A Rotating Laser-Doppler Anemometry System for Unsteady Relative Flow Measurements in Model Centrifugal Impellers

1994 ◽  
Vol 116 (2) ◽  
pp. 260-268 ◽  
Author(s):  
M. Abramian ◽  
J. H. G. Howard
Keyword(s):  
Laser Doppler Anemometry ◽  
Fluid Dynamic ◽  
Rotating Stall ◽  
Secondary Flows ◽  
Operating Conditions ◽  
Laser Doppler ◽  
Low Flow ◽  
Centrifugal Impeller ◽  
Flow Measurements ◽  
Relative Flow

The behavior of the relative flow in centrifugal turbomachines is extremely complex due to the existence of various fluid dynamic phenomena and their interaction. At design and off-design operating conditions, the relative flow is subject to stationary unsteadiness, which includes the flow separation and wakes associated with passage pressure gradients, secondary flows, and boundary layer stability. It is also subject to periodic unsteadiness from the rotating stall and the cyclic flow phenomena induced by the casing. This paper describes the mechanical and optical design of a rotating laser-Doppler anemometry system, which allows direct measurement of the relative flow by means of an optical derotator. By isolating the impeller rotational frequency from the sampling frequency, it allows direct time-averaged measurements of the stationary behavior of the relative flow along with the ensemble (phase)-averaged measurements of its periodic behavior. Its success is demonstrated with measurements conducted in a low specific speed centrifugal impeller fitted with a single volute. Sample results of the time-averaged blade-to-blade variation of total relative velocities along with their associated turbulence intensities are reported. The (periodic) cyclic variations of the impeller exit flow, induced by the volute at low flow rates, are also presented for the suction and pressure sides.

scholarly journals A Rotating Laser-Doppler Anemometry System for Unsteady Relative Flow Measurements in Model Centrifugal Impellers

1993 ◽  
Author(s):  
M. Abramian ◽  
J. H. G. Howard
Keyword(s):  
Laser Doppler Anemometry ◽  
Fluid Dynamic ◽  
Rotating Stall ◽  
Secondary Flows ◽  
Operating Conditions ◽  
Laser Doppler ◽  
Low Flow ◽  
Centrifugal Impeller ◽  
Flow Measurements ◽  
Relative Flow

The behaviour of the relative flow in centrifugal turbomachines is extremely complex due to the existence of various fluid dynamic phenomena and their interaction. At design and off-design operating conditions, the relative flow is subject to stationary unsteadiness which includes the flow separation and wakes associated with passage pressure gradients, secondary flows, and boundary layer stability. It is also subject to periodic unsteadiness from the rotating stall and the cyclic flow phenomena induced by the casing. This paper describes the mechanical and optical design of a rotating laser-Doppler anemometry system which allows direct measurement of the relative flow by means of an optical de-rotator. By isolating the impeller rotational frequency from the sampling frequency, it allows direct time-average measurements of the stationary behaviour of the relative flow along with the ensemble (phase)-average measurements of its periodic behaviour. Its success is demonstrated with measurements conducted in a low specific speed centrifugal impeller fitted with a single volute. Sample results of the time-averaged blade-to-blade variation of total relative velocities along with their associated turbulence intensities are reported. The (periodic) cyclic variations of the impeller exit flow, induced by the volute at low flow rates, are also presented for the suction and pressure sides.

Experimental Investigation of the Steady and Unsteady Relative Flow in a Model Centrifugal Impeller Passage

1994 ◽  
Vol 116 (2) ◽  
pp. 269-279 ◽  
Author(s):  
M. Abramian ◽  
J. H. G. Howard
Keyword(s):  
Laser Doppler Anemometry ◽  
Fluid Dynamic ◽  
Rotating Stall ◽  
Secondary Flows ◽  
Operating Conditions ◽  
Low Flow ◽  
Centrifugal Impeller ◽  
Low Specific Speed ◽  
Specific Speed ◽  
Relative Flow

The behavior of the relative flow in centrifugal turbomachines is extremely complex due to the existence of various fluid dynamic phenomena and their interaction. At design and off-design operating conditions, the relative flow is subject to stationary unsteadiness, which includes flow separation and wakes associated with passage pressure gradients, secondary flows, and boundary layer stability. It may also be subject to periodic unsteadiness, as are the rotating stall and cyclic flow phenomena induced by the casing. This paper describes detailed measurements of the relative velocity field in a very low specific speed centrifugal pump impeller (Ns = 515). Measurements were conducted by means of a recently developed rotating laser-Doppler anemometry system. Detailed quantitative descriptions of the mean and fluctuating components of the primary and secondary velocity fields are presented for an impeller without volute at design, 50 percent design, and shut-off conditions. The flow pattern in this low specific speed impeller with high blade loading is dominated by the relative eddy (a phenomenon also present in potential flow), which has suppressed suction side separation. The cyclic variation of the impeller exit flow, induced by the volute at low flow rates, is also presented for an impeller fitted with a volute.

