Simulation of flutter suppression for a transonic fan blade based on plasma excitation

Along with the development of advanced high-performance aero-engines to the higher thrust-weight ratio, further improvement of stage load, the adoption of new materials and new lightweight structures, the aeroelasticity of blade structure is becoming more and more prominent. The high cycle fatigue failure of blades significantly reduces the structural reliability during the process of development and using. At the same time, a large number of failure forms of aero-engine experimental and server can be attributed to aeroelastic problems. Therefore, it is urgent to improve the aeroelastic stability of the blade. One of the most important factors is to suppress the airflow separation, but its mechanism is still unclear. Based on this, this paper combines the aerodynamic damping analysis of energy method with the plasma excitation simulation and references low-speed wind tunnel plasma expansion test to consider the effects of different exciter distributions and intensities on flutter. The results show that stall flutter is related to the flow separation, but the flow separation is not a key factor that determinates whether the flutters occurs or not. Flutter suppression is strongly correlated with the shock wave intensity, amplitude of first harmonic aerodynamic force, low-speed separation and aerodynamic work density. In addition, the relative distribution of the excitation field and the positive work zone also has a direct effect on the suppression of flutter.

The Equilibrium Time and Salt Expansion Characteristic of Sulfate Saline Soil upon Cooling

The salt expansion disease is severe for the soil containing sodium sulfate in cold regions. This paper carried out one-dimensional salt expansion tests of saline soil, the crystallization test of saturated sodium sulfate solution, and the numerical cooling tests to explore the stability time of the salt expansion test and determine the standard procedure of salt expansion tests. The test results demonstrate that (i) the temperature equilibrium and the crystallization process are almost simultaneously completed in both sulfate saline soil and sulfate solution upon cooling; (ii) referring to the deformation equilibrium standard used in soil consolidation test, an expansion rate of less than 0.02 mm/h is suggested in the saline expansion test; and (iii) the equilibrium time is found to have a quadratic polynomial relationship to sample size and is much shorter under liquid bath conditions than under gas bath conditions. Based on these findings, a standard procedure of the one-dimensional salt expansion test is proposed, in which the test equipment, the test process, the deformation stabilization time of salt expansion, and the data processing method are provided. As the deformation and the temperature are synchronized, the deformation stabilization time of samples with different sizes in different cooling media is recommended.

Resistance to the alkali-aggregate reaction of sustainable mortars produced with scheelite tailings in replacing natural sand aggregates

This work produced coating mortars with scheelite tailings (ST) in total replacement of natural sand aggregate. The chemical and mineralogical composition of the scheelite tailings was determined by X-ray diffraction (XRD) and X-ray fluorescence (XRF). Mortar samples with a mass proportion of 1:2:9 (cement: lime: sand/scheelite tailings) were prepared with and without the scheelite tailings. The mortars were evaluated by mercury intrusion porosimetry and compressive and flexural strength tests. The resistance to the alkali-aggregate reaction was assessed from the bar expansion test and by scanning electron microscopy (SEM) in the crack and pore regions. The results indicate that until the 22nd day, the scheelite tailings were not reactive; however, in 28 days, the expansion was deleterious. SEM images did not detect the presence of amorphous alkaline gel characteristic of the alkali-aggregate reaction. Therefore, although the mortar with scheelite tailings aggregate has shown the deleterious potential to 28 days, mechanical tests indicate that it has the potential to be used as a coating mortar.

Microstructure analysis and crack nucleation in TWIP steel tube at expansive deformation

The expansion test of twinning induced plastic (TWIP) steel tube was carried out at room temperature. Cracks appeared inside the tube edge when TWIP steel tube expands by 15.6%. The microstructure evolution, deformation mechanism and crack generation of TWIP steel after expansion were investigated by XDR OM TEM and EBSD. The results show that TWIP steel tube still austenite phase after expansion at room temperature; a great deal of dislocations are gathered around the grain boundaries and twin boundaries, the integral number of twins is high, and the mechanism of expansion deformation is the joint action of dislocations slip and deformation twins; Twins produce a large number of finer secondary or even multiple twins, intersecting each other; After expansion, the silk texture with direction of <111>∥X0 dominated by rotating brass texture {110}<111> is gradually produced through grain deformation and rotation; The proportion of small angle grain boundaries increased greatly; It is deduced that the criterion of crack nucleation is based on the difference between the dislocation pile-up energy (DPE) and the crack nucleation energy (CNE), and the expansion deformation process of TWIP steel satisfies the condition of crack nucleation.

Preparation and Evaluation of Ammonium Adipate Solutions as Inhibitors of Shale Rock Swelling

This study aimed to evaluate the inhibitory effect of a series of ammonium adipate solutions (AASs) by using the linear expansion test, thermogravimetric analysis (TGA), and particle size distribution analysis, and to examine the underlying inhibitory mechanism. A series of AASs was prepared from adipic acid and amines as small-molecule inhibitors of oil shale rock swelling. They were then evaluated by the bentonite linear expansion test. The best one, namely, AAS-8 (synthesized with adipic acid and tetraethylenepentamine in a ratio of acid group to amine group of 1:2), was evaluated in a water-based drilling fluid. The linear expansion test showed that the linear expansion rate of AAS-8 was the lowest (59.61%) when the concentration was 0.1%. The evaluation of the drilling fluid revealed that AAS-8 had a strong inhibitory effect on the swelling of hydrated bentonite particles in the water-based drilling fluid and was compatible with carboxymethyl cellulose (CMC) and modified starch. The inhibition mechanism of AAS-8 was investigated using TGA and particle size distribution analysis, which demonstrated that AAS-8 might enter the clay layer and bind the clay sheets together by electrostatic adsorption and hydrogen bonding.