CN112784360A - Constant blowing and sucking method for weakening aerodynamic optical effect of turbulent boundary layer - Google Patents
Constant blowing and sucking method for weakening aerodynamic optical effect of turbulent boundary layer Download PDFInfo
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Abstract
The invention belongs to the field of crossing of aerodynamics and optical engineering, and discloses a constant blowing and sucking method for weakening the aerodynamic optical effect of a turbulent boundary layer. The method comprises three steps of determining a blowing and sucking disturbance function form, giving a function variable specific form and parameter, and giving a function variable specific form and parameter. Compared with the traditional unsteady blowing and sucking control scheme, the method is efficient and feasible, and has reference value for turbulent boundary layer phenomenon research based on flow control and optical imaging guidance aircraft design.
Description
Technical Field
The invention relates to the interdisciplinary field of aerodynamics and optical engineering, and the method is suitable for problems of turbulent boundary layer flow mechanism research, optical imaging guidance aircraft design and the like.
Background
The flow field near the viewing window becomes extremely complex when the imaging guided vehicle is flying at high speeds in the atmosphere. Due to the fact that the Mach number and the Reynolds number are high, the head of the aircraft can form a shock wave structure, and turbulent boundary layers, shear layers and the like can be generated by flow near the window. When a high-speed aircraft with an Optical imaging guidance system flies in the atmosphere, a complex flow field is formed between an Optical hood and an incoming flow, thermal radiation and image transmission interference are caused to an Optical imaging detection system, and target image deviation, jitter, blurring and imaging intensity reduction are caused, and the Effect is called an aerooptical Effect (Aero-Optical Effect). With the development of accurate guidance requirements, the aerooptical phenomenon is gradually emphasized by various aerospace major countries, and the application background of the aerooptical phenomenon in the military field is particularly obvious. The precision and timeliness of information acquisition of the precise striking weapon depend on the degree of the precision and timeliness, so that the adoption of an optical imaging detection tracking technology becomes a necessary trend for development of precise striking. Compared with the traditional inertial guidance, instruction guidance and wireless terminal guidance, the optical detection mode has the characteristics of high precision and strong anti-interference capability.
From the view point of crossing aerodynamics and optical engineering, the research objects of the pneumatic optics are mainly the influence of wall flow, mixed layers, bosses and the like on light deflection and optical path distribution. The light ray is transmitted in the flow field, and the relation between the density rho of the flow field and the refractive index n of the gas is calculated by the following relational expression
n＝1+ρKGD
KGD(unit: m)3/kg) is the Gladstone Dale constant, determined by the wavelength λ of the light. The Optical Path Length (OPL) is defined as the integral of the refractive index along the z propagation direction of the Optical axis
The Optical Path Difference (OPD) reflects the degree of wavefront distortion, and is defined as
OPD(x,y,t)＝OPL(x,y,t)-<OPL(x,y,t)>
Where < OPL (x, y, t) > is the spatial averaging operation in the pupil plane. How to weaken the pneumatic optical effect and improve the imaging guidance detection precision is an urgent problem to be solved, and has strong academic research and engineering application values.
Turbulent boundary layers caused by flat plate flow are common physical models in the engineering field and have important research significance, but at present, researches for weakening the pneumatic optical effect based on a flow control method are very rare. White et al published in 2013 at the 51 st AIAA aerospace science conference on the general Investigation of Wall painting and surgery in a transnic Boundary Layer, indicating that Wall Suction may achieve reduced aerodynamic optical effects, but that the non-constant Suction model is less efficient. In the Journal of turbulences Journal published in 2020 by Sun Xiwan, the method points out that the turbulent boundary layer can be controlled to enter the laminar state by adopting the unsteady air extraction with proper intensity, and the flow field result needs to be reasonably predicted and is difficult to implement; or strong unsteady pumping disturbance is adopted, although a turbulent structure reappears downstream, the potential of reducing the pneumatic optical effect is also realized, but the larger amplitude is required and the efficiency is lower. In general, the adoption of unsteady suction to achieve boundary layer aerodynamic optical attenuation requires reasonable prediction of strength, or is inefficient and less feasible. Therefore, there is an urgent need to develop an effective operation method for reducing the aerodynamic optical effect of the turbulent plate boundary layer. There are three main types of blowing and sucking disturbances, namely blowing and sucking, single blowing and single sucking disturbances.
