Effects of System Rotation on the Performance of Two-Dimensional Diffusers

1976 ◽  
Vol 98 (3) ◽  
pp. 422-429 ◽  
Author(s):  
P. H. Rothe ◽  
J. P. Johnston
Keyword(s):  
Rotation Number ◽  
Rectangular Cross Section ◽  
Flow Distribution ◽  
Suction Side ◽  
Area Ratio ◽  
Pressure Recovery ◽  
Centrifugal Impeller ◽  
Two Dimensional ◽  
Recovery Coefficient ◽  
Coriolis Acceleration

Experiments with incompressible flow are reported concerning the effects of Coriolis acceleration on flow separation and on separated flow in plane-wall diffusers of rectangular cross section. The diffusers were rotated about an axis perpendicular to the plane of the nearly two-dimensional flow in order to simulate some features of the blade-to-blade flow distribution in the radial portion of the centrifugal impeller. Various stall regimes are mapped on coordinates of rotation number and diffuser area ratio (at fixed wall length). Diffuser pressure-recovery coefficient is reported as a function of area ratio and rotation number. These data demonstrate that, by suppressing turbulent mixing and shear stress in the suction-side boundary layers, the Coriolis acceleration field greatly enhances the tendency for stall to appear in a diffuser. This effect causes a corresponding reduction in the throat-to-exit pressure recovery as compared to that of nonrotating diffusers of the same geometry and inlet flow blockage.

Performance optimization for two-dimensional rectangular diffuser by momentum injection using computational fluid dynamics

2006 ◽  
Vol 220 (12) ◽  
pp. 1775-1783 ◽  
Author(s):  
T Singhal ◽  
S N Singh ◽  
S Mathur ◽  
R K Singh
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Performance Optimization ◽  
Flow Distribution ◽  
Boundary Layer Separation ◽  
Pressure Recovery ◽  
Two Dimensional ◽  
Recovery Coefficient ◽  
Moving Surface ◽  
Pressure Recovery Coefficient

This article explores a non-conventional method for improvement of performance of a wide-angle two-dimensional rectangular diffuser. Computational fluid dynamics investigation has been carried out to analyse the effect of injecting momentum through a moving surface to control the boundary layer separation close to the wall of a two-dimensional rectangular diffuser. A cylinder was placed at the diffuser inlet and rotated at various speeds. It is seen that injection of momentum through the moving surface delays flow separation, thereby increasing the pressure recovery coefficient. An increase in the rotational speed of the cylinder from 1500 to 5500 rad/s improves the pressure recovery coefficient marginally. Placing another cylinder at a preidentified location and rotating both cylinders at the same speed further improves the pressure recovery. Overall improvement in pressure recovery is ∼28 per cent from 0.63 to 0.81. Besides improvement of pressure recovery, the flow distribution in the core region also improves significantly.

Effect of the turning angle on the flow and performance characteristics of long S-shaped circular diffusers

2003 ◽  
Vol 217 (1) ◽  
pp. 29-41 ◽  
Author(s):  
R B Anand ◽  
L Rai ◽  
S N Singh
Keyword(s):  
Total Pressure ◽  
Static Pressure ◽  
Area Ratio ◽  
Secondary Flows ◽  
Performance Characteristics ◽  
Pressure Recovery ◽  
Recovery Coefficient ◽  
Turning Angle ◽  
And Performance ◽  
Pressure Recovery Coefficient

The effect of the turning angle on the flow and performance characteristics of long S-shaped circular diffusers (length-inlet diameter ratio, L/Di = 11:4) having an area ratio of 1.9 and centre-line length of 600 mm has been established. The experiments are carried out for three S-shaped circular diffusers having angles of turn of 15°/15°, 22.5°/22.5° and 30°/30°. Velocity, static pressure and total pressure distributions at different planes along the length of the diffusers are measured using a five-hole impact probe. The turbulence intensity distribution at the same planes is also measured using a normal hot-wire probe. The static pressure recovery coefficients for 15°/15°, 22.5°/22.5° and 30°/30° diffusers are evaluated as 0.45, 0.40 and 0.35 respectively, whereas the ideal static pressure recovery coefficient is 0.72. The low performance is attributed to the generation of secondary flows due to geometrical curvature and additional losses as a result of the high surface roughness (~0.5 mm) of the diffusers. The pressure recovery coefficient of these circular test diffusers is comparatively lower than that of an S-shaped rectangular diffuser of nearly the same area ratio, even with a larger turning angle (90°/90°), i.e. 0.53. The total pressure loss coefficient for all the diffusers is nearly the same and seems to be independent of the angle of turn. The flow distribution is more uniform at the exit for the higher angle of turn diffusers.

