CN111811768B - Recovered enthalpy calibration test piece and wind tunnel thermal assessment method - Google Patents
Recovered enthalpy calibration test piece and wind tunnel thermal assessment method Download PDFInfo
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Abstract
The invention provides a recovery enthalpy calibration test piece and a wind tunnel thermal examination test method, which comprise the steps of designing the recovery enthalpy calibration test piece and obtaining the back temperature change of the concerned part of the test pieceCurve transformation; obtaining a variation curve of the hot wall heat flow on the surface of the test piece along with the wall enthalpy, and obtaining a hot wall heat flow calculation formula through linear fitting; according to the difference between the actual recovery enthalpy of the surface of the test piece and the designed surface recovery enthalpy H, the enthalpy drop influence quantity delta H = H-H caused by water-cooling heat absorption of the spray pipe can be obtained r (ii) a Obtaining a new test enthalpy value newH =2H-H r (ii) a Adjusting the total enthalpy of the airflow at the inlet of the spray pipe to a new test enthalpy value newH, and developing a wind tunnel heating test to ensure that the actual recovery enthalpy of the surface of the examination part reaches a design state. The enthalpy drop influence quantity caused by water cooling heat absorption of the spray pipe is evaluated through the test piece, and a formal examination test state is designed according to the enthalpy drop influence quantity, so that the thermal protection system of the aircraft is truly and effectively examined.
Description
Technical Field
The invention relates to a wind tunnel thermal assessment test method by utilizing electric arcs, and belongs to the technical field of thermal assessment tests.
Background
The development of hypersonic aircraft must first solve the problem of thermal protection. In the current structural thermal protection system research, the selection, the examination and the like of materials are mostly finished by relying on an electric arc wind tunnel, so that a reasonable test state needs to be formulated according to the thermal environment of an area to be examined of an aircraft, and the accurate material level evaluation is realized. It can be said that the electric arc wind tunnel thermal environment test is a key test for determining whether a material can be "last day".
For the material of the aircraft in the large area, a flat thermal examination test is generally adopted, high-temperature air flow generated by an electric arc heater is sprayed out through a leading-out section, a transition section and a rectangular surface spray pipe, a flat model is placed at the outlet of the spray pipe, the flat model and the spray pipe are tightly connected and flush at the front end of the model without a gap, a boundary layer on the model is the natural extension of the boundary layer of the spray pipe wall, and air for heating the flat is the air in the boundary layer of the front spray pipe. To achieve the purpose of temperature resistance examination of the flat test piece, the heat flow and the enthalpy of recovery on the surface of the test piece need to be accurately simulated, wherein the heat flow on the surface of the test piece can be accurately measured by a Gordon meter or a plug type heat flow sensor. But the flat plate test piece is positioned in the boundary layer of the spray pipe, because the spray pipe is cooled by water cooling, the enthalpy drop at the wall surface of the spray pipe is serious due to the heat absorption effect of the water cooling, the recovery enthalpy of the actual flat plate surface is lower than the enthalpy required in the original test state, and the thermal environment of the flat plate surface is in an underassessed state; on the other hand, the enthalpy gradient in the boundary layer is extremely large due to the water-cooling heat absorption of the spray pipe, the total enthalpy sensor has a certain volume, the gas enthalpy value on the surface of the flat test piece cannot be really measured, the enthalpy drop influence quantity caused by the heat absorption of the water-cooling spray pipe is difficult to accurately evaluate, and the authenticity and the effectiveness of a heat check test are seriously influenced.
In the previous flat-plate thermal examination test of the thermal protection material, the actually measured temperature of the surface of a test piece is found to be about 200 ℃ lower than the designed temperature, and the enthalpy drop phenomenon caused by water cooling of the spray pipe has great influence on the temperature. Because the actual thermal examination test piece can not be heated repeatedly, the processing period is long, the price is high, serious time and fund waste is caused once the thermal examination test does not achieve the purpose, and the enthalpy drop influence quantity caused by the water cooling heat absorption of the spray pipe needs to be evaluated in detail before the formal thermal examination test, so as to guide the state design of the formal thermal examination test.
Disclosure of Invention
The invention aims to overcome the defects in the prior art, provides a test piece for evaluating the enthalpy drop influence quantity caused by water cooling heat absorption of a spray pipe, and designs a formal examination test state according to the enthalpy drop influence quantity, so that the thermal protection system of an aircraft can be really and effectively examined.