scholarly journals Experimental Investigation of the Steady and Unsteady Relative Flow in a Model Centrifugal Impeller Passage

1993 ◽  
Author(s):  
M. Abramian ◽  
J. H. G. Howard
Keyword(s):  
Laser Doppler Anemometry ◽  
Quantitative Description ◽  
Rotating Stall ◽  
Secondary Flows ◽  
Operating Conditions ◽  
Low Flow ◽  
Centrifugal Impeller ◽  
Low Specific Speed ◽  
Specific Speed ◽  
Relative Flow

The behaviour of the relative flow in centrifugal turbomachines is extremely complex due to the existence of various fluid dynamic phenomena and their interaction. At design and off-design operating conditions, the relative flow is subject to stationary unsteadiness which includes flow separation and wakes associated with passage pressure gradients, secondary flows, and boundary layer stability. It may also be subject to periodic unsteadiness such as is the rotating stall and cyclic flow phenomena induced by the casing. This paper describes detailed measurements of the relative velocity field in a very low specific speed centrifugal pump impeller (Ns=515). Measurements were conducted by means of a recently developed rotating laser-Doppler anemometry system. Detailed quantitative description of the mean and fluctuating components of the primary and secondary velocity fields are presented for an impeller without volute at design, 50% design and shut-off conditions. The flow pattern in this low specific speed impeller with high blade loading is dominated by the relative eddy (a phenomenon also present in potential flow) which has suppressed suction side separation. When the impeller was fitted with a volute, the cyclic variation of the impeller exit flow, induced by the volute at low flow rates, is also presented.

Effects of Seal Geometry on Dynamic Impeller Fluid Forces and Moments

2003 ◽  
Vol 125 (5) ◽  
pp. 786-795 ◽  
Author(s):  
Yoshiki Yoshida ◽  
Yoshinobu Tsujimoto ◽  
Goh Morimoto ◽  
Hiroki Nishida ◽  
Shigeki Morii
Keyword(s):  
Force Sensor ◽  
Rotating Stall ◽  
Low Flow ◽  
Centrifugal Impeller ◽  
Face Seal ◽  
Vaneless Diffuser ◽  
Fluid Force ◽  
Fluid Forces ◽  
Whirling Motion ◽  
Force Moment

This paper reports an experimental investigation of the rotordynamic fluid force and moment on a centrifugal impeller with three types of wear-ring seals; i.e., a face seal and two types of toothed seals. The impeller is equipped with a vaneless diffuser. Rotordynamic fluid forces and moments on the impeller in whirling motion were measured directly by using four-axis force sensor. Unsteady pressures were measured at several locations in the diffuser. It was found that, (1) at low flow rate, the fluid force and fluid force moment become maximum at a certain whirling speed caused by a coupling between the whirl motion and vaneless diffuser rotating stall and (2) the seal geometry with axial seal affects the direction of the coupled fluid force relative to the direction of eccentricity through the change in the unsteady leakage flow due to the whirl.

scholarly journals A spectral analysis of laser Doppler anemometry turbulent flow measurements in a ship air wake

2015 ◽  
Vol 229 (12) ◽  
pp. 2309-2320 ◽  
Author(s):  
R Bardera-Mora ◽  
MA Barcala-Montejano ◽  
A Rodríguez-Sevillano ◽  
G González de Diego ◽  
M Ruiz de Sotto
Keyword(s):  
Spectral Analysis ◽  
Turbulent Flow ◽  
Laser Doppler Anemometry ◽  
Laser Doppler ◽  
Flow Measurements

Jet, Wake and Intrinsic Motion in Impellers of Centrifugal Compressors

1996 ◽  
Author(s):  
Y. N. Chen ◽  
U. Seidel ◽  
U. Haupt ◽  
M. Rautenberg
Keyword(s):  
Reverse Flow ◽  
Vortex Pair ◽  
Leading Edge ◽  
Rotating Stall ◽  
Secondary Flows ◽  
Low Flow ◽  
Experimental Result ◽  
Vaned Diffuser ◽  
Measured Velocity ◽  
Intrinsic Motion

