CN-121877333-B - Method and system for measuring Klebanoff stripes in boundary layer

CN121877333BCN 121877333 BCN121877333 BCN 121877333BCN-121877333-B

Abstract

The invention discloses a method and a system for measuring Klebanoff stripes in a boundary layer, and belongs to the technical field of aerodynamic experiment measurement. According to the method, a quasi-wall shear heat film array formed by a plurality of measuring units is laid on a wall to be measured, flow direction quasi-wall shear force and direction expansion quasi-wall shear force distribution are synchronously measured by utilizing two groups of orthogonally-distributed heat film sensing parts in each measuring unit, boundary layer thickness, dynamic viscosity and wall normal reference height are combined, a two-dimensional velocity field near the wall is obtained based on inversion of a boundary layer velocity distribution model, a wall normal vortex vector field is obtained through space difference, and then a transient space structure and a dynamic evolution process of Klebanoff stripes are represented. The method is suitable for boundary layer transition measurement and analysis in wind tunnel experiments, blade profile experiments and blade grid experiments, and can improve the synchronism, reliability and engineering applicability of near-wall small-scale disturbance structure measurement under the condition of complex flow channels.

Inventors

SUN SHUANG
LIU HONGLI
HU XIZHUO
ZHANG FAN
GAO ZIMING

Assignees

中国民航大学

Dates

Publication Date: 20260508
Application Date: 20260323

Claims (12)

