CN112393876B - Dynamic pneumatic derivative prediction method suitable for internal and external flow integrated appearance - Google Patents
Dynamic pneumatic derivative prediction method suitable for internal and external flow integrated appearance Download PDFInfo
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- CN112393876B CN112393876B CN201910756444.0A CN201910756444A CN112393876B CN 112393876 B CN112393876 B CN 112393876B CN 201910756444 A CN201910756444 A CN 201910756444A CN 112393876 B CN112393876 B CN 112393876B
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Abstract
The invention provides a dynamic pneumatic derivative prediction method suitable for an internal and external flow integrated appearance, which comprises the steps of calculating dynamic derivative data D1 of an aircraft in each direction under real frequency; calculating corresponding data of the dynamic derivatives at the frequency to be selected, comparing the data with standard data one by one, selecting a group with the minimum difference as D2, recording the corresponding frequency as f, and obtaining the difference delta D1 of the dynamic derivatives; acquiring dynamic derivative data D3 of the test model under the frequency f through a wind tunnel experiment; calculating dynamic derivative data D4 of the test model after scaling under the frequency f to obtain a difference value delta D2 of the dynamic derivative caused by the scaling of the model; judging the values of the delta D1/D1 and the delta D2/D1 until the threshold requirements are met, and then calculating modified dynamic derivative data D according to the values of D1, D2 and D3; the invention solves the problem of large difference between the heaven and earth of the dynamic derivative data in the prior art.
Description
Technical Field
The invention relates to a dynamic pneumatic derivative calculation method, and belongs to the technical field of dynamic pneumatic derivative calculation.
Background
The dynamic aerodynamic derivative is generally called as a 'dynamic derivative' in engineering and is an important input parameter required by aircraft control law design and flight quality analysis. Early aircraft were mostly flying at small angles of attack and zero sideslip, and usually the aerodynamic coefficient varied linearly with the angle of attack, and the dynamic derivative could be seen as a constant. With the development of aerospace technology, the flight state of a modern aircraft changes, large power angle and non-zero sideslip flight become normal, the flight state of the aircraft causes a complex unsteady phenomenon, the dynamic derivative is no longer constant, but forms a nonlinear relation with flight parameters, and in some cases, small changes of the flight parameters may cause changes of the magnitude of the dynamic derivative, even changes of the sign. Particularly, in recent years, a high-speed aircraft has a large flight envelope span and a fast flight state change, and is smaller than the inherent dynamic stability of a conventional aircraft, and faces the challenges of insufficient flight internal stability and control force, mainly related to the dynamic characteristics of the transverse course, serious transverse lateral dynamic instability and coupling problems may exist, but in the current dynamic derivative test, due to the limitation of the size of wind tunnel equipment, the aircraft needs to perform an equal-proportion scaling with a scaling scale of about dozens to normally perform a wind tunnel test, so that the wind tunnel test model has a smaller size, particularly the size of an inner runner is smaller, so that inflow flow cannot be truly simulated, due to the limitation of the frequency of a motor in the wind tunnel equipment, the aircraft can only simulate in a frequency range of 6-18 HZ, and the frequency range of the aircraft in actual flight exceeds the frequency range, the dynamic motion cannot be truly simulated, and the dynamic derivative data obtained by the method has large day-to-ground difference.
At present, a set of feasible and applicable dynamic aerodynamic derivative high-precision prediction method for coupling internal flow and external flow is not established in the wind tunnel test technology in China, and the wind tunnel test technology in the aspect needs to be broken through urgently.
Disclosure of Invention
The invention aims to overcome the defects in the prior art, provides a dynamic pneumatic derivative prediction method suitable for an internal and external flow integrated shape, and solves the problem that the existing dynamic pneumatic derivative calculation has large space-to-ground difference.
