JP2006343179A - Measurement of reynolds number or the like utilizing boundary layer turbulent flow transition phenomenon - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new measuring method capable of determining easily a parameter in hydrodynamics including an effective Reynolds number of fluid in an optional dynamic pressure without being influenced by a rotational frequency change or the like of a blower in a wind tunnel experiment. <P>SOLUTION: In this Reynolds number measurement, a boundary layer transition point position is measured in the state where a specimen is installed in some wind tunnel and the air flow state such as a flow velocity is set, and the Reynolds number per unit length is allowed to correspond to the boundary layer transition point position, and correspondence results in each air flow state are summarized on a table and provided as a database, to thereby detect the Reynolds number per unit length from a measured value of the boundary layer transition point. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a technique for measuring a hydrodynamic parameter typified by an effective Reynolds number of a fluid at an arbitrary dynamic pressure by utilizing a boundary layer turbulent transition phenomenon of a fluid flowing around a certain object.

  The Reynolds number is an important physical quantity when performing aerodynamic analysis in low-speed wind tunnel tests used for developing high-performance aircraft technologies. This Reynolds number R is a dimensionless value. When a typical length of an object in a flow is L, velocity is U, density is ρ, viscosity is η, and kinematic viscosity is ν, R = ΡLU / η = LU / ν. That is, the physical meaning can be considered as the ratio of the magnitude of inertia to the magnitude of viscosity.

First, the measurement of the effective Reynolds number using a turbulent sphere in the wind tunnel test will be explained. As shown in the upper part of FIG. 5, the turbulent sphere is connected to a spherical body with a straight tube-shaped pressure guiding tube facing the center point, and a total pressure hole is opened on a spherical surface on the axial extension line of the pressure guiding tube. Is a structure in which a static pressure hole is opened at a position that forms an angle of 22.5 ° with the axis of the pressure guiding tube that is the opposite surface of the sphere, and a tube that communicates all the pressure holes and the static pressure hole is disposed in the pressure guiding tube. It is what you did. The force due to the fluid applied to the turbulent sphere is made dimensionless by the product of the maximum cross-sectional area and the dynamic pressure of the turbulent sphere, and the drag coefficient Cd becomes 0.3, or the pressure measured by the static pressure hole is the total pressure hole. The Reynolds number when the pressure coefficient Cp, which is a value divided by the measured pressure, becomes −1.22, is called the critical Reynolds number, and this value is 385,000 in the atmosphere in the case of a sphere. This critical Reynolds number has the physical meaning above which the flow in the boundary layer is no longer limited to laminar flow. In order to obtain the critical Reynolds number at the time of experiment, when the dynamic coefficient is changed and the drag coefficient or pressure coefficient is plotted on the vertical axis and the Reynolds number at that time is plotted on the horizontal axis, the graph is as shown in FIG. The critical Reynolds number during the experiment is estimated from this graph. Then, the value obtained by dividing the critical Reynolds number in the atmosphere by the critical Reynolds number at the time of the experiment is defined as the turbulence constant TF.
TF = Rc / Rtc ……………………………………………………………… (1)
The effective Reynolds number R is generally calculated by multiplying the experimental Reynolds number Rt by the turbulence constant TF to calculate the effective Reynolds number in the wind tunnel test. (See Non-Patent Document 1)
R = TF ・ Rt ………………………………………………………………………………………………………… (2)

  However, this effective Reynolds number measurement method uses a turbulent constant TF, which is a value obtained by dividing the critical Reynolds number in the atmosphere by the critical Reynolds number at the time of experiment, and obtains the effective Reynolds number by multiplying the experimental Reynolds number by this turbulent constant. Therefore, since it is assumed that the effective Reynolds number is a constant multiple of the experimental Reynolds number, the correct effective Reynolds number at an arbitrary dynamic pressure cannot be measured. In particular, there is a problem that it is not possible to take into account influences such as changes in flow velocity or changes in the degree of flow turbulence when the rotational speed of the blower is switched.

  On the other hand, in a wind tunnel experiment, a viscous fluid has a region called a boundary layer in which a shearing force that reduces a flow velocity acts between a fluid flow and an object with which the fluid contacts. The boundary layer includes a laminar boundary layer and a turbulent boundary layer, and changes from the former to the latter as it flows on the object surface. This changing position is called the boundary layer transition point, and this position is known to change depending on the hydrodynamic parameters such as the surface state of the object, the fluid Reynolds number, the degree of fluid turbulence, and heat transfer. .

