Transient Aerodynamic Heating Research Articles

Experimental study on mechanical behaviors of Al-alloys under transient aerodynamic heating

Determination of mechanical parameters such as the ultimate strength of aerospace materials under the condition of transient heating is critical for reliability evaluation, fatigue life prediction and safety design of high-speed aircrafts including missiles. Al-alloys are widely used as aeronautical materials due to their advantages such as light weight, easy manufacturability and relatively low cost. However, their mechanical properties under transient thermal conditions are not available in the handbooks on material strength, mainly due to the difficulty of simulating the transient thermal conditions for thermal strength test. To solve this problem, a joint thermal–mechanical loading system has been developed in the present investigation to simulate the aerodynamic thermal conditions. The mechanical behaviors of some Al-alloys have been examined with this system. The ultimate strengths and durations of two different types of Al-alloys, i.e. Al7178 and Al2024, under joint thermal–mechanical loading conditions have been tested. Furthermore, their different failure modes and mechanisms under various temperatures have been investigated and compared. These data provide a reliable basis for the study of load bearing capacity and weight reduction of aerospace materials and structures under transient aerodynamic thermal conditions.

High-temperature deformation field measurement by combining transient aerodynamic heating simulation system and reliability-guided digital image correlation

To determine the full-field high-temperature thermal deformation of the structural materials used in high-speed aerospace flight vehicles, a novel non-contact high-temperature deformation measurement system is established by combining transient aerodynamic heating simulation device with the reliability-guided digital image correlation (RG-DIC). The test planar sample with size varying from several mm 2 to several hundreds mm 2 can be heated from room temperature to 1100 °C rapidly and accurately using the infrared radiator of the transient aerodynamic heating simulation system. The digital images of the test sample surface at various temperatures are recorded using an ordinary optical imaging system. To cope with the possible local decorrelated regions caused by black-body radiation within the deformed images at the temperatures over 450 °C, the RG-DIC technique is used to extract full-field in-plane thermal deformation from the recorded images. In validation test, the thermal deformation fields and the values of coefficient of thermal expansion (CTEs) of a chromiumnickel austenite stainless steel sample from room temperature to 550 °C is measured and compared with the well-established handbook value, confirming the effectiveness and accuracy of the proposed technique. The experimental results reveal that the present system using an ordinary optical imaging system, is able to accurately measure full-field thermal deformation of metals and alloys at temperatures not exceeding 600 °C.

The Effect of Nonuniform Surface Temperature on the Transient Aerodynamic Heating of Thin-Skinned Bodies

A quasi-steady analysis is given of the transient forced-convection heating of bodies with thin metallic skins, where the boundary layer is laminar, taking into account the effect of the nonuniform surface-temperature distribution on the rate of heat transfer. LighthiU's approximate theory of heat transfer to a nonisothermal surface is used and leads to a formulation of the problem in terms of a partial integrodifferential equation that is solved in closed form. The results are compared with previous analyses in which the theoretical heat-transfer coefficient for an isothermal surface is used, and it is shown that this latter approximation leads to results in fairly good agreement with the more exact solution. However, if heat-transfer coefficients are calculated from the more exact solution, they may differ greatly from the ones predicted by the isothermal surface theory. This indicates that caution should be exercised in interpreting experimental data obtained by the transient method from a nonisothermal surface where the boundary layer is laminar. INTRODUCTION THE LOCAL RATE OF HEAT TRANSFER t h r o u g h a laminar boundary layer to a semi-infinite flat plate with a uniform surface temperature is well known from boundary-layer theory. For the case of /x and k proportional to the temperature and constant Cp, it is independent of Mach Number and is given by q = 0 .332(f / /«) ' / y( 0. We therefore consider the problem in the following form: bTs(x, t) -A bt zA f x Jz = o d$ Hi>1 (6) r,(o, /) = re Ts(x, 0) = Tt where A, Te, and Tt are constants. Now, Eqs. (6) are invariant under the transformation x' = ax, t' = at. Hence, a solution to these equations of the form Ts = Ts(t/x ^) was sought. This solution was found to be [see Appendix (2) for method of solution]: T — T T ( 5 / 3 ) ( r / * l / 2 ) T Jp. T, 'rWmf^ exp ( « • ' « ) * „ (7a) r { [ r ( 5 / 3 ) ( r / * , / ' ) ] 3 A ; 2 /3 where Ts T, T e Tt Y{m; n -£ r ( 2 / 3 ) exp ( / ) / ' dt (7b) and r = At/G. I t is interesting to compare this solution with tha t obtained by neglecting the effect of temperature gradients—i.e., by approximating the heat transfer through the boundary layer by Eq. (1). The problem then becomes G(dTs/dt) = (A/x ) (Te T8) Ts(0) = Tt The solution to Eq. (8) is Ts Tt ( r or Ts T, Y{r/x ; 1} T. T{ r ( i ) The form (9b) compares with the form (7b). (8)