1. A method for measuring Klebanoff fringes within a boundary layer, comprising at least the steps of: Under the aerodynamic experiment condition, a quasi-wall shear thermal film array formed by a plurality of measuring units is laid on the wall surface to be tested of an experimental piece, each measuring unit is provided with two groups of thermal film sensing parts which are orthogonally distributed, and a wall surface coordinate system which is unfolded along the flow direction x and the unfolding direction z is established; SS2, supplying power to the thermal film sensing parts of the measuring units and synchronously collecting output signals, and measuring the distribution matrix of the wall flow direction standard wall shearing force tau qx (x, z) and the spreading direction standard wall shearing force tau qz (x, z) according to the orthogonal layout relation of the two groups of thermal film sensing parts of the same measuring unit; SS3, measuring the boundary layer thickness delta of the wall surface to be measured, determining the dynamic viscosity mu of the fluid under the experimental working condition, and giving the normal reference height y of the wall surface; SS4. Inverting to obtain a two-dimensional velocity field near the wall to be measured based on the flow direction quasi-wall shearing force τ qx (x, z), the spanwise quasi-wall shearing force τ qz (x, z) and a preset boundary layer velocity distribution model, wherein the two-dimensional velocity field comprises flow direction velocity u (x, z) and spanwise velocity w (x, z) distribution; SS5, based on the distribution of the two-dimensional velocity field obtained by inversion on the tangential plane x-z of the wall surface to be detected, carrying out space difference calculation through adjacent measuring point data to obtain And (3) with Further obtaining a wall normal vortex vector field w y (x, z), and taking the wall normal vortex vector field as a characterization result of Klebanoff stripes; and SS6, outputting a transient space structure and a dynamic evolution process of Klebanoff stripes on a wall tangent plane x-z to be detected by combining wall normal vortex vector fields w y (x, z) obtained at continuous moments.
2. The method according to claim 1, wherein in step SS1, the quasi-wall shear thermal film array includes a plurality of measurement units formed on the same insulating substrate surface and arranged in an array, each measurement unit includes four thermal film sensing portions electrically independent of each other, each two thermal film sensing portions having a collinear longitudinal centerline form a group, the two groups of thermal film sensing portions are integrally arranged in an orthogonal arrangement, and after the thermal film sensing portions are applied to the wall surface to be tested of the test piece, one group of thermal film sensing portions having a longitudinal centerline oriented in the spanwise z-direction is used for measuring the flow direction quasi-wall shear τ qx (x, z), and the other group of thermal film sensing portions having a longitudinal centerline oriented in the flow direction x-direction is used for measuring the spanwise quasi-wall shear τ qz (x, z).
3. The method according to claim 1 or 2, wherein in step SS1, when the wall surface to be tested of the experimental part is a leaf surface or a curved surface wall surface of a leaf grating, a wall surface coordinate system of the flow direction x and the spanwise z is established according to the local tangential plane geometrical relationship of the wall surface to be tested, then the actual positions of the measuring units on the curved surface wall surface are mapped into the wall surface coordinate system, and in the subsequent steps SS2 to SS6, a two-dimensional shear distribution matrix, a two-dimensional velocity field and a wall surface normal vortex vector field are constructed based on the mapped coordinate positions.
4. The method according to claim 1, wherein in step SS2, power supply and multi-channel synchronous acquisition are performed on the thermal film sensing portion of each measuring unit, the output signals of each measuring point obtained at the same time are converted into the flow direction and the spanwise quasi-wall shearing force of the corresponding measuring point, and a two-dimensional distribution matrix of the flow direction quasi-wall shearing force τ qx (x, z) and the spanwise quasi-wall shearing force τ qz (x, z) is constructed along the flow direction coordinate x and the spanwise coordinate z.
5. The method according to claim 1 or 4, wherein the step SS2 further comprises a thermal film signal conversion step of calibrating the flow direction measuring channel and the direction expansion measuring channel in each measuring unit under the condition of known wall surface shearing force, establishing a conversion relation between the thermal film output signal and the corresponding direction standard wall surface shearing force, and converting real-time output of each thermal film sensing part into the flow direction standard wall surface shearing force and the direction expansion standard wall surface shearing force according to the corresponding conversion relation during subsequent experimental measurement.
6. The method of claim 1, wherein in step SS3, the dynamic viscosity μ is determined according to the fluid temperature under the experimental condition, the wall normal reference height y is selected from the range of the wall normal boundary layer to be measured and satisfies 0< y+.delta.by arranging a pitot tube or a hot wire probe in the upstream incoming flow uniformity region of the wall to be measured, the flow direction velocity profile is measured point by point along the wall normal direction, and the wall normal distance at which the flow direction average velocity reaches 99% of the local outflow velocity is defined as the boundary layer thickness δ.
7. The method according to claim 1, wherein in step SS4, the predetermined boundary layer velocity profile model is: Where u (x, z) is the flow direction velocity distribution, w (x, z) is the spanwise velocity distribution, τ qx (x, z) is the flow direction quasi-wall shear force, τ qz (x, z) is the spanwise quasi-wall shear force, δ is the boundary layer thickness, μ is the dynamic viscosity, and y is the wall normal reference height, and the two-dimensional velocity field distribution near the wall to be measured is obtained accordingly.
8. The method of claim 1, wherein in step SS5, the wall normal vortex flow field w y (x, z) is determined according to the rotation definition of the two-dimensional velocity field in the wall tangential plane x-z to be measured, satisfying the requirement of Wherein And (3) with Calculating by adopting a mode of center difference between adjacent measuring points and one-side difference or interpolation difference of boundary measuring points, and carrying out time sequence reconstruction on w y (x, z) obtained at continuous sampling time to obtain migration, growth and attenuation processes of a wall normal vortex high-value area and a wall normal vortex low-value area in the flow direction and the expansion direction, thereby representing the transient space structure of Klebanoff stripes and dynamic evolution thereof.
9. The method as claimed in claim 1 or 8, wherein in step SS5, the spatial differential calculation is performed by using a central differential method, wherein the flow direction speeds corresponding to the symmetrical measuring points at the positions to be calculated are u 1 and u 2 respectively, the spanwise distances between the two symmetrical measuring points at the positions to be calculated are equal to each other and recorded as Δz, the spanwise speeds corresponding to the symmetrical measuring points at the two sides of the positions to be calculated are w 1 and w 2 respectively, the flow direction speeds corresponding to the two symmetrical measuring points at the positions to be calculated are equal to each other and recorded as Δx, and then there are =(u 2 -u 1 )/(2Δz), = (W 2 -w 1 )/(2Δx), and further find the wall normal eddy current value at that position 。
10. The method according to claim 1, wherein in step SS6, based on the intensity distribution, gradient change or sign alternation characteristics of the wall normal vortex vector field w y (x, z) along the flow direction obtained at successive times, the Klebanoff stripe initial development area, the significant amplification area and the transition completion area in the boundary layer of the wall to be detected are identified, and when the wall normal vortex vector continuously increases along the flow direction and accompanies the encryption of the expansion fluctuation, the corresponding area is determined to be a sensitive area where Klebanoff stripes mainly develop.
11. The method according to claim 1 or 10, wherein in step SS6, the spanwise wavelength, the stripe amplitude, the propagation speed and the spatial growth rate of the stripe are extracted Klebanoff based on the wall normal vortex vector field and the two-dimensional velocity field, the spanwise wavelength is determined according to the spanwise spacing between the peaks or valleys of adjacent stripes at the same flow direction position, the stripe amplitude is determined according to the vortex difference, the propagation speed is determined according to the ratio of the displacement of the characteristic position of the stripe in the flow direction at successive moments to the time interval, and the spatial growth rate is determined according to the variation relation of the disturbance intensity of the stripe at different flow direction positions.
12. A system for measuring Klebanoff fringes in a boundary layer, for implementing a method for measuring Klebanoff fringes in a boundary layer according to any one of claims 1 to 11, comprising at least: The quasi-wall shear thermal film array module is laid on the wall surface to be tested of an experimental piece in an aerodynamic experiment and consists of a plurality of measuring units, and each measuring unit is provided with two groups of thermal film sensing parts in orthogonal layout; The data synchronous acquisition module is in communication connection with the quasi-wall shear thermal film array module and is used for supplying power to the thermal film sensing parts of the measuring units and synchronously acquiring output signals to acquire distribution matrixes of wall flow to be measured to the quasi-wall shear tau qx (x, z) and the spanned quasi-wall shear tau qz (x, z); The two-dimensional velocity field inversion module is in communication connection with the data synchronous acquisition module and is used for acquiring the boundary layer thickness delta of the wall surface to be detected, the dynamic viscosity mu of the fluid under the experimental working condition and the normal reference height y of the wall surface, and inverting to obtain a two-dimensional velocity field containing the flow direction velocity u (x, z) and the spanwise velocity w (x, z) near the wall surface to be detected based on tau qx (x,z)、τ qz (x, z), delta, mu and a preset boundary layer velocity distribution model; the wall normal vortex quantity calculation module is in communication connection with the two-dimensional velocity field inversion module and is used for carrying out space differential calculation through adjacent measuring point data based on the distribution of the two-dimensional velocity field on the tangential plane of the wall to be measured to obtain And (3) with Further obtaining wall normal vortex vector field w y (x, z); The result output module is in communication connection with the wall normal vortex flow calculation module and is used for outputting a transient space structure and a dynamic evolution process of Klebanoff stripes on a wall tangent plane to be detected by combining wall normal vortex flow fields w y (x, z) obtained at continuous moments.