  Incidentally, Non-Patent Document 1 states that the boundary layer on the surface of an object is transitioning to a turbulent flow in an aircraft, a ship, a high-speed railway vehicle, an automobile, a fluid machine, an internal flow path of a piping system, etc. Then, the frictional resistance of the fluid gives a non-negligible energy loss. If it is judged that if the boundary layer transition can be delayed and the flow can be kept in laminar flow for as long a distance as possible, the frictional resistance can be greatly reduced, and there is a precursor to the transition to turbulence and flow separation. Discloses a technique for artificially introducing a change in the direction of canceling transition or separation in a flow. Specifically, a large number of small fluid passages are provided side by side on the object surface member, and a cavity is provided inside the object behind the object. The cavity is connected to an air drive source, and dynamically making the air drive source positive or negative with respect to the external pressure creates a flow of blow or suction driven by the air drive source, On the surface, there is a flow of blowout or suction from the fluid passage. As a result, velocity fluctuations in the direction perpendicular to the wall surface are excited in the boundary layer on the surface of the object, and fluctuations in the direction that effectively cancels transitions and separations grow, and transitions and separations are suppressed.

In the non-patent document 2, the present inventors have also announced the measurement of the model installed in the wind tunnel experiment and the boundary layer transition point. Because the position and characteristics of boundary layer transitions are caused by changes in Reynolds number and other parameters, grasping boundary layer transition characteristics is a reliable real-world characteristic from phenomenon clarification and wind tunnel test results. Based on the idea that it will lead to prediction, a comparative method for measuring the boundary layer transition position using a Preston tube, a hot film, an infrared camera, and a temperature-sensitive liquid crystal film is presented.
Japanese Patent Laid-Open No. 10-28115 “Fluid Control Method” Released on October 20, 1998 Shojiro Shindo, “Low-Speed Wind Tunnel Experiment” August 20, 1992, Corona Publishing, p.36-40 Yuko Yokokawa, Yoshinao Aoki, Yoshiro Morita, et al. “A trial of measuring all-machine model transition in a 6.5m × 5.5m low-speed wind tunnel” JAXA-SP-04-002, published on January 28, 2005

  The subject of the present invention is a measurement method that solves the problems in the effective Reynolds number measurement method using the turbulent sphere described above, i.e., without being affected by changes in the rotational speed of the blower, etc. It is to present a novel measurement method that can easily obtain hydrodynamic parameters such as effective Reynolds number from wind tunnel experiments.

  The present invention presents a method for obtaining the value of a specific parameter such as the Reynolds number by measuring a phenomenon in which the position of the turbulent transition in the boundary layer changes under an environment where other parameters are not changed. The parameter that has the greatest influence on the boundary layer transition is the surface state of the object and the Reynolds number. When the surface state of the object is the same, its position is almost determined by the Reynolds number. Associate the Reynolds number with the position of the boundary layer transition point in the set state, measure this position, and use the result to determine the unit length based on the airflow state when the position of the boundary layer transition point is associated Measure the Reynolds number per hit.

The method for obtaining the Reynolds number of the present invention is to install an object in a certain surface state in a wind tunnel, and use a fluid such as air having constant physical properties such as density, viscosity and kinematic viscosity, and the degree of fluid turbulence and heat transfer. The velocity of the fluid is changed under the condition that is stable, and the relationship between the Reynolds number in each airflow state and the boundary layer turbulent transition position on the surface of the object is stored as table information in advance. The Reynolds number per unit length of the fluid in the wind tunnel is obtained from the boundary layer turbulent transition position data measured in the state based on the table information.
The table information includes 1) a table prepared in advance from data obtained by measuring the Reynolds number in a certain airflow state and the boundary layer turbulent transition position on the object surface, and 2) the same surface state and shape as the object used for measurement. A table created from the boundary layer turbulent transition position predicted from fluid dynamics theory, subject to the Reynolds number and state of the airflow, 3) the same surface state and shape as the object used for measurement, the Reynolds number of the airflow, Reynolds in a certain airflow state by combining the above three methods such as a table created from a boundary layer turbulent transition position predicted from computer simulation, or 4) experiment and theory, or experiment and computer simulation Number and the predicted boundary layer turbulent transition position on the object surface. To adopt a Bull.

  The hydrodynamic parameter calculation method of the present invention is based on the Reynolds number R obtained by the method according to claim 1, wherein the representative length of the object is L, the velocity is U, the density is ρ, and the viscosity is When η and kinematic viscosity are ν, an unknown number of any one of fluid density ρ, viscosity η, or kinematic viscosity ν is calculated based on the relationship represented by R = ρLU / η = LU / ν. .

