measured in a non-contact surface. In this case, a flat measurement is to be understood as meaning a measurement which does not gradually build up a planar measurement by means of a punctiform or linear measurement or scanning (as in the case of the so-called line scanning method), but which detects the surface to be measured with a single measurement. This surface measurement can be referred to as a full-surface measurement.

In some embodiments of the invention, the heat emitted from the surface around which it flows is measured without contact spatially and / or two-dimensionally on the surface. In certain embodiments of the invention, at least one

Temperature decay coefficient determined on the surface around which flows. In particular, the temperature decay coefficient can be determined at any location (synonymous with each point) on the surface and / or surface.

The temperature decay coefficient may be proportional to or may be assumed to be the heat transfer coefficient.

In some embodiments according to the invention, the transition point and / or the wall shear stresses are determined on the surface around which flows after the

Temperature decay coefficient was determined on the area flowed around. In other words, the transition point and / or the wall shear stresses on the flow-around surface are determined based on the determination of the temperature decay coefficient.

In certain embodiments of the invention, the surface of the

Thermal insulation layer on a surface applied to the functional layer. For example, the surface may have a layer with a high emissivity color (synonymous with: high emissivity color) as a functional layer. The term "emissivity" of a body, as used herein, indicates how much (heat) radiation the body emits in comparison to an ideal heat radiator, a so-called black body.

For example, polished iron has a low emissivity of about E = 0.1 (the emissivity E of a body may be given as the ratio of the radiance specific to a surface element of the body to the radiance radiated from a blackbody of the same temperature).

The emissivity should be in the relevant wavelength range and / or in the relevant

Thermal conductivity should be as high as possible, for example E 0.6.

By applying the functional layer can in some of the invention

Embodiments, the heat emitted from the surface around which flows are advantageously detected by means of the camera system with a higher signal-to-noise ratio compared with a surface around which no flow occurs without a functional surface.

In certain embodiments according to the invention, reference values of the heat given off from the surface around which the material flows are determined by means of the camera system, wherein the area to be flown around when detecting the reference values is not flowed around. Thus, at the Detection of the reference values, in particular the following steps: providing a surface with a thermal barrier coating on the surface to be flowed, heating the surface, contactless measurement of emitted radiation intensity in a λ-range (λ = wavelength) of the surface over time by means of a camera system, determining of at least one temperature decay coefficient at the surface.

In some embodiments of the invention, temperature decay constants are determined on the area being traversed, reference values being subtracted (or subtracted) from the measured values, or vice versa (i.e., the measured values are determined by the

Reference values deducted). The measured values relate here to the emitted radiation intensity of the surface around which flow is flowing around the surface to be flowed around. By means of this difference formation, measurement errors due to different local emission coefficients and thermal conductivities as well as inhomogeneous illumination on the surface can advantageously be avoided. It can thereby be achieved that only the heat transfer is imaged or effectively measured in the flow itself, heat transfer phenomena in the material of the circulating surface and / or in the thermal barrier coating play no or only a minor role.

In certain embodiments of the invention, the flow area is a surface of a turbine rotor blade. A turbine rotor blade may be a rotor blade of a

High-pressure turbine and / or a low-pressure turbine stage of a turbine. The

Turbine rotor blade may further be a rotor blade of a high pressure compressor and / or a low pressure compressor stage of a turbine.

In some embodiments of the invention, the area flowed around is a surface of a turbine stator blade. A turbine stator blade may be a stator blade of a

High-pressure turbine and / or a low-pressure turbine stage of a turbine. Furthermore, the turbine stator blade may be a stator blade of a high pressure compressor and / or a low pressure compressor stage of a turbine.

In certain embodiments of the invention, the camera system is a

Infrared camera system or has such. An infrared camera system can be used as

Thermal imaging camera system, thermographic camera system, thermal camera system or as

Thermal imaging device are called.

In some embodiments of the invention, the infrared camera is connected to a borescope or has a borescope. Other synonyms for Boroscopes are: borescopes, endoscopes, technoscopes, autoscopes or intrascopes. By means of a borescope (eg an infrared borescope) or other optics may be used in turbine applications

The decay behavior of the heat given off is measured on previously heated, circulating rotor surfaces over several revolutions of the rotor.

