Study On Data Processing Method And Error Mechanism Analysis Of Heat Flux Measurement In Wind Tunnel

Near space hypersonic vehicles have been highly developed by economic andmilitary powers in recent years. Such vehicles, with complex configurations, canmaneuver for long duration in near space. Slightly or non ablative materials arerequired to maintain the configuration of vehicles. The requirement of configurationmaintenance calls for more strict design of the thermal protection system and moreaccurate prediction of aeroheating environment.Aeroheating testing in the ground based wind tunnels is an important componentto obtain aeroheating environment data of near space hypersonic flight vehicles.Improving the accuracy of the ground based aeroheating measurement is vitallyimportant for the thermal protection system design and the flight safety.In this paper, first of all, the measurement and heat-transfer mechanism of theaeroheating measurement sensors was investigated. By selecting proper mathematicaland physical models, the data processing method, in which the measured sensitivevariables were converted to the heatflux information, was then established. Thereafter,the influence of the data processing method and the heat transfer model on theheatflux measurement was studied. The errors existed in the aeroheating testing werealso analyzed and modified. The work all above can effectively improve the accuracyof the heatflux measurement. At the present time, relevant studies are very few both athome and aboard. In particular, the selection of the heat transfer model of the coaxialthermocouple and its data processing method has not formed an integrated analysissystem. Domestically researches about the influence of the data processing methodand the heat transfer model on the heatflux measurement and about quantitativeanalysis of aeroheating measurement errors are just underway.In order to improve the accuracy of heatflux measurement and to supply the gapof the relevant researches’ shortage, this paper presents the theoretical, numerical andexperimental studies of the aeroheating sensors, the data processing methods and theanalysis and modification of errors. During this work, the data processing softwareabout aeroheating measurement has also been buildup, and consequentially a series ofvaluable results have been obtained:A. Proper mathematical models for the sensor’s heat transfer were selected. Thecomputational method of data processing, in which the measured sensitive variableswere converted to the heatflux information, was then established and validated. It is atheoretical basis for improving the accuracy of the measured heatflux data. i. Based on the structured meshes, the implicit finite volume method ofone-dimensional and axisymmetric heat conduction was established, and thencompared with the three-dimensional explicit finite volume method to support theheat transfer mechanism of the sensors.ii. The computational method of the inverse problem of one-dimensional andaxisymmetric heat conduction was established. The stability and validation of thecomputational method was then performed.iii. The film resistance thermometer can be simplified to one-dimensional heattransfer model and the coaxial thermocouple to axisymmetric. The feasibility of suchsimplification was discussed. The two sensors data processing methods were thenvalidated via numerical simulation on the basis of the actual composition.iv. The applicable range of the material thermophysical parameters inaeroheating testing was defined. The data processing method in large-area aeroheatingtesting was then validated via numerical simulation.B. For verificating data processing methods of typical heatflux sensors, thevalidation experimental program was prepared. Numerical and engineering methodwas used to obtain the surface heatflux distribution on the experimental condition.The results were compared with the processed experimental data to validate the dataprocessing method.i. The experiment program was prepared to validate the data processing method.Several tests were conducted in the shockwave wind tunnel on different inflowconditions for different spheres and hypersonic vehicle. The selected aeroheatingmeasurement techniques included the film resistance thermometer, the coaxialthermocouple and the infrared measurement technique.ii. The sampling data was filtered by the finite impact rejector (FIR), whichcould improve the accuracy and efficiency of the identification.iii. The stagnation heatflux on different experimental conditions for differentspheroids was obtained with the corresponding data processing method for variablesensors.iv. The surface heatflux distribution on the experimental condition for differentspheroids was calculated using the numerical and engineering method, and thencompared with the processed experimental data.C. The influence of the sensors’ mathematical and physical model and dataprocessing method on the heatflux was analyzed. Upon that the difference of theprocessed and actual heatflux was quantitatively presented. The error source ofheatflux measurement was then summarized. Therefore, the uncertainty estimationmethod of aeroheating measurement was established. Finally, improved suggestionsabout the sensor designs and the aeroheating experiments were put forward. i. According to the error characteristic, errors fall into two categories: themodifiable system error and the random error used in uncertainty estimation.ii. The curvature in the stagnation region changes if the sensor is installed. Theflowfield and wall heatflux subsequently changes as well. These changes werediscussed in this paper. The modification method and its coefficient were put forwardfor different type of sensors and different composition of sense organs. Theinterrelation between the temperature rise and the heatflux on the sensor surface wasstudied and thus the modified formula was given to modify the original data.iii. The influence of a small change of the inflow condition on the heatflux wasnumerically analyzed. And the influence of sensors’ random factors, such as the size,the artificially reading, repeated use, on heatflux measurement was analyzed as well.The uncertainty assessment method was shown using the random error analysis theory.The uncertainty of the heatflux measurement in the validation experiment wasobtained via computation.iv. Improved suggestions about the sensor designs and the aeroheatingexperiments were put forward at last.D. The data processing method have been used in heat flux measurement tests ofsome hypersonic vehicles. Software was buildup to obtain the heatflux from filmresistance thermometer and coaxial thermocouple. Multifactor influences wereconsidered to improve the efficiency of aeroheating test.Multiaspects of aeroheating test are involved in this paper. A new dataprocessing method was established, aiming at different aeroheating testing techniques.A new research methodology was put forward to improve the accuracy of aeroheatingmeasurement. The method of data processing, data modification, error analysis anduncertainty and the post processing software are of great value to the accuracy andefficiency of heatflux measurement.