  Furthermore, another hydrodynamic parameter calculation method according to the present invention is to install an object in a certain surface state in a wind tunnel, and use a fluid such as air whose physical properties such as density, viscosity and kinematic viscosity are constant, Boundary layer transition when changing one of the parameters of the surface of a specific shape, the degree of turbulence of the fluid, and the heat transfer parameters in a state where two of the parameters are stable and a given airflow is flowing Data obtained by measuring points is stored in advance as table information, and one unknown parameter is evaluated from boundary layer turbulent transition position data of the specific shape measured in the predetermined airflow state in an experiment.

The method for obtaining the Reynolds number of the present invention is to install an object in a certain surface state in a wind tunnel, and use a fluid such as air having constant physical properties such as density, viscosity and kinematic viscosity, and the degree of fluid turbulence and heat transfer. The fluid velocity is changed under a stable state, and the relationship between the Reynolds number in each airflow state and the data obtained by measuring the boundary layer turbulent transition position on the object surface is stored as table information in advance. The Reynolds number per unit length of fluid in the wind tunnel is obtained from the boundary layer turbulent transition position data measured in the air flow state in the experiment based on the table information. When the effective Reynolds number is intentionally increased by a turbulent grid, etc., the effective ray per unit length based on a certain air flow state is used. It can be easily measured as Luz number.
By measuring the boundary layer transition phenomenon, it is possible to easily measure the effective Reynolds number based on the state of the flow without measuring the density, viscosity and flow velocity of the fluid.

  Further, from the Reynolds number R thus obtained, when the representative length of the object is L, the velocity is U, the density is ρ, the viscosity is η, and the kinematic viscosity is ν, R = ρLU / η Based on the relationship represented by = LU / ν, it is possible to easily calculate any one of the fluid density ρ, viscosity η, or kinematic viscosity ν.

  In addition, the external factor evaluation method that affects the boundary layer turbulent transition phenomenon according to the present invention is a method in which an object having a certain surface state is installed in a wind tunnel and the physical properties such as density, viscosity, and kinematic viscosity are constant. This was used to change the surface condition of an object of a specific shape, the degree of fluid turbulence, and one other parameter in a state where a predetermined air flow was flown with two of the heat transfer parameters stabilized. By storing the measured data of the boundary layer transition point at the time as table information in advance, one parameter that is easily unknown from the boundary layer turbulent transition position data of the specific shape measured in the predetermined airflow state in the experiment Can be evaluated.

  A region called a boundary layer is formed between the flow of the viscous fluid and the object with which the fluid contacts. The boundary layer includes a laminar boundary layer and a turbulent boundary layer, and changes from the former to the latter as it flows on the object surface. This changing position is called a boundary layer transition point, and it has been elucidated that this position changes depending on various factors such as the surface state of the object, fluid Reynolds number, fluid turbulence, and heat transfer. The measurement using the boundary layer turbulent transition phenomenon of the present invention is intended to detect useful parameters in hydrodynamics represented by the Reynolds number by measuring the position of this transition point.

  Although it is not necessary to specify the measurement method of the boundary layer transition point in particular, here, as one form, a cylindrical member is placed in the flow field in the wind tunnel and the outer surface transitions from the laminar boundary layer to the turbulent boundary layer. The description will be made by detecting the position from the change of the heat transfer coefficient. That is, as shown in FIG. 1, the hollow cylindrical member 1 is provided with a heater 2 for uniformly heating the outer surface and a temperature sensor 3 arranged in an array in the flow direction. If the flow state of the boundary layer formed in the vicinity of the object surface is uniform, the heat radiation on the outer surface of the cylindrical member 1 should be uniform, but in reality, the boundary layer is disturbed from the laminar boundary layer. Since a phenomenon of transition to the flow boundary layer occurs, the heat dissipation state changes depending on the position. This change appears as a change in the surface temperature and can be detected by the temperature sensor 3 arranged in an array in the flow direction, and a boundary layer transition point can be detected as the change point. Incidentally, the shape of the hollow cylinder used by the present inventor was measured by passing a fluid through the inside of the cylinder using an outer diameter of 50 mm, an inner diameter of 49 mm, a length of 100 mm, a material having a metal and a smooth surface.