In some embodiments of the invention, the area around which it flows is heated by means of a flash lamp or by means of a laser. By means of a flashlamp or by means of a laser, the surface around which it flows can be heated (briefly) with or without flow around within a short period of time. By means of special fast infrared cameras (eg so-called Indium Antimonide (InSb) "Focal Plane Array" (FPA) cameras with a refresh rate of around 800 images per second and integration times of less than 1 με), the

Temperature decay behavior of the surface recorded over the entire surface and the decay constant for each location on or above the surface are determined.

In certain embodiments of the invention, heating (eg, by means of

Flash lamp or laser), the non-contact measurement of the heat given off and the

Determining the temperature decay coefficient at least a second time, for example, to optimize the signal-to-noise ratio by averaging the measurement results. Further measurements can further optimize the signal-to-noise ratio.

In certain embodiments of the invention, the wall shear stresses are determined by means of previously determined Temperaturabklingkoeffizienten. The correlation between the wall shear stresses and the temperature decay coefficients is based on the

Following explained context. The temperature decay coefficients are proportional to the heat transfer coefficients. Furthermore, for incompressible flows, the so-called Reynolds analogy applies, which states that the momentum and heat transfer are similar in the case of friction-affected flows. Consequently, based on a heat transfer measured, for example, by means of an infrared camera system, the pulse transmission can be determined. By means of the pulse transmissions, the wall shear stresses can be determined. Thus, a full-surface wall shear stress measurement or Quasiwandschubspannungsmessung can be performed contactless with the inventive method. Furthermore, a simple visualization (quantitative) of the heat transfer into the flow can be realized.

In certain embodiments of the present invention, the heat emitted from the flow around surface is measured on the flow side of the flow around surface.

In some embodiments of the invention is the Measuring device for determining a transition point and / or of

Wall shear stresses on the flowed surfaces to perform the following

Process steps configured: heating the surface around which flows, contactless measuring of heat emitted by the surface around it by means of a camera system, determining at least one temperature decay coefficient at the surface and determining the transition point and / or the wall shear stresses on the surface around which flows.

In certain embodiments according to the invention, the transition point and / or the wall shear stresses on the surface around which the material flows are determined by the measurement data of the non-contact measurement of the heat given off and / or the at least one

Temperature decay coefficients are analyzed. An analysis may include a comparison with, for example, other measurement data acquired earlier or with measurement data from tables or other comparison data (or reference data). An analysis may include a comparison with historical data from previous measurements. On the basis of this analysis, the transition point can be determined and / or the wall shear stresses on the surface around which it flows can be determined.

In some embodiments according to the invention, the transition point and / or the wall shear stresses on the surface around which the material flows are determined by the measurement data of the non-contact measurement of the heat released and / or the at least one

Temperaturabklingkoeffizienten be compared with a comparison device with other data.

In some embodiments of the invention, the measuring device is a test bench. The measuring device may include an evaluation unit of the measurement results.

Some or all embodiments according to the invention may have one, several or all of the advantages mentioned above and / or below.

An advantage of a heat-insulating layer on the surface to be flowed over may be that a suitably applied from the outside heating to a flat side of the

Thermal insulation layer does not continue on the other surface side, in particular not on the side that is directly connected to the flow around the surface, or at least continues only to a small extent. Thus, it can be advantageously prevented that the heat applied from the outside heats or at least does not substantially heat the flow area located below the heat-insulating layer. Consequently, no heat, or at most only a small part thereof, by means of heat conduction (synonymous with heat conduction) in the flow around part be forwarded, which would not be available for the measurement method according to the invention with the camera system.

Another advantage of the thermal barrier coating is the achievable, better spatial resolution in the non-contact measurement of the heat emitted from the surface around which it flows. This better spatial resolution therefore results that the heat remains localized, not smeared and not, or at least only to a lesser extent, forwarded by heat conduction on the surface and distributed over a large area.

By means of a heat-insulating layer on a surface to be flowed around, for example a blade, advantageously a high contrast can be achieved in the measurement of the heat given off.

The quantitative calculation of a heat transfer coefficient can by means of a

Thermal insulation layer be significantly less flawed.

The present invention is explained below by way of example with reference to the accompanying drawings. In the schematically simplified, single figure:

1 shows a side view of a flow around surface with thermal barrier coating,

which is heated by a flashlamp, and a camera system.