The technical solution of the invention is as follows:
according to one aspect of the invention, the recovery enthalpy calibration test piece is formed by three layers, wherein an upper layer and a lower layer are made of high-temperature-resistant materials, an intermediate layer is made of heat-insulating materials, and the selection principle of the upper layer material and the lower layer material of the recovery enthalpy calibration test piece is as follows: the surface does not generate the phenomenon of ejecting gas boundary layer caused by gas overflow, the thermophysical parameters and the surface emissivity of the material are clear, and the high temperature resistance temperature is higher than the temperature of the initial design test condition.
Furthermore, the length and the width of the recovery enthalpy calibration test piece are equal to those of an actual test piece.
Furthermore, the upper layer thickness of the enthalpy of recovery calibration test piece is not more than 5mm.
According to another aspect of the invention, a wind tunnel thermal assessment test method implemented by using the recovery enthalpy calibration test piece comprises the following steps:
designing a recovery enthalpy calibration test piece;
carrying out a heating test on the recovery enthalpy calibration test piece by using the initially designed test conditions, and acquiring a back temperature change curve of a concerned part of the recovery enthalpy calibration test piece;
thirdly, performing thermal identification analysis through the recovery enthalpy calibration test piece back temperature curve obtained in the second step to obtain a change curve of the recovery enthalpy calibration test piece surface hot wall heat flow along with the wall enthalpy, and obtaining a hot wall heat flow calculation formula through linear fitting;
step four, comparing and analyzing the hot wall heat flow calculation formula obtained in the step three with the hypersonic boundary layer convection heat exchange formula to obtain recovery enthalpy, and calibrating and measuring the surface recovery enthalpy h of the test piece r And obtaining enthalpy drop influence quantity delta H = H-H caused by water-cooling heat absorption of the spray pipe according to the difference between the actual recovery enthalpy of the surface of the test piece and the designed surface recovery enthalpy H r ；
And fifthly, adjusting the total enthalpy of the airflow at the inlet of the spray pipe to a new test enthalpy value newH = delta H + H, and developing a wind tunnel heating test to ensure that the actual recovery enthalpy of the surface of the examination part reaches a design state.
And the heating time in the second step is determined by the overtemperature damage time of the material, the heating is stopped before the overtemperature damage occurs, and the heating time is as long as possible so as to obtain more data.
In the third step, the calculation formula of the hot wall heat flow obtained by fitting is as follows: q h ＝kh w + b, wherein Q h Is a hot wall heat flow, h w The wall enthalpy, k, b are fitting constants.
In the fourth step, the recovery enthalpy calibration test piece surface hot wall heat flow calculation formula obtained by the hypersonic boundary layer convection heat transfer formula is as follows: q h ＝α(h r -h w ) In the formula, h r To recover enthalpy, α is the convective heat transfer coefficient.
In the fourth step, the recovery enthalpy is used for calibrating the surface recovery enthalpy h of the test piece r The calculating method comprises the following steps: h is a total of r ＝-b/k。
Compared with the prior art, the invention has the beneficial effects that:
(1) According to the method, the recovery enthalpy of the surface of the test piece is corrected and measured through the fitted hot wall heat flow formula and the hypersonic boundary layer convection heat transfer formula, the enthalpy drop influence quantity is calculated, and the problem that the enthalpy drop influence quantity caused by heat absorption of the water-cooling spray pipe is difficult to accurately estimate is solved;
(2) By adopting the test and theoretical analysis means, the invention establishes a mature and reliable enthalpy drop influence quantitative analysis means, and can effectively guide the design of the flat thermal examination test state so as to achieve the purpose of effective examination.
(3) The invention designs the recovery enthalpy calibration test piece, can be repeatedly used, has simple manufacture and low cost, and solves the problems that the actual thermal examination test piece can not be repeatedly heated usually, the processing period is long, the price is high, and the thermal examination test can cause serious time and fund waste once the aim is not achieved.
Drawings
FIG. 1 is a flow chart of the present invention;
FIG. 2 is an installation schematic diagram of an enthalpy calibration test piece for recovery of an electric arc wind tunnel flat plate examination test according to the invention;
FIG. 3 is a schematic view of a recovered enthalpy calibration test piece according to the present invention;
FIG. 4 is a schematic illustration of a recovery enthalpy calibration test piece back temperature curve according to the present invention;
FIG. 5 is a schematic diagram of a back-temperature thermal identification curve of a test piece for enthalpy recovery calibration according to the present invention.
Detailed Description
The present invention will be described in detail with reference to the following examples and accompanying drawings.