  First, regarding the measurement of effective Reynolds number, the position of the turbulent transition in this boundary layer is changed by changing only the flow velocity in an environment where the parameters other than the Reynolds number that affect the boundary layer transition point are not changed. The phenomenon that changes is measured and the data is accumulated. That is, in a certain wind tunnel facility, the hollow cylindrical body 1 is installed in the wind tunnel, and the boundary layer transition point is measured by changing the fluid velocity. In this case, the smooth metal surface is stable, the surface state of the object is regarded as stable, and heating by the heater 2 is also in a uniform stable state, so that heat transfer can also be regarded as stable. Further, since the fluid is air, its density and viscosity can be regarded as stable. The boundary layer transition point is measured by the temperature sensor 3 while changing the flow velocity under such conditions, and the correspondence between the flow velocity and boundary layer transition point data under the conditions is stored as table information. The boundary layer transition point data obtained here can be regarded as corresponding to the Reynolds number because it is understood that the change due to factors other than the Reynolds number is not superimposed in this case. If the Reynolds number corresponding to each flow velocity is calculated based on the Reynolds number defining formula R = ρLU / η = LU / ν, a correspondence table of boundary layer transition points corresponding to the Reynolds number is obtained. In order to obtain versatility, it is desirable to store data as the Reynolds number as the Reynolds number per unit length. This data can be used for Reynolds number measurement in a model experiment performed in the wind tunnel with the same object surface. That is, by measuring the boundary layer transition phenomenon, it is possible to easily measure the effective Reynolds number based on the flow state without measuring the density, viscosity, and flow velocity of the fluid.

The correspondence table of boundary layer transition points corresponding to the Reynolds number is as described above.
1) A table created in advance from data obtained by measuring the Reynolds number in a certain airflow state and the boundary layer turbulent transition position on the surface of the object,
Not only
2) A table created from the boundary layer turbulent transition position predicted from the theory of fluid dynamics, subject to the same surface state and shape as the object used for measurement, and the Reynolds number and state of the airflow.
3) A table created from the boundary layer turbulent transition position predicted from computer simulation, subject to the same surface state and shape as the object used for measurement, and Reynolds number and state of the airflow,
4) A table created from the Reynolds number in a certain airflow state and the predicted boundary layer turbulent transition position on the object surface by combining the above three methods such as experiment and theory, or experiment and computer simulation,
Can be used.
Also, the hydrodynamic parameter calculation method according to the present invention is based on the Reynolds number R obtained by this method, the representative length of the object is L, the velocity is U, the density is ρ, the viscosity is η, and the kinematic viscosity When the rate is ν, it is possible to calculate any one of the unknowns of fluid density ρ, viscosity η, and kinematic viscosity ν based on the relationship expressed by R = ρLU / η = LU / ν. Become.

  Next, the relationship between the Reynolds number and the boundary layer transition point proposed by the present invention in the small low turbulence wind tunnel established by the present inventors in the Research Division of the Japan Aerospace Exploration Agency, that is, the Reynolds number is changed. For example, the boundary layer transition point changes correspondingly, and the experimental results demonstrating that the Reynolds number can be measured by measuring this boundary layer transition point are shown. The specimen was NACA0015, the material was carbon FRP, the wind tunnel width direction dimension B was 1.0 m, and the longitudinal dimension C was 0.4 m, and it was installed in the wind tunnel with an angle of attack of 0 ° C. Unlike the actual aircraft wing, this two-dimensional wing shape has the same cross-sectional shape as shown in FIG. 2 and is the same for all positions in the B direction. As the boundary layer transition point position sensor, a Preston tube having an inner diameter of 0.3 mm and an outer diameter of 0.5 mm as shown in FIG. 3 is used, and the pressure detected by arranging the Preston tube in the blade surface flow direction. The boundary layer transition point position is detected from the change. The main flow velocity (corresponding to the flow velocity at the sensor installation position) is switched between 20 m / s, 30 m / s, 40 m / s, 50 m / s, and 58 m / s. The pressure was measured at 11 locations of Preston tube arrangement positions (X / C) 20, 30, 40, 45, 50, 55, 60, 65, 70, 75, 80. Here, C is the dimension in the front-rear direction of the previous two-dimensional wing shape, in this case 0.4 m, and the value of X / C is indicated by the front end position of the wing being 0 and the rear end position being 100. The measurement results are shown in Table 1. The pressure coefficient Cp, which is a dimensionless value obtained by dividing the total pressure measured by the Preston tube by the main flow pressure, is taken on the vertical axis, and the measurement position X / C is taken on the horizontal axis. A graph of this is shown in FIG. Since the inflection point rising rapidly in this graph corresponds to the boundary layer transition point, the measurement position X / C is taken in as the boundary layer transition point at each flow velocity. Specifically, a polygonal line is drawn on the curve parts “before rising”, “during rising”, and “after rising”, and the intersection is set as the Onset point and End point of the transition, and the intermediate point is estimated as the transition point.