The technical solution of the invention is as follows:
a dynamic pneumatic derivative prediction method suitable for an internal and external flow integrated shape comprises the following steps:
acquiring the real frequency of the aircraft to be tested under the Mach number to be tested according to the flight trajectory of the aircraft;
modeling the aircraft, calculating the dynamic derivative data of the aircraft in all directions under real frequency, and taking the data as standard data D1;
selecting n frequencies to be tested according to the limit range of the wind tunnel on the test simulation frequency, calculating the data corresponding to the dynamic derivative under the frequency to be selected, wherein n groups are calculated, comparing n groups of data with standard data D1 one by one, selecting one group with the minimum difference as D2, recording the frequency corresponding to the group of dynamic derivative data as f, and obtaining the difference delta D1 of the dynamic derivative caused by different frequencies as D1-D2;
based on the current situation of the existing hypersonic wind tunnel test equipment, a scaling ratio 1 meeting the requirements of a wind tunnel test is designed: the method comprises the following steps that (1) an M aircraft test model obtains dynamic derivative data of the test model under the frequency f through a wind tunnel experiment, and the data are used as basic data D3 of the dynamic derivative of the aircraft;
modeling the aircraft test model after scaling, calculating dynamic derivative data D4 at the frequency f, and obtaining the difference value delta D2 of the dynamic derivatives caused by the model scaling, namely D1-D4;
judging the values of delta D1/D1 and delta D2/D1, if the obtained values are both smaller than the threshold value, carrying out the next step, if the obtained delta D1/D1 value is larger than or equal to the threshold value, returning to reselect the frequency to be detected, recalculating delta D1/D1 until the delta D1/D1 is smaller than the threshold value, and recalculating delta D2/D1; if the obtained delta D2/D1 value is larger than or equal to the threshold value, returning to the test model after the scaling is corrected, and recalculating delta D2/D1; if the values of the delta D1/D1 and the delta D2/D1 are both larger than or equal to the threshold value, returning to the frequency to be measured again, recalculating the delta D1/D1 until the value of the delta D1/D1 is smaller than the threshold value, and recalculating the delta D2/D1;
the value of the corrected aircraft dynamic derivative data D is based on:
if Δ D1>0 and Δ D2>0, D3+ Δ D1+ Δ D2;
if Δ D1>0 and Δ D2<0, then D3+ Δ D1;
if Δ D1<0 and Δ D2>0, D3+ Δ D2;
if Δ D1<0 and Δ D2<0, then D — D3.
Further, the threshold value is delta D1/D1< 5%, and delta D2/D1< 20%.
Compared with the prior art, the invention has the beneficial effects that:
(1) according to the method, the simulation data and the experimental data are combined, the data of the wind tunnel test are corrected, the high-precision dynamic derivative data are obtained, and the difference between the heaven and the earth of the dynamic derivative is reduced;
(2) according to the method, the problem that the real frequency is not in the limit range of the wind tunnel on the test simulation frequency when the dynamic derivative data is solved through the determination of the frequency f in the wind tunnel experiment is solved, and the calculation precision of the dynamic derivative is improved.
Drawings
FIG. 1 is a flow chart of a dynamic aerodynamic derivative prediction method for an internal and external flow integrated profile according to the present invention;
Detailed Description
The present invention will be described in detail with reference to the following examples and accompanying drawings.
As shown in fig. 1, a dynamic aerodynamic derivative prediction method suitable for an internal and external flow integrated profile includes the following steps:
step one, acquiring the real frequency of the aircraft to be tested under the Mach number to be tested according to the flight trajectory of the aircraft, which is a known technology in the field;
step two, modeling the aircraft by using software, calculating the dynamic derivative data of the aircraft in each direction under the real frequency, and taking the data as standard data D1, which is a technique known in the art;
selecting n to-be-selected frequencies according to the limit range of the wind tunnel on the test simulation frequency, calculating the data corresponding to the dynamic derivative under the to-be-selected frequencies by using software, wherein n groups of data are compared with standard data D1 one by one, selecting one group with the minimum difference value as D2, recording the frequency corresponding to the group of dynamic derivative data as f, and obtaining the difference value delta D1 of the dynamic derivative caused by different frequencies as D1-D2;
step four, designing a scaling ratio 1 meeting the requirements of the wind tunnel test based on the current situation of the existing hypersonic wind tunnel test equipment: m aircraft test models, acquiring dynamic derivative data of the aircraft test models under the frequency f through wind tunnel experiments according to the frequency f determined in the step three, wherein the data is used as basic data D3 of the dynamic derivatives of the aircraft;