Disclosure of Invention
The invention aims to solve the technical problem that a steady blowing and sucking disturbance method is provided as an effective and feasible method aiming at the defects of the prior art, and the problem of the aerodynamic optical effect of a weakened turbulent flat plate boundary layer is solved.
The specific technical scheme of the invention is as follows:
a constant blowing and sucking method for weakening the aerodynamic optical effect of a turbulent boundary layer comprises the following steps:
step 1: determining a blowing and sucking disturbance function form
Considering flow direction position, span direction position and time effect when giving blowing and sucking disturbance of a flat plate boundary layer, setting the flow direction position, the span direction position and the time effect as required to be in a constant or constant form, and selecting the following functional form to realize the blowing and sucking disturbance:
vbs＝Au∞f(x)g(z)h(t)
wherein v isbsIndicating the speed of the disturbance, subscripts b and s are the initials of blowing and suction, respectively, A is the amplitude of the applied disturbance, u∞Is the incoming flow velocity, f (x), g (z), and h (t) are the flow phase, the spanwise phase, and the time term, respectively;
based on the blowing and sucking disturbance function, the blowing and sucking speeds are v respectively for a single blowing or sucking disturbancebAnd vsAnd directly taking an absolute value to determine:
vb＝2|Au∞f(x)g(z)h(t)|
vs＝-2|Au∞f(x)g(z)h(t)|
where the formula top multiplied by 2 indicates that the amplitude remains at a because the function would halve the amplitude when taking the absolute value;
step 2: given function variable specific forms and parameters
In step 2A is adjustable, f (x) and g (z) are given as
f(x)＝4sin(θ)[1-cos(θ)]/(27)1/2
θ＝2π(x-xst)/(xed-xst)
Wherein x and z are flow direction position coordinates; theta is an intermediate variable of the flow direction phase function, xstAnd xedIndicating the start and stop of blowing and sucking disturbance in the flow directionA position coordinate; l is the number of the marked disturbance wave number in the spanwise phase function, lmax＝10，ZlIs the contribution ratio, z, corresponding to each perturbation wave numbermaxIs the width of the spanwise computation field, philIs a group of [0,1]The random number of (2); for the f (x) function of each blowing and sucking disturbance point, firstly, according to the local flow direction position x and the coordinate x of the blowing and sucking disturbance at the start and stop position of the flow directionstAnd xedCalculating the theta phase value, and then calculating the sub-function value by using a function expression f (x); for each blowing and sucking disturbance point, the function of g (z) is givenmaxCalculate each ZlValues, and then g (z) function expressions to calculate this sub-function value; returning the function values of f (x) and g (z) to the blowing and sucking disturbance master function, namely returning to the v in the step 1bsIn the expression and according to the given amplitude A of the applied disturbance and the incoming flow velocity u∞Calculating the applied disturbance velocity vbs；
And step 3: applying a blowing and sucking disturbance function to a laminar flow section
Applying a blowing and sucking disturbance function to a wall surface normal velocity v of the laminar flow section, namely v ═ vbOr vsReplacing v-0 at the original wall to control flow; the wall surface speed is used as a boundary condition, updating is carried out once at each time step during calculation, and the downstream pneumatic optical effect is analyzed during calculation.
Compared with the prior art, the method realizes the constant blowing and sucking control of the turbulent flat boundary layer, can effectively weaken the pneumatic optical effect value of a turbulent area within a larger control intensity range, and adopts the principle of suppressing the development of flowing non-constant vortex through constant disturbance. Compared with the traditional unsteady blowing and sucking control scheme, the method is efficient and easy to implement.
Drawings
FIG. 1 is a flow chart of the inventive scheme;
FIG. 2 is an ensemble mean wall normal velocity profile of the constant and unsteady blow/suction perturbation methods at the blow-suction stage;
FIG. 3 is a comparison of density clouds illustrating spanwise symmetry of steady and unsteady puff perturbations with an amplitude A of 0.15 and steady and unsteady inhale perturbations with an amplitude A of 1.0;
figure 4 is a histogram of the values of the constant and unsteady insufflation/insufflation perturbation aerodynamic optical effects.
Detailed Description
The invention is further described with reference to the following figures and specific examples.