Turbulent Flows in a Two-Dimensional 180° -Curved Diffuser With a Guide Vane

2002 ◽  
Author(s):  
Mohamed S. Mohamed
Keyword(s):  
Turbulent Flows ◽  
Guide Vane ◽  
Dynamic Pressure ◽  
Transverse Velocity ◽  
Simple Algorithm ◽  
Pressure Recovery ◽  
Experimental Investigations ◽  
Two Dimensional ◽  
Recovery Coefficient ◽  
Numerical Predictions

Numerical and experimental investigations of the flow in a two-dimensional 180°-curved diffuser, with a guide vane interposed in the diffuser, is presented to clarify their characteristic and to improve the curved diffuser performance. Particular attention is focused on the effect of the variation in the interposed position of the guide vane on the flow field and pressure recovery. Measurements for mean longitudinal and transverse velocity profiles as well as the wall static pressure are performed at different downstream stations. Comparisons are made between the present measurements for the diffuser with a guide vane and without a guide vane [10]. The numerical investigation is based on the solution of the governing equations using a finite volume technique employing SIMPLE algorithm on co-located body-fitted grids. The two-equation model of turbulence, standard k-ε model, and the modified k-ε model [15] are employed in this investigation. The study indicated that the emerging velocity distribution is more uniform than that associated with flow in the diffuser without a guide vane. The presence of a guide vane is shown to suppress the formation of the region of flow separation, as a consequence, the performance of the diffuser is improved. The overall pressure recovery is 54% of the inlet dynamic pressure. The comparison between the numerical and experimental results indicates that the modified k-ε model satisfactorily predicts the overall characteristics of the flow in the diffuser. Numerical predictions show that the best position for a guide vane is positioning the vane towards the convex wall of the diffuser. Diffusers with a guide van at B/W1 = 0.25 to 0.333 give the highest-pressure recovery coefficient.

Improvement of the Performance of Conical Diffusers by Vortex Generators

1974 ◽  
Vol 96 (1) ◽  
pp. 4-10 ◽  
Author(s):  
Y. Senoo ◽  
M. Nishi
Keyword(s):  
Boundary Layer ◽  
Layer Thickness ◽  
Boundary Layer Thickness ◽  
Area Ratio ◽  
Vortex Generators ◽  
Pressure Recovery ◽  
Divergence Angle ◽  
Recovery Coefficient ◽  
Conical Diffuser ◽  
Pressure Recovery Coefficient

Vortex generators, which consist of small blades, are applied to conical diffusers the divergence angles of which are 8, 12, 16, 20, and 30 deg, respectively. The area ratio of each diffuser is four. The experiment covers the influence of various parameters, such as the arrangement of blades, inlet boundary layer thickness, and location of vortex generators relative to the conical diffuser, on the pressure-recovery coefficient. The experiment shows that the vortex generators prevent the flow in a conical diffuser from separating up to a divergence angle of 16 deg, and that the pressure-recovery coefficient is approximately equal to that of conventional best conical diffusers.

Flow Characteristics in a Large Area Ratio Curved Diffuser

1996 ◽  
Vol 210 (1) ◽  
pp. 65-75 ◽  
Author(s):  
B Majumdar ◽  
S N Singh ◽  
D P Agrawal
Keyword(s):  
Turbulence Intensity ◽  
Marked Improvement ◽  
Static Pressure ◽  
Flow Characteristics ◽  
Flow Distribution ◽  
Area Ratio ◽  
Large Area ◽  
Recovery Coefficient ◽  
Convex Wall ◽  
Pressure Recovery Coefficient

Flow characteristics in a large area ratio curved diffuser (AR = 3.4, Δβ = 90°, AS = 0.685) have been experimentally evaluated with splitter vanes installed at different angles to the flow at the inlet of the diffuser. The splitter vanes deflect the flow towards the convex wall and simultaneously increase the turbulence intensity. A marked improvement in flow distribution inside the diffuser and a significant increase in the static pressure recovery coefficient are obtained with splitter vanes at a 10° angle.

scholarly journals Effect of Area Ratio on the Performance of a 5.5:1 Pressure Ratio Centrifugal Impeller

1987 ◽  
Vol 109 (1) ◽  
pp. 10-19 ◽  
Author(s):  
L. F. Schumann ◽  
D. A. Clark ◽  
J. R. Wood
Keyword(s):  
Pressure Ratio ◽  
Velocity Ratio ◽  
Three Dimensional ◽  
Computer Code ◽  
Area Ratio ◽  
Tip Clearance ◽  
Centrifugal Impeller ◽  
Recovery Coefficient ◽  
Flow Angle ◽  
Design Point

A centrifugal impeller which was initially designed for a pressure ratio of approximately 5.5 and a mass flow rate of 0.959 kg/s was tested with a vaneless diffuser for a range of design point impeller area ratios from 2.322 to 2.945. The impeller area ratio was changed by successively cutting back the impeller exit axial width from an initial value of 7.