step five, modeling the scaled aircraft test model by using software, and calculating dynamic derivative data D4 at the frequency f, which is a technology known in the art, and obtaining the difference value delta D2 of the dynamic derivatives caused by model scaling as D1-D4;
step six, judging the values of the delta D1/D1 and the delta D2/D1,
if the obtained delta D1/D1 value is less than 5 percent and the obtained delta D2/D1 value is less than 20 percent, performing a seventh step;
if the obtained value of delta D1/D1 is larger than or equal to 5%, returning to reselect the frequency to be measured, recalculating delta D1/D1 until the value of delta D1/D1 is smaller than the threshold value, recalculating delta D2/D1, and if the value of delta D2/D1 is smaller than 20%, performing step seven;
if the obtained value of delta D2/D1 is larger than or equal to the threshold value, returning to the test model after the scaling is corrected, wherein the modification of the test model generally comprises the steps of modifying the air inlet channel according to engineering experience, recalculating delta D2/D1 until the value of delta D2/D1 is smaller than 20%, and then performing step seven;
if the values of the delta D1/D1 and the delta D2/D1 are both larger than or equal to the threshold value, returning to the frequency to be measured again, recalculating the delta D1/D1 until the value of the delta D1/D1 is smaller than the threshold value, recalculating the delta D2/D1 until the value of the delta D2/D1 is smaller than 20%, and then performing step seven;
the threshold value is selected according to engineering experience, 5% and 20% of the threshold value can meet the precision requirement, if the threshold value is too large, the precision of the dynamic derivative is possibly insufficient, if the threshold value is too small, the calculation times of the data of the dynamic derivative are possibly too many, the calculation is complicated due to too many correction times, and the consumed time is too long.
Step seven, the value of the modified dynamic derivative data D is as follows: if Δ D1>0 and Δ D2>0, D3+ Δ D1+ Δ D2; if Δ D1>0 and Δ D2<0, then D3+ Δ D1; if Δ D1<0 and Δ D2>0, D3+ Δ D2; if Δ D1<0 and Δ D2<0, then D — D3.
In other embodiments, the invention may be implemented in a different order and still fall within the scope of the invention.
The invention has not been described in detail and is in part known to those of skill in the art.
Claims (2)
1. A dynamic pneumatic derivative correction method is characterized by comprising the following steps:
acquiring the real frequency of an aircraft to be measured under the Mach number to be measured;
step two, calculating the dynamic derivative data of the aircraft in each direction under the real frequency, and taking the data as standard data D1;
selecting n frequencies to be selected, calculating data corresponding to the dynamic derivative at the frequencies to be selected by using software, wherein n groups are obtained, comparing n groups of data with standard data D1 one by one, selecting one group with the minimum difference value, and marking the group as D2, wherein the frequency corresponding to the group of data of the dynamic derivative is marked as f, and obtaining the difference value delta D1 of the dynamic derivative caused by different frequencies as D1-D2;
designing a scaling ratio 1 which meets the requirements of wind tunnel tests: the method comprises the following steps that (1) an M full-projectile test model obtains dynamic derivative data of the test model under the frequency f through a wind tunnel test, and the data are used as basic data D3 of the dynamic derivative of the aircraft;
calculating dynamic derivative data D4 of the test model after scaling under the frequency f, and obtaining the difference value Delta D2 of the dynamic derivatives caused by the model scaling as D1-D4;
step three, judging the values of the delta D1/D1 and the delta D2/D1, if the obtained values are both smaller than the threshold value, carrying out the next step, if the obtained delta D1/D1 value is larger than or equal to the threshold value, returning to reselect the frequency to be selected, recalculating the delta D1/D1 until the delta D1/D1 is smaller than the threshold value, and recalculating the delta D2/D1; if the obtained delta D1/D1 value is smaller than the threshold value and the obtained delta D2/D1 value is larger than or equal to the threshold value, returning to the test model after the scaling is corrected, and recalculating delta D2/D1;
step four, the value of the modified dynamic derivative data D is based on: if Δ D1>0 and Δ D2>0, D3+ Δ D1+ Δ D2; if Δ D1>0 and Δ D2<0, then D3+ Δ D1; if Δ D1<0 and Δ D2>0, D3+ Δ D2; if Δ D1<0 and Δ D2<0, then D — D3.
2. The dynamic pneumatic derivative correction method according to claim 1, characterized in that: the threshold values are Delta D1/D1< 5%, and Delta D2/D1< 20%.
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