The Use of Holographic Interferometry for Turbomachinery Fan Evaluation During Rotating Tests

1988 ◽  
Vol 110 (3) ◽  
pp. 393-400 ◽  
Author(s):  
R. J. Parker ◽  
D. G. Jones
Keyword(s):  
Boundary Layer ◽  
Transonic Flow ◽  
Three Dimensional ◽  
Flow Region ◽  
Vibration Modes ◽  
Design Intent ◽  
Tip Leakage ◽  
Fan Behavior ◽  
Boundary Layer Interaction ◽  
Flow Features

Holography has been developed by Rolls-Royce as a technique for routine use in the evaluation of fan designs for aeroengines. It is used to investigate both aerodynamic and mechanical behavior of the rotating fan. Holographic flow visualization provides clear, three-dimensional images of the transonic flow region between the fan blades. Flow features such as shocks, shock/boundary layer interaction, and over-tip leakage vortices can be observed and measured. Holograms taken through an optical derotator allow vibration modes of the rotating fan to be mapped during resonance or flutter. Examples are given of the use of both techniques at rotational speeds up to and in excess of 10,000 rpm. Holography has provided valuable information used to verify and improve numerical modeling of the fan behavior and has been successful in evaluating the achievement of design intent.

Aerodynamics of Boundary Layer Ingesting Fans

2014 ◽  
Author(s):  
E. J. Gunn ◽  
C. A. Hall
Keyword(s):  
Boundary Layer ◽  
Three Dimensional ◽  
Low Speed ◽  
Turbofan Engines ◽  
Unsteady Separation ◽  
Fuel Burn ◽  
Boundary Layer Interaction ◽  
Flow Features ◽  
Structure Strength ◽  
Transonic Fan

Boundary Layer Ingesting (BLI) turbofan engines could offer reduced fuel burn compared with podded engines, but the fan stage must be designed to run continuously with severe inlet distortion. This paper aims to explain the fluid dynamics and loss sources in BLI fans running at a cruise condition. High-resolution experimental measurements and full-annulus unsteady CFD have been performed on a low-speed fan rig running with a representative BLI inlet velocity profile. A three-dimensional flow redistribution is observed, leading to an attenuation of the axial velocity non-uniformity upstream of the rotor and to non-uniform swirl and radial angle distributions at rotor inlet. The distorted flow field is shown to create circumferential and radial variations in diffusion factor with a corresponding loss variation around the annulus. Additional loss is generated by an unsteady separation of the casing boundary layer, caused by a localised peak in loading at the rotor tip. Non-uniform swirl and radial angles at rotor exit lead to increased loss in the stator due to the variations in profile loss and corner separation size. An additional CFD calculation of a transonic fan running with the same inlet profile is used to show that BLI leads to wide variations in rotor shock structure, strength and position and hence to loss generation through shock-boundary layer interaction, but otherwise contained the same flow features as the low-speed case. For both fan geometries, BLI was found to reduce the stage efficiency by around 1–2% relative to operation with uniform inlet flow.

Turbulence structure of a reattaching mixing layer

1981 ◽  
Vol 110 ◽  
pp. 171-194 ◽  
Author(s):  
C. Chandrsuda ◽  
P. Bradshaw
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Reynolds Shear Stress ◽  
Mixing Layer ◽  
Three Dimensional ◽  
Flow Region ◽  
Turbulent Energy ◽  
Turbulence Structure ◽  
Hot Wire ◽  
Recirculating Flow

Hot-wire measurements of second- and third-order mean products of velocity fluctuations have been made in the flow behind a backward-facing step with a thin, laminar boundary layer at the top of the step. Measurements extend to a distance of about 12 step heights downstream of the step, and include parts of the recirculating-flow region: approximate limits of validity of hot-wire results are given. The Reynolds number based on step height is about 105, the mixing layer being fully turbulent (fully three-dimensional eddies) well before reattachment, and fairly close to self-preservation in contrast to the results of some previous workers. Rapid changes in turbulence quantities occur in the reattachment region: Reynolds shear stress and triple products decrease spectacularly, mainly because of the confinement of the large eddies by the solid surface. The terms in the turbulent energy and shear stress balances also change rapidly but are still far from the self-preserving boundary-layer state even at the end of the measurement region.

The Behavior of the Casing Boundary Layer With the Presence of Tip Leakage Vortex

2018 ◽  
Author(s):  
Xi Nan ◽  
Feng Lin ◽  
Takehiro Himeno ◽  
Toshinori Watanabe
Keyword(s):  
Boundary Layer ◽  
Skin Friction ◽  
Three Dimensional ◽  
Pressure Rise ◽  
Rotating Stall ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Transonic Compressor ◽  
Flow Loss ◽  
Produce Flow

Casing boundary layer effectively places a limit on the pressure rise capability achievable by the compressor. The separation of the casing boundary layer not only produce flow loss but also closely related to the compressor rotating stall. The motivation of this paper is to present a viewpoint that the casing boundary layer should be paid attention to in parallel with other flow factors on rotating stall trigger. This paper illustrates the casing boundary layer behavior by displaying its separation phenomena with the presence of tip leakage vortex at different flow conditions. Skin friction lines and the corresponding absolute streamlines are used to demonstrate the three-dimensional flow patterns on and near the casing. The results depict a Saddle, a Node and several tufts of skin friction lines dividing the passage into four zones. The tip leakage vortex is enfolded within one of the zones by the separated flows. All the flows in each blade passage are confined within the passage as long as the compressor is stable. The casing boundary layer of a transonic compressor is also examined in the same way, which results in qualitatively similar zonal flows that enfolds the tip leakage vortex. This research develops a new way to study the casing boundary layer in rotating compressors. The results may provide a first-principle based explanation to stalling mechanisms for compressors that are casing sensitive.

Self-Excited Oscillation of Transonic Flow Around an Airfoil in Two-Dimensional Channel

1989 ◽  
Author(s):  
Kazuomi Yamamoto ◽  
Yoshimichi Tanida
Keyword(s):  
Boundary Layer ◽  
Shock Wave ◽  
Transonic Flow ◽  
Stokes Equations ◽  
Flow Region ◽  
Boundary Layer Separation ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Layer Separation ◽  
Excited Oscillation

A self-excited oscillation of transonic flow in a simplified cascade model was investigated experimentally, theoretically and numerically. The measurements of the shock wave and wake motions, and unsteady static pressure field predict a closed loop mechanism, in which the pressure disturbance, that is generated by the oscillation of boundary layer separation, propagates upstream in the main flow and forces the shock wave to oscillate, and then the shock oscillation disturbs the boundary layer separation again. A one-dimensional analysis confirms that the self-excited oscillation occurs in the proposed mechanism. Finally, a numerical simulation of the Navier-Stokes equations reveals the unsteady flow structure of the reversed flow region around the trailing edge, which induces the large flow separation to bring about the anti-phase oscillation.

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