According to one aspect of the invention, the recovery enthalpy calibration test piece is formed by three layers, wherein an upper layer and a lower layer are made of high-temperature-resistant materials, an intermediate layer is made of heat-insulating materials, and the selection principle of the upper layer material and the lower layer material of the recovery enthalpy calibration test piece is as follows: the surface of the material does not generate an ejection gas boundary layer phenomenon caused by gas overflow, the thermophysical property parameters and the surface emissivity of the material are clear, the high-temperature resistance temperature is higher than the temperature of the initial design test condition, the length and the width of the recovery enthalpy calibration test piece are equal to those of the actual test piece, and the thickness of the upper layer is not more than 5mm.
In a specific embodiment, the size of the recovery enthalpy calibration test piece is designed based on the size of the formal thermal examination test piece, wherein the length and the width of the recovery enthalpy calibration test piece are consistent with those of the formal thermal examination test piece, the thickness of the upper layer of the test piece is within 5mm, the thickness of the middle layer and the thickness of the lower layer are not required, a schematic diagram of the recovery enthalpy calibration test piece is given in fig. 3, the size of the recovery enthalpy calibration test piece is 100mm × 100mm × 4mm, as shown in fig. 2, a schematic diagram of the installation of the recovery enthalpy calibration test piece of the arc wind tunnel flat plate examination test is given, and the recovery enthalpy calibration test piece and a water-cooling tool of the model support are filled with heat insulation materials and comprise the periphery and the back of the material.
The enthalpy recovery calibration test piece material selection principle comprises the following steps: (1) The surface of the test piece is not damaged in the test process, and the phenomenon of an ejection gas boundary layer caused by the overflow of surface gas is avoided; (2) The thermophysical parameters and the surface emissivity of the material are clear, a high-temperature alloy with clear thermophysical parameters is generally used as a recovery enthalpy calibration test piece material, and the thermocouple is connected to the back of the concerned part of the test piece in a welding mode.
The structure of the formal thermal examination test piece is a part of the original appearance of the test aircraft, and comprises a high-temperature-resistant upper layer, a heat-insulating layer and a lower layer, but the preparation period is long, the cost is high, and the test piece can not be heated repeatedly.
A wind tunnel thermal assessment test method is shown in figure 1 and comprises the following steps:
designing a recovery enthalpy calibration test piece;
step two, carrying out a heating test on the recovery enthalpy calibration test piece by using an initially designed test condition, and obtaining a back temperature change curve of a concerned part of the recovery enthalpy calibration test piece as shown in fig. 4, wherein the test time is determined according to an actual incoming flow state, and on one hand, effective temperature rise data needs to be obtained; on the other hand, if the incoming flow state of the test is severe, the test needs to be stopped before the recovery enthalpy calibration test piece is damaged due to overtemperature, namely, the recovery enthalpy calibration test piece
The initially designed test conditions (known values determined from flight tests) include total enthalpy, temperature.
And step three, correcting and measuring the back temperature curve of the test piece of the recovered enthalpy obtained in the step two, as shown in fig. 4, carrying out thermal identification analysis, and obtaining the hot wall heat flow on the surface of the test piece of the recovered enthalpy correction and measurement. The heat identification is a typical heat conduction inverse problem, which is generally solved by converting the problem into an optimization problem, and the heat flow on the surface of the material is inverted through an efficient optimization algorithm, and the specific process can be referred to documents: ohio Kaifeng, wanqing, qianwei et al, "research review on identification of aerodynamic/thermal parameters of hypersonic aircraft" (J) (Experimental hydrodynamics, 2011,25 (5): 99-104) and Zhang Shiyu, mayuan macro, zhao Jun (research on hypersonic thermal identification technology) (Experimental hydrodynamics, 2013,27 (5): 33-37).
After a recovery enthalpy calibration test piece surface hot wall heat flow changing curve along with wall enthalpy is obtained through a thermal identification method, a hot wall heat flow calculation formula can be obtained through linear fitting:
Q h ＝kh w +b (1)
wherein Q h For hot wall heat flow, h w The wall enthalpy, k, b are fitting constants.
FIG. 5 is a schematic diagram illustrating an example of a back-temperature heat identification curve of a recovery enthalpy calibration test piece, wherein the identified hot-wall heat flow formula is Q h ＝-0.1686h w +166549, corresponding k = -0.1686, b =166549;
step four, comparing and analyzing the hot wall heat flow calculation formula obtained in the step three with the hypersonic boundary layer convection heat exchange formula to obtain recovery enthalpy, and calibrating and measuring the surface recovery enthalpy h of the test piece r And according to the recovery enthalpy, calibrating and measuring the actual recovery enthalpy of the surface of the test piece and the designed surface recovery enthalpy h r The difference can obtain the enthalpy drop influence quantity caused by the water cooling heat absorption of the spray pipeΔH＝H-h r 。
According to the theory of the hypersonic boundary layer, the convection heat exchange formula of the hypersonic boundary layer is as follows:
Q h ＝α(h r -h w ) (2)
wherein Q h For hot wall heat flow, h w Is the enthalpy of wall, h r To recover enthalpy, α is the convective heat transfer coefficient.