Step 1: determining a blowing and sucking disturbance function form
Considering flow direction position, span direction position and time effect when giving blowing and sucking disturbance of a flat plate boundary layer, setting the flow direction position, the span direction position and the time effect as required to be in a constant or constant form, and selecting the following functional form to realize the blowing and sucking disturbance:
vbs＝Au∞f(x)g(z)h(t)
where v denotes the normal wall velocity, subscripts b and s are the initials for blowing and suction respectively, A is the amplitude of the applied disturbance, u∞Is the incoming flow velocity, f (x), g (z), and h (t) are the flow phase, the spanwise phase, and the time unsteady terms, respectively;
based on the blowing and sucking disturbance function, the blowing and sucking speeds are v respectively for a single blowing or sucking disturbancebAnd vsAnd directly taking an absolute value to determine:
vb＝2|Au∞f(x)g(z)h(t)|
vs＝-2|Au∞f(x)g(z)h(t)|
where the formula top multiplied by 2 indicates that the amplitude remains at a because the function would halve the amplitude when taking the absolute value;
step 2: given function variable specific forms and parameters
In step 2A is the adjustable amplitude, f (x) and g (z) are given as
f(x)＝4sin(θ)[1-cos(θ)]/(27)1/2
θ＝2π(x-xst)/(xed-xst)
Wherein x and z are flow direction position coordinates; theta is an intermediate variable of the flow direction phase function, xstAnd xedRepresenting the start-stop position coordinates of the blowing and sucking disturbance in the flow direction; l is the number of the marked disturbance wave number in the spanwise phase function, lmax＝10，ZlIs the contribution ratio, z, corresponding to each perturbation wave numbermaxIs the width of the spanwise computation field, philIs a group of [0,1]The random number of (2); for the f (x) function of each blowing and sucking disturbance point, firstly, according to the local flow direction position x and the coordinate x of the blowing and sucking disturbance at the start and stop position of the flow directionstAnd xedCalculating the theta phase value, and then calculating the sub-function value by using a function expression f (x); for each blowing and sucking disturbance point, the function of g (z) is givenmaxCalculate each ZlValues, and then g (z) function expressions to calculate this sub-function value; returning the function values of f (x) and g (z) to the blowing and sucking disturbance master function, namely returning to the v in the step 1bsIn the expression and according to the given amplitude A of the applied disturbance and the incoming flow velocity u∞Calculating the applied disturbance velocity vbs；
φlThe value for each (x, z) position is time invariant throughout the simulation process, so as not to introduce spurious time anomalies; and for constant blowing and sucking, h (t) taking a constant value; in theory, h (t) can be any given positive number, and the product of h (t) and the amplitude A together reflect the disturbance intensity, and h (t) in this embodiment is selected to be 0.245 to ensure that the blowing or inhaling intensity is equal to the time-invariant intensity obtained by h (t) in the literature, Aero-optical compression for super particulate turbine boundary layer (Sun Xiwan et al, 2020, Journal of turbulences), and to ensure comparability.
And step 3: applying a blowing and sucking disturbance function to a laminar flow section
Applying a blowing and sucking disturbance function to a wall surface normal velocity v of the laminar flow section, namely v ═ vbOr vsReplacing v-0 at the original wall to control flow; taking the wall surface speed as a boundary condition, updating once at each time step during calculation, and analyzing the downstream in the calculationAerodynamic optical effects.
When a numerical simulation method is adopted to solve the flow field development and the downstream pneumatic optical effect, if unsteady blowing/suction disturbance is adopted, the wall surface boundary layer condition is updated during each time of calculation of the pushing progress. When the constant insufflation/inspiration perturbation of the present invention is employed, only the perturbation value at the initial moment needs to be given.
In numerical simulation, the pneumatic optical effect of the pupil at a certain position downstream is calculated, and the comparison with the traditional unsteady blowing/inspiration disturbance can illustrate the rationality of the invention, and the comparison is as follows. Based on physical models and boundary conditions, Ma, used in numerical simulation∞＝2.9、T∞170K respectively represent the mach number and the static temperature of the incoming flow, wherein the blowing and sucking disturbance function is applied to the laminar flow section, the calculation calculated by the demonstration of the relevant numerical simulation method is shown in the first four columns of the following table 1 (wherein Baseline represents the calculation example when no disturbance is applied), and the blowing and sucking disturbance application range is the flow direction coordinate xst5.5 and xedLaminar flow region of 6.0. When the constant blowing/breathing disturbance h (t) is 0.245, the wall normal disturbance amplitude of the time-averaged value is very close to the non-constant example (see fig. 2), and the constant and non-constant examples are obviously comparable. Fig. 3 shows a density cloud chart of a spanwise symmetric plane of the constant and unsteady blowing disturbances with an amplitude a of 0.15 and the constant and unsteady suction disturbances with an amplitude a of 1.0, and it can be seen that when the constant blowing/suction disturbances are applied to the upstream laminar flow section, even if the disturbance amplitude is large, the flow field in the calculation domain is relatively stable, and the unsteady effect is much smaller than that of the unsteady blowing-suction scheme.
