Explore chapters and articles related to this topic
Fatigue
Published in Mark W. Wiggins, Introduction to Human Factors for Organisational Psychologists, 2022
From an operational perspective, the impact of fatigue was illustrated in the crash of Colgan Air Flight 3407, a Bombardier Q400, on February 12, 2009. The aircraft was on descent to Buffalo, New York, having departed Newark, New Jersey. Light snow and fog resulted in ice forming on the leading edge of the wings, increasing drag, and causing a reduction in the airspeed of the aircraft to a point where the stall warning activated. In responding to an impending stall, pilots are taught to lower the attitude of the aircraft and then to increase power. However, in the case of the Flight 3407, the captain pulled back on the yoke, and subsequently applied power, The result was a further ‘pitch-up’ of the aircraft, further restricting the margin for recovery (NSTB, 2010).
Flying Wings (or Tailless Airplanes)
Published in James DeLaurier, Aircraft Design Concepts, 2022
In this case, the wings are swept forward, which offers certain aerodynamic advantages, such as suppression of tip stall. This sophisticated design achieves a remarkable maximum lift/drag ratio of 45:1. A new version of this, the Pioneer 4 with a laminar airfoil, promises to significantly exceed this value.
Pump and fan controls
Published in Raymond F. Gardner, Introduction to Plant Automation and Controls, 2020
Figure 8.12 shows the progression of system curves as a discharge damper closes while modulating flow. As the damper closes, the system resistance increases, the fan rides back on the curve decreasing flow and increasing developed pressure, as would be expected (Figure 8.12b). Eventually, the damper closes enough to put the fan into the unstable operating range, where the fan pressure drops as the damper closes, instead of increasing (Figure 8.12c). At low discharge pressure, the fan curve has two possible operating flowrates, as shown as Q1 and Q2 in Figure 8.11, at which point the fan will surge. Surging occurs as the flow separates from the impeller vane in a condition known as stall. The flow separation and stall occurs when the angle of attack of the relative air flow over the vane exceeds the critical angle of attack. Stall can lead to surging, noise, vibration, fatigue, inefficiency, difficult pressure/flow measurement, and poor system behavior. Instability and surge are a low flow phenomenon and even small amounts would be intolerable in systems requiring fine control, such as combustion-air fans.
Design, electromechanical simulation, and control of a variable speed stall-regulated PMSG-based wind turbine
Published in International Journal of Green Energy, 2019
Ebrahim Mohammadi, Roohollah Fadaeinedjad, Hamid Reza Naji
The main control issues in WTs are associated with the extraction of the maximum power in Region 2 and limitation of the captured power around the rated power in Region 3. Generally, the electrical controllers are used to track the MPP, whereas the mechanical control strategies including pitch, yaw, active stall, and furl controls are used to limit the rotation speed and output power. In the present paper, the generator speed is controlled based on the wind speed-rotor speed curve, obtained in the blade design step, to maximize the captured power in Region 2 and to limit the output power in Region 3 by forcing the blades to operate in the stall mode. Stall is an aerodynamic phenomenon which is happened when the angle of attack exceeds a certain value in high wind speeds. When the blades operate in the stall region, the lift forces on the blades are reduced; hence, the mechanical torque and captured power are limited. The generator-connected converter is utilized to control the rotor rotation speed based on the wind speed – rotor speed curve. The network-connected converter is used to regulate the DC link voltage and to keep the system at unity power factor.
Hydrodynamic design of a horizontal axis current turbine with passive flow control using vortex generator and inserted tube
Published in International Journal of Green Energy, 2023
Among various possible options to increase the total extracted power from a current turbine, the performance improvement of the blade foil has been considered in this work. Specifically, increasing the lift force coefficients at various angles of attack and delaying the undesirable stall appearance have been targeted by adopting flow control techniques. As suggested by various researchers, this can be achieved through several approaches, such as synthetic jet actuators (Cattafesta and Sheplak 2011), moving object or surface actuators (Cattafesta and Sheplak 2011), plasma actuators (Cattafesta and Sheplak 2011), pulsed combustion actuators (Cattafesta and Sheplak 2011), fluidic actuators (Cattafesta and Sheplak 2011), vortex generators (Manolesos and Voutsinas 2015), rigid flaps (Li et al. 2013), dimples (Beves and Barber 2011), slots (Weick and Wenzinger 1933), etc. Unlike the active flow separation control methods, the passive flow control techniques do not require external energy into the system, i.e., such methods are primarily based on bringing high kinetic energy fluid from the free stream to the area of low kinetic energy fluid which is on the verge of separation. Application of such systems is often a lot easier since aspects like size, additional weight, initial cost, failure risk, and maintenance cost are significantly less compared to active devices. Thus, passive techniques like vortex generators have gained considerable popularity in the aircraft industry. A details discussion on various passive flow control methods has been discussed in (Belamadi et al. 2016; Kundu 2019, 2020a, 2020b; Kundu, Sarkar, and Nagarajan 2019, 2020; Lin 1999).
Machine Learning to Predict Aerodynamic Stall
Published in International Journal of Computational Fluid Dynamics, 2022
Ettore Saetta, Renato Tognaccini, Gianluca Iaccarino
Airfoil stall is a strongly non-linear phenomenon corresponding to the loss of lift force and a primary design consideration for airplanes and rotor-crafts. Figure 1 illustrates the lift curves (variation of lift coefficient as function of the angle of attack α) for the Boeing VR12 airfoil in steady Figure 1(a) and unsteady Figure 1(b) regimes, experiment by Matalanis et al. (2016). The figure also shows the capabilities of CFD simulations as obtained by present authors (SU2 RANS and URANS solver (Economon et al. 2016)) and by Matalanis et al. (CFL3D) in predicting these phenomena.