Dynamic stall due to a ramp-type pitching motion is investigated on the NACA 0012 airfoil at chord Reynolds number of $Re_{c}=1.0\times 10^{6}$ through use wall-resolved large-eddy simulation. Emphasis placed unsteady boundary-layer interactions that develop as approaches stall. At this it shown turbulent separation moves upstream across much suction surface. When reaches leading-edge bubble, bursting event initiated leading strong coherent vortex structure. This wraps up shear layer form...

Dynamic stall represents a challenge in number of engineering applications including rotorcraft, maneuvering aircraft, gust encounters, and wind turbines. Delay the onset dynamic mitigation its undesirable transient loading effects have been sought past five decades employing passive active flow control techniques. Development improved approaches requires detailed characterization underlying boundary-layer processes preceding abrupt unsteady separation. Such information is difficult to...

Efforts to increase individual blade loading in the low pressure turbine have resulted geometries optimized for midspan performance. Many researchers shown that increased and a front-loaded distribution each separately contribute losses endwall region. A detailed investigation of baseline flow L2F profile, which is high-lift front loaded performed. In-plane velocity vectors total loss maps are obtained five planes oriented normal surface three Reynolds numbers. row pitched skewed jets...

The perturbation dynamics over an airfoil laminar separation bubble (LSB) is examined via resolvent analysis. computational burden of singular value decomposition (SVD) relieved through the randomized method, and local energy amplification mechanisms LSB are extracted from global operator with discounting approach. With applications input output windows, it shown that Kelvin-Helmholtz instability dominates LSB, optimal momentum-based forcing aligns tangential direction surface.

Recent applications of active flow control to the low-pressure turbine section a gas are reviewed and evaluated. Unique aspects environment such as freestream turbulence, secondary flows, unsteady wakes create challenges for that must be considered during design implementation. Applications four different mechanisms two challenging phenomena (separation flows) described in detail. Although significant work is yet required before viable implementation can fielded, several show considerable promise.

Large-eddy simulations of the onset dynamic stall for a NACA 0012 airfoil, pitching at constant rate, are performed chord Reynolds number . Using four simulations, spanning , effects compressibility examined number. The interplay between laminar separation bubble (LSB), within turbulent boundary layer, and is elucidated. It shown that increased results in earlier dynamic-stall related to bursting leading-edge LSB. Because this onset, which occurs leading edge, role boundary-layer diminished....

Efforts to reduce blade count and avoid boundary layer separation have led low-pressure turbine airfoils with significant increases in loading as well front-loaded pressure distributions. These features been independently shown increase losses within the secondary flow field at end wall. Compound angle blowing from discrete jets on suction surface near wall has be effective reducing these increased enabling efficient use of highly loaded designs. In this study, experiments are performed...

The physics of control by pulsed blowing on a NACA natural laminar flow airfoil is studied using hot-film anemometry. Measurements in the uncontrolled separated shear layer indicate that vortex shedding taking place due to Kelvin–Helmholtz-type inviscid instability. Steady and external acoustic excitation used as well decouple frequency content perturbation from vorticity introduced jet. Acoustic introduces either most unstable or harmonics carrier range, which amplify exponentially...

A recently proposed high-frequency control concept for dynamic-stall mitigation is demonstrated using large-eddy simulation of a pitching NACA 0012 airfoil at chord Reynolds number . At this condition, dynamic stall occurs when the suction-surface laminar separation bubble (LSB) breaks down due to interaction with turbulent as it propagates upstream. It shown that forcing introduced near leading edge, targeting most amplified frequency LSB, LSB amplifies disturbances, resulting in more...

The performance of active flow control on a NACA laminar airfoil at poststall angle attack 20 deg is evaluated using discrete, wall-normal pulsed jets. chord Reynolds number 64,000, and actuation implemented near the leading edge airfoil. For periods equal to one convective period two periods, average lift coefficient increases monotonically as duty cycle reduced, for given blowing ratio. Flow reattachment achieved following termination short duration pulse, point propagates toward trailing...

The flow of interest is a streamwise vortex interacting with wall. This proposed as simplified model generic secondary stemming from blade side-wall junction such those at the wing-body an aircraft or blade-hub compressor turbine airfoil. current computational campaign has shown that Crowtype and Widnall-type instabilities do exist between wall in similar manner pair. results modal analysis also provide shape adjoint mode corresponding to Crow Widnall instabilities. These are related their...

Very-low-amplitude, high-frequency forcing is used to manipulate the laminar separation bubble on a NACA 0012 airfoil pitching at constant rate. Properly tuning frequency track changing Kelvin-Helmholtz instability results in significant delay of onset dynamic stall.

A large-amplitude low-frequency oscillation has been reported in the literature for some airfoils a small range of angles attack before stall. In current study, same oscillations are shown to be triggered by two methods active flow control at poststall angles. Active is applied form external acoustic excitation or row discrete jets that operated pulsed steady mode. Conditionally averaged particle image velocimetry and time-resolved surface pressure measurements used evaluate spatial temporal...

This paper summarizes findings from the 6th AIAA Propulsion Aerodynamics Workshop (PAW) nozzle test case. The focus of workshop was turbulent supersonic round jets with variation in jet Mach number and heating. Three nozzles were examined having on-design numbers 1.36, 1.63, 2.00. Five cases examined: A heated for each these three at conditions, a temperature matched condition an off-design 1.63 nozzle. Computational fluid dynamics (CFD) solutions compared non-intrusive measurements plume...

A new high-speed linear cascade has been developed for low-pressure turbine (LPT) studies at The Ohio State University. compressible LPT profile is tested in the facility and its baseline performance different operating conditions assessed by means of isentropic Mach number distribution wake total pressure losses. Active flow control implemented through a spanwise row vortex-generator jets (VGJs) located 60% chord on suction surface. purpose study to document effectiveness VGJ flow. effect...

The mechanism of separation control by sound excitation is investigated on the aft-loaded low-pressure turbine (LPT) blade profile, L1A, which experiences a large boundary layer at low Reynolds numbers. Previous work authors has shown that laminar bubble such as experienced front-loaded L2F its best performance most unstable frequency shear due to exploitation linear instability mechanism. different loading distribution L1A increases distance separated from wall and same no longer effective...

The effects of inlet endwall boundary layer thickness and up-stream unsteady wakes are investigated experimentally in a low-speed linear cascade. examined airfoil is the front-loaded L2F, high-lift low-pressure turbine profile with high resistance to separation even low Reynolds number regime. Cases documented without incoming for two layers different at Re = 30,000. Periodic simulated moving bars upstream conditioned two-part splitter plate, one part downstream wake generator. By...