Description

Method and system for measuring Klebanoff stripes in boundary layer Technical Field The invention belongs to the technical field of aerodynamic experiment measurement, relates to a wall surface measurement and characterization technology of a near-wall flow structure in a boundary layer stability experiment, and particularly relates to a measurement method and a measurement system of Klebanoff stripes in a boundary layer, which are suitable for measuring a Klebanoff stripe and other dynamic-change small-scale flow structures and representing transient space distribution and time sequence evolution. Background In aerodynamic experiments and boundary layer stability research, the boundary layer transition process and the identification of a precursor disturbance structure thereof are important basic problems in the design of the appearance of an aircraft, the evaluation of the aerodynamic performance of a blade grid, the control of low choked flow and the experimental research of high-load turbine blades. The Klebanoff strips are taken as a low-frequency band-shaped flow structure for influencing the transition development of the boundary layer, and the measurement of characteristic parameters (such as wavelength, amplitude and propagation speed) is important for understanding the transition mechanism and establishing a transition prediction model. Particularly, in a flat wind tunnel experiment, a blade profile flow around experiment and an engine blade profile aerodynamic experiment, the method effectively measures the dimensions, the strength, the migration characteristics and the time-space evolution law of Klebanoff stripes, and has important significance for revealing a near-wall flow mechanism, checking a numerical calculation result and establishing a transition prediction model. In the existing aerodynamic experiments, measurement means related to boundary layer disturbance mainly comprise a hot wire probe, a wall surface hot film, pressure measurement, an optical flow field diagnosis means and the like. Conventional thermal film sensors are only sensitive to flow along the normal of their sensing portion and therefore typically only measure shear forces in an effective single flow direction. When the flow is a complex three-dimensional flow, the wall shear force is a two-dimensional vector having both flow direction and spanwise components. The two-direction component information cannot be obtained simultaneously by using the traditional unidirectional thermal film, if the measurement is carried out by the rotary sensor, transient synchronous data cannot be obtained, the operation is complex, and the spatial resolution is reduced. At present, although research is attempted to measure the flow velocity of a space point by using a cross double-wire or three-wire hot wire probe, the probe has a large volume, is difficult to be arranged close to a wall surface, and is mainly used for measuring the three-dimensional flow velocity vector of the space point, but not used for measuring the two-dimensional shear vector of the wall surface. Meanwhile, the probe generally has the characteristics of overhanging of a supporting structure, limited clearance between a measuring body and a wall, higher requirements on the posture control of the probe and the like, and the problems of insufficient installation space, difficult near-wall arrangement and additional disturbance to an original flow field often exist in aerodynamic experiments of a narrow flow channel, a curved wall surface, a rotating blade grid adjacent area and the like. In addition, klebanoff stripes are used as a speed disturbance to influence the development of a boundary layer, but a single observation means of Klebanoff stripes can only be observed through an optical means for a long time, but the means needs an open light path space, is difficult to be applied in a complex flow channel, and has the problem of lower resolution in an engine blade grid environment with smaller scale. Meanwhile, the existing partial measurement mode focuses on the outer layer speed field or the whole flow form, the corresponding relation between the disturbance structure near the wall surface and the wall surface response is revealed to be insufficient, and the requirements of developing the fine measurement and analysis on the boundary layer transition precursor structure are difficult to meet. In summary, the measurement means for the boundary layer Klebanoff stripes under the existing aerodynamic experiment conditions still have defects in the aspects of near-wall area applicability, complex flow channel arrangement capability, transient synchronous measurement capability, high space-time resolution characterization capability and the like. Therefore, how to build a technology which can be applied to the near-wall area of the boundary layer, is convenient to implement in the limited space and the complex flow channel environment and can effectively measure the str