It was shown in a previous paper of the authors (1991) that jet and wake in the flow of the impeller of the centrifugal compressor are developed from the Dean’s type vortex pair formed in the curvature of the blade channel. The jet rotating against the sense of the impeller is weakened, and the wake rotating in the sense of the impeller is enhanced during travelling with the flow toward the outlet. This property is attributed to the conservation of the potential vorticity of the vortex. The experimental result obtained by Krain (1984) has confirmed this theory. The secondary flows found by Farge and Johnson (1990) enable the determination of the vorticity of the wake at the outlet of the impeller. It amounts to 6.9 Ω and 5.8 Ω for the radial-blading and the 60°-backswept blading impeller, respectively. The intensity of the vortex jet is weakened to undetectable value for both the impellers. The patterns of these secondary flow fields are also quite different between these two kinds of impellers. Whilst that of the former is controlled by the intrinsic motion, that of the latter is governed by the relative velocity along the blades. Furthermore, the experimental result obtained by the injection of colored dye at the impeller outlet and the measured velocity field around the impeller reveal an intense reverse flow in the radial blading impeller, travelling from the outlet toward the inlet, along the shroud. It can be shown that this reverse flow is caused by the intrinsic motion occuring in this impeller and impinging on the leading edge of the diffuser vane. As the rotating stall is introduced by the reverse flow, the low-solidity vaned diffuser, and still better the vaneless diffuser can therefore shift the stall line to a very low flow rate.

A Study of the Behaviour of Flow in a Diagonal-Flow Turbomachine

1996 ◽  
Author(s):  
Arjun Sarathi Ray
Keyword(s):  
Fluid Dynamic ◽  
Characteristic Curve ◽  
Axial Flow ◽  
Time History ◽  
Rotating Stall ◽  
Flow Coefficient ◽  
Flow Measurements ◽  
Flow Rates ◽  
Rotor Losses ◽  
Reduced Flow

Experiments were conducted on a diagonal-flow machine to study the behaviour of flow. Measurements showed that at reduced flow rates, reversal of flow occurs near the tip upstream of the rotor and near the hub downstream. At high flow rates, the flow reverses near tip at downstream only. In fact, there is only a limited regime of operation where the flow is not reversed before or after the impeller. The best fluid-dynamic efficiency was observed to be midway of this non-reversed flow regime. Through-flow solutions of the mean hub-to-tip streamsurface were carried out by streamline curvature computation and compared with experimental results. The comparison showed good agreement of the predicted values with the experimental data. However, attempts to compare theoretical estimates of rotor losses with experimental measurements showed that the existing loss models are inadequate for loss prediction and further work is required in this direction. The head-flow characteristic of the machine showed a droop at reduced flow rates, typical of what one usually notices in an axial-flow machine with the onset of blade stall. Study of the time history of velocity downstream of rotor illustrated that unlike rotating ‘stall-cells’ in axial-flow machines, the blade stall in the present case did not possess any regular pattern nor any unique speed of propagation. Near the hub at downstream of rotor, where the flow finally reverses upon reduction of flow rate, the stall appeared as patches of ‘blockage’ type disturbance over an otherwise systematic train of blade wakes when the flow coefficient reaches a value where the droop in the characteristic curve starts.

Turbulent Flow Measurements by Laser-Doppler Anemometry in Motored Piston-Cylinder Assemblies

1979 ◽  
Vol 101 (2) ◽  
pp. 208-216 ◽  
Author(s):  
A. P. Morse ◽  
J. H. Whitelaw ◽  
M. Yianneskis
Keyword(s):  
Cylinder Head ◽  
Laser Doppler Anemometry ◽  
Laser Doppler ◽  
Cylinder Wall ◽  
Mean Velocity ◽  
Flow Measurements ◽  
Piston Bowl ◽  
Piston Cylinder ◽  
Large Vortex ◽  
Strong Vortex

Laser-Doppler anemometry has been used to quantify the mean velocity and turbulence characteristics of the isothermal, incompressible flow within a piston-cylinder arrangement motored without compression at 200 rpm and with idealized inlet geometries corresponding to a pipe and to an annular port located in the centre of the cylinder head. The results indicate that the pipe entry gives rise to a strong vortex near the piston as the indrawn air is deflected radially along the piston face and cylinder wall; this, in turn, gives rise to a weaker, counter-rotating vortex near the cylinder head which grows appreciably as the piston approaches bottom-dead-centre. With the annular-port entry, the inlet jet is angled and results in a flow pattern with a large vortex occupying nearly all of the flow space with much smaller vortices at the corners between the wall and the piston and cylinder heads. The effect of a piston bowl was also investigated for the port entry and is shown to be small.

Sign in / Sign up

Export Citation Format

Share Document