Under the condition that the change of the surface convective heat transfer coefficient alpha of the test piece along with the wall temperature is not changed greatly, the heat flow of the hot wall and the wall enthalpy are in a linear relation, so that the calculation formula of the heat flow of the hot wall obtained in the step three and the convective heat transfer formula of the hypersonic boundary layer can be compared and analyzed to solve the actual recovery enthalpy h of the surface of the test piece r As can be seen by comparing the above equations (1) and (2), α (h) r -h w )＝kh w + b, an expression for the recovered enthalpy can be derived from this equation: h is r ＝-b/k；
And step five, overlapping the enthalpy drop influence quantity calculated in the step four to an enthalpy value required by a test state, adjusting the total enthalpy of airflow at the inlet of the spray pipe to a new test enthalpy value newH = H + delta H, developing a wind tunnel heating test, ensuring that the actual recovery enthalpy of the surface of the check piece reaches a design state, and ensuring the authenticity and the coverage of the test state.
Test conditions in the actual test: the total enthalpy is newH and the temperature is the new temperature calculated from the total enthalpy.
Through the steps, the problem of quantitative evaluation of the decrease of the surface enthalpy value of the test piece caused by water cooling of the spray pipe in the arc wind tunnel flat plate test can be solved.
The invention has not been described in detail and is not limited thereto.
Claims (3)
1. A wind tunnel thermal examination test method adopting a recovery enthalpy calibration test piece is characterized by comprising the following steps: the steps are as follows,
designing a recovery enthalpy calibration test piece; the recovery enthalpy calibration test piece is composed of three layers, wherein the upper layer and the lower layer are made of high-temperature-resistant materials, the middle layer is made of heat-insulating materials, and the selection principle of the upper layer material and the lower layer material of the recovery enthalpy calibration test piece is as follows: the surface does not generate an ejection gas boundary layer phenomenon caused by gas overflow, the thermophysical parameters and the surface emissivity of the material are clear, and the high-temperature resistance temperature is higher than the temperature of the initial design test condition;
secondly, carrying out a heating test on the recovery enthalpy calibration test piece by using the initially designed test conditions, and obtaining a back temperature change curve of the concerned part of the test piece;
step three, carrying out thermal identification analysis through the test piece back temperature curve obtained in the step two to obtain a change curve of the hot wall heat flow on the surface of the test piece along with the wall enthalpy, and obtaining a hot wall heat flow calculation formula through linear fitting, wherein the hot wall heat flow calculation formula obtained through fitting is as follows: q h ＝kh w + b, wherein Q h For hot wall heat flow, h w Is the wall enthalpy, k, b are fitting constants;
step four, comparing and analyzing the hot wall heat flow calculation formula obtained in the step three with the hypersonic boundary layer convection heat exchange formula to obtain the surface recovery enthalpy h of the test piece r And according to the difference between the actual surface recovery enthalpy of the test piece and the designed surface recovery enthalpy H, the enthalpy drop influence quantity delta H = H-H caused by the water-cooling heat absorption of the spray pipe can be obtained r The calculation formula of the hot wall heat flow on the surface of the test piece obtained by the convection heat transfer formula of the hypersonic boundary layer is as follows: q h ＝α(h r -h w ) In the formula, h r In order to recover enthalpy, alpha is convective heat transfer coefficient, and the surface recovery enthalpy h of the test piece r The calculation method comprises the following steps: h is r ＝-b/k；
And step five, superposing the enthalpy drop influence quantity delta H obtained in the step four on recovery enthalpy H required by a test state to obtain a new test enthalpy value newH = delta H + H, adjusting the total enthalpy of the airflow at the inlet of the spray pipe to the new test enthalpy value newH, and carrying out a wind tunnel heating test.
2. The wind tunnel thermal assessment test method according to claim 1, characterized in that: and the heating time in the second step is determined by the overtemperature damage time of the material, and the heating is stopped before the overtemperature damage occurs.
3. The wind tunnel thermal assessment test method according to claim 1, characterized in that: the length and the width of the recovery enthalpy calibration test piece are equal to those of an actual test piece, and the thickness of the upper layer of the recovery enthalpy calibration test piece is not more than 5mm.
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