Investigation of the formation and evolution of over-tip shock waves in the pressure-driven tip leakage flow by time-resolved schlieren visualization

Time-resolved schlieren visualization and transonic wind tunnel are used to investigate tip leakage flows (TLFs) over several generic blade tip models. Focus is on the generation and evolution of the over-tip shock waves in the clearance region. A multi-cutoff superposition technique is developed to improve the schlieren system for better visualization. Unsteady flow structures, such as over-tip shock oscillation, shear-layer flapping, and vortex shedding, are revealed by Fourier analysis and dynamic mode decomposition. To predict the generation and decaying of over-tip shocks, a simplified model is proposed by analogizing the shock system to be an N-shaped sawtooth wave. The results show that (1) the proposed model is able to capture the main features of the generation and decaying of over-tip shock waves. The processes of shock generation, decaying, and fading-out are dominated by the mean background flow, the shock state, and the flow fluctuations, respectively. Adding extra coming flow fluctuations can be an efficient way to control the evolution of over-tip shock system. (2) The shock-oscillating frequency is kept the same with the shear-layer flapping, and shock waves with a given oscillating frequency range is constrained to a specific position range. This is termed the “lock-in effect,” which is also observed in TLFs over contoured blade tips. The non-uniformity generation and the nonlinear propagation of shock waves are responsible for this effect. Constrained by this effect, the evolution of over-tip shock waves is separated into four discrete phases. Thus, this effect can be applied for the control of TLFs

The Effect of Aminolevulinic Acid on Physiological and Biochemical Characters of Red-fleshed Apple (Malus sp. Genotype R1R1) under Salinity Stress

The present study was conducted to evaluate the ameliorating effect of 5-aminolevulinic acid (ALA) on physiological and biochemical changes of induced NaCl-salinity stress on in vitro shoot and callus cultured of red-fleshed apple. Shoot and callus segments of the red-flesh apple of Local Iranian genotype were cultured on MS medium containing different levels of NaCl (0, 30, 60 and 90 mM) and ALA (0, 2.5, 5, 10 and 20 µM). Physiological and biochemical variations of treated explants with or without NaCl and ALA treatments were recorded. In both explants, salinity reduced chlorophyll and carotenoids contents, but the activities of antioxidant enzymes and accumulation of total phenol and anthocyanin increased with increasing salinity level (90mM). Exogenous ALA in 5 and particularly in 10 µM was effective in enhancing chlorophyll and carotenoids contents, increasing the activities of superoxide dismutase, ascorbate peroxidase and accumulating of total phenol and anthocyanin. These results indicate that ALA has a powerful salinity-ameliorating potential on in vitro cultured shoot and callus of Iranian red-fleshed apple