ここで、圧力データはすべて主流静圧との差で示してある。また、空気の粘度は25℃の、密度は30℃の乾燥空気を仮定してその値を用いた。
それぞれの流速に対応した単位長さ（１ｍ）当たりのレイノルズ数を算出すればレイノルズ数は、レイノルズ数の定義式Ｒ＝ρＬＵ／η＝ＬＵ／νに基づき、算出すると
主流流速 単位長さ当たりのレイノルズ数
20ｍ/s 1301×10^３/ｍ
30ｍ/s 1752×10^３/ｍ
40ｍ/s 2602×10^３/ｍ
50ｍ/s 3253×10^３/ｍ
58ｍ/s 3773×10^３/ｍ
となる。図４のグラフは境界層遷移点位置を示す立ち上がり位置が、上記のようなレイノルズ数値とみなされる主流流速に対応して大きく異なることを示しており、この境界層遷移点位置が感度のよいレイノルズ数検知パラメータであることを実証している。なお、ここで得られた境界層遷移点データはこの場合レイノルズ数以外の要因による変化分は重畳されていないと解されるので、レイノルズ数に対応したものとみなすことができる。

Here, all the pressure data are shown as differences from the mainstream static pressure. Further, assuming that the viscosity of air is 25 ° C. and the density is 30 ° C., the values are used.
If the Reynolds number per unit length (1 m) corresponding to each flow velocity is calculated, the Reynolds number is calculated based on the Reynolds number definition formula R = ρLU / η = LU / ν. Reynolds number
20m / s 1301 × 10 ³ / m
30m / s 1752 × 10 ³ / m
40m / s 2602 × 10 ³ / m
50m / s 3253 × 10 ³ / m
58m / s 3773 × 10 ³ / m
It becomes. The graph of FIG. 4 shows that the rising position indicating the boundary layer transition point position is greatly different corresponding to the mainstream flow velocity regarded as the Reynolds value as described above, and this boundary layer transition point position is highly sensitive. It is proved to be a number detection parameter. Note that the boundary layer transition point data obtained here can be regarded as corresponding to the Reynolds number because it is understood that the change due to factors other than the Reynolds number is not superimposed in this case.

It is a figure which shows the hollow cylinder which is an example of the measuring method of a boundary layer transition point. It is a figure which shows the two-dimensional blade cross section of the test body used for experiment of this invention. It is a figure which shows the Preston tube used for experiment of this invention. FIG. 4 is a graph showing experimental results demonstrating the correspondence between the Reynolds number and the boundary layer transition position according to the present invention. It is a figure explaining the conventional Reynolds number measurement method using a turbulent sphere.

Explanation of symbols

1 Hollow cylinder 2 Heater 3 Sensor

Claims (7)

  An object with a certain surface state is installed in a wind tunnel, and fluid such as air with constant physical properties such as density, viscosity and kinematic viscosity is used, and the fluid is turbulent and heat transfer is stable. Boundary layer turbulent transition position measured in a certain airflow state in an experiment by previously storing the table as a table of the relationship between the Reynolds number in each airflow state and the boundary layer turbulent transition position on the object surface. A method of obtaining Reynolds number per unit length of fluid in the wind tunnel from data based on the table information.   2. The method according to claim 1, wherein the table information is created in advance from data obtained by measuring the Reynolds number in a certain airflow state and the boundary layer turbulent transition position on the object surface.   2. The table information is created from the boundary layer turbulent transition position predicted from the theory of fluid dynamics under the conditions of the same surface state and shape as the object used for measurement and the Reynolds number and state of the airflow. The method of calculating | requiring the Reynolds number of description.   2. The table information is created from boundary layer turbulent transition positions predicted from computer simulation on condition of the same surface state and shape as an object used for measurement, and Reynolds number and state of airflow. To find the Reynolds number.   The table information is created from the Reynolds number in a certain airflow state and the predicted boundary layer turbulent transition position on the object surface by combining the three methods described in claims 2 to 4. To find the Reynolds number per unit length.   From the Reynolds number R obtained by the method according to claim 1 to 5, when the representative length of the object is L, velocity is U, density is ρ, viscosity is η, and kinematic viscosity is ν, R = [Rho] LU / [eta] = A method for calculating any one of the unknowns among the density [rho], the viscosity [eta], and the kinematic viscosity [nu] based on the relationship expressed by [LU / v].   An object with a certain surface condition is installed in a wind tunnel, and fluid such as air with constant physical properties such as density, viscosity and kinematic viscosity is used. The surface condition of the object of a specific shape, fluid turbulence, and heat transfer In the experiment, data obtained by measuring the boundary layer transition point when another parameter in the state where a predetermined airflow was flowed in a state where two of the parameters were stabilized were previously stored as table information. A method of evaluating one unknown parameter from boundary layer turbulent transition position data of the specific shape measured in the predetermined airflow state.

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