TABLE 1
FIG. 4 shows the calculation results of the time-averaged aero-optical effect for each set of calculations, and the time-averaged OPD for an unsteady blowing/suction versus an unsteady regime is shown in the last column of the tablermsThe value changes. It can be seen that the steady-state scheme can make the aerodynamic optical effect slightly reduced when the blowing and suction disturbance amplitude is small, but the amplitude is smallWhen the value is larger, a more obvious effect can be produced. It is important to highlight that when steady inspiration disturbance is adopted, increasing the disturbance amplitude does not cause the downstream flow field to recover the turbulent state, and the pneumatic optical effect weakening can be realized in a larger amplitude range.
In summary, the use of constant blowing/suction turbulence allows the reduction of the aerodynamic optical effect over a large amplitude range, by controlling the steady effect of the pressing flow constantly. The invention has reference value for turbulent boundary layer phenomenon research based on flow control and optical imaging guidance aircraft design.
While the invention has been described in detail and with reference to the specific embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments, but may be modified in various forms and details by those skilled in the art. The invention is not to be considered as limited to the specific embodiments thereof, but is to be understood as being modified in all respects, all changes and equivalents that come within the spirit and scope of the invention.
Claims (1)
1. A constant blowing and sucking method for weakening the aerodynamic optical effect of a turbulent boundary layer is characterized by comprising the following steps:
step 1: determining a blowing and sucking disturbance function form
Considering flow direction position, span direction position and time effect when giving blowing and sucking disturbance of a flat plate boundary layer, setting the flow direction position, the span direction position and the time effect as required to be in a constant or constant form, and selecting the following functional form to realize the blowing and sucking disturbance:
vbs＝Au∞f(x)g(z)h(t)
wherein v isbsIndicating the speed of the disturbance, subscripts b and s are the initials of blowing and suction, respectively, A is the amplitude of the applied disturbance, u∞Is the incoming flow velocity, f (x), g (z), and h (t) are the flow phase, the spanwise phase, and the time term, respectively;
based on the blowing and sucking disturbance function, the blowing and sucking speeds are v respectively for a single blowing or sucking disturbancebAnd vsAnd directly taking an absolute value to determine:
vb＝2|Au∞f(x)g(z)h(t)|
vs＝-2|Au∞f(x)g(z)h(t)|
where the formula top multiplied by 2 indicates that the amplitude remains at a because the function would halve the amplitude when taking the absolute value;
step 2: given function variable specific forms and parameters
In step 2A is adjustable, f (x) and g (z) are given as
f(x)＝4sin(θ)[1-cos(θ)]/(27)1/2
θ＝2π(x-xst)/(xed-xst)
Wherein x and z are flow direction position coordinates; theta is an intermediate variable of the flow direction phase function, xstAnd xedRepresenting the start-stop position coordinates of the blowing and sucking disturbance in the flow direction; l is the number of the marked disturbance wave number in the spanwise phase function, lmax＝10，ZlIs the contribution ratio, z, corresponding to each perturbation wave numbermaxIs the width of the spanwise computation field, philIs a group of [0,1]The random number of (2); for the f (x) function of each blowing and sucking disturbance point, firstly, according to the local flow direction position x and the coordinate x of the blowing and sucking disturbance at the start and stop position of the flow directionstAnd xedCalculating the theta phase value, and then calculating the sub-function value by using a function expression f (x); for each blowing and sucking disturbance point, the function of g (z) is givenmaxCalculate each ZlValues, and then g (z) function expressions to calculate this sub-function value; returning the function values of f (x) and g (z) to the blowing and sucking disturbance master function, namely returning to the v in the step 1bsIn the expression and according to the given amplitude A and A of the applied disturbanceVelocity u of incoming flow∞Calculating the applied disturbance velocity vbs；
And step 3: applying a blowing and sucking disturbance function to a laminar flow section
Applying a blowing and sucking disturbance function to a wall surface normal velocity v of the laminar flow section, namely v ═ vbOr vsReplacing v-0 at the original wall to control flow; the wall surface speed is used as a boundary condition, updating is carried out once at each time step during calculation, and the downstream pneumatic optical effect is analyzed during calculation.
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