The current paper reports on a new theory developed by modifying the basic Moore-Greitzer model, which can predict the performance of a compression system during the instabilities in more details. The general assumptions such as the compression system layout, the lags in the entrance and exit ducts, the compressor axisymmetric characteristic and the small disturbances are similar to those of Moore-Gereitzer model. However, a second order hysteresis is used in the current work for the pressure rise of the rotor and stator rows. As a result, some new parameters are added to the governing equations, such as the stall cell acceleration ( ), second derivative of the mean axial flow coefficient ( ), second derivative of the disturbance amplitude ( ) and slope of the compressor characteristic curve. This gives the modified model new capabilities, like investigating the transient speed of the stall cell or the effect of the throttling rate on the instabilities, which are discussed in details in the current paper.

In order to upsurge the maneuverability of micro aerial vehicles, a tubercle leading edge inspired by the whale flipper was applied as a passive stall control method. Although this method could be useful to control stall phenomena, the effect of geometrical properties on the flow physic should be investigated to reach the root of them. According to preceding research, the effect of some parameters on the tubercle leading edge wing is a hot topic among researchers. The aim of this research is to explore the effects of sectional wing geometries like amplitude, wavelength, thickness, maximum thickness location, and camber on the aerodynamic feature of full-span tubercle leading edge wing, particularly at 22 degree in Post-stall circumstances. The results present that by reducing the amplitude about 2. 5%c, the lift coefficient upsurges by about 3. 5%, instead, the drag coefficient reduces about 6%. On the other hand, by decreasing the wavelength from 46. 2%c to 11. 7%c, the drag coefficient and the lift coefficient decrease by about 15% and 19%, respectively. Furthermore, as the thickness rises from 10. 55%c to 18. 14%c, the lift and drag coefficient goes down about 9. 4% and 2. 9%, respectively. Furthermore, by increasing the camber from 2. 56%c to 3. 34%c, the lift to drag ratio goes down by about 1. 06%. Finally, by raising the last design variable (maximum thickness location) from 0. 26c to 0. 51c, the lift to drag ratio increases about 13. 7%.

The present research investigates the torsional aeroelasticity of the blade of an H-type vertical axis wind turbine subject to stall and Post-stall conditions in various Reynolds regimes, which is experienced by the blade in a full revolution. In order to simulate the aerodynamics, a new model based on a combination of the Double Multi Streamtubes (DMST) model and the nonlinear multi-criteria Cl- equations, which is depended on the local Reynolds number of the flow, has been proposed. The results indicate that using of multi-criteria function dependent on the Reynolds number for the Cl- curve has improved the prediction of the torsional behavior of the blade in azimuthal rotation of the blade compared to using single-criterion functions and linear aerodynamics. The blade’ s aeroelastic torsion has been studied for various TSR values.

The unstable flow with rotating-stall-like (RS) effects in a rotor-cascade of an axial compressor was numerically investigated. The RS was captured with the reduction in mass flow rate and increasing of exit static pressure with respect to design operating condition of the single rotor. The oscillatory velocity traces during the stall propagation showed that the RS vortices repeat periodically, and the mass flow rate was highly affected by the blockage areas made by stall vortices. The results also showed that large scale vortices highly affects on the generation and growth of the new vortices. An unsteady two-dimensional finite-volume solver was employed for the numerical study which was developed based on Van Leer’s flux splitting algorithm in conjunction with TVD limiters and the κ-ε turbulence model was also employed. The good agreement of the computed mass flow rate with the experimental results validates the numerical study.