Fig. 1 shows a side view of a flow around surface 1 with a two-dimensionally connected thereto thermal barrier coating 3, which is heated by a flash lamp 5 for a short time. Furthermore, a camera system 7 is shown in simplified form, which detects the heat emitted by the thermal barrier coating 3 without contact.

By means of the thermal barrier coating 3, on the one hand, it can be at least largely prevented that a portion of the heat is passed on to the area 1 which flows around it. On the other hand, the heat on or along the surface of the thermal barrier coating 3 is not forwarded or distributed. Thus, due to the thermal barrier coating 3, a high contrast can be achieved in the non-contact measurement of the heat released. Furthermore, due to the

Thermal insulation layer 3 is the quantitative calculation of the heat transfer coefficients much less buggy.

The camera system 7 may, for example, an infrared camera system with a high

Refresh rate (for example, around 800 frames per second) and short integration times (less than 1 μβ). With such an infrared camera system, the

Temperature decay behavior of the surface of the thermal barrier coating 3, which is connected to the flow-around surface 1, recorded over the entire surface and the decay constant for each location on the surface are determined. Since the heat transfer coefficient at the transition from laminar to turbulent flow 9 changes, so that any existing transition region can be detected over the entire surface.

The process goes much further! The method is generally applicable to any type of flow around surface, such. For example, scale models of cars, trains and planes

Wind tunnels. For sporting goods developments, this procedure (such as bicycle,

Motorcycle helmets, golf balls, etc.) also applicable. In the development of wind power plants (especially in rotor development), this method could also be applied.

LIST OF REFERENCE NUMBERS

Reference number Description

1 area around

3 thermal barrier coating

5 flash lamp

7 camera system

9 flow; laminar / turbulent

Claims

claims

1. A method for determining a transition point and / or of

Wall shear stresses on flow-around surfaces (1) by means of thermography, the method comprising the steps:

- Providing a surface with a thermal barrier coating (3) on the

flowing around surface (1);

- Flow around the surface to be flowed around (1);

- Heating the flow around the surface (1);

- Non-contact measurement of emitted radiation intensity of the flow around the surface by means of a camera system (7);

Determining at least one temperature decay coefficient at the

flow around surface (1); and

Determining the transition point and / or the wall shear stresses on the

flow around area (1)

and / or surface representation of the decay coefficients.

2. The method of claim 1, wherein the surface has a on the thermal barrier coating (3) applied functional layer.

3. The method according to claim 1 or 2, further comprising the step:

- Determining reference values, wherein the emitted radiation intensity of the flow-around surface (1) by means of the camera system (7) without flow around the surface to be flown around (1) is measured.

4. The method of claim 3, further comprising the step of:

- Determining the Temperaturabklingkonstanten on the flow around surface (1), wherein the reference values are subtracted from the measured values of the heat emitted the flow around surface (1) with flow around the surface to be flowed, or vice versa.

5. The method according to any one of the preceding claims, wherein the flow around surface (1) is a surface of a turbine rotor blade.

6. The method according to any one of the preceding claims, wherein the flow around surface (1) is a surface of a Turbinenstatorschaufel.

7. The method according to any one of the preceding claims, wherein the camera system (7) is an infrared camera system or has such.

8. The method according to any one of the preceding claims, wherein the infrared camera is connected to a borescope or has such.

9. The method according to any one of the preceding claims, wherein the flow around surface (1) by means of a flash lamp (5) or by means of a laser is heated.

10. The method according to any one of the preceding claims, wherein the

Wall shear stresses are determined by means of the previously determined Temperaturabklingkoeffizienten.

11. The method according to any one of the preceding claims, wherein the heat emitted from the flow-around surface (1) on the flow side of the flow-around surface (1) is measured.

12. Measuring device for determining a transition point and / or of

Wall shear stresses on flows around surfaces (1), wherein the measuring device is configured to carry out the method steps: - Heating the flow around the surface (1);

- Non-contact measuring of heat emitted by the flow around the surface (1) by means of a camera system (7);

Determining at least one temperature decay coefficient at the

flow around surface (1); and

Determining the transition point and / or the wall shear stresses on the

flow around area (1)

and / or the qualitative representation of the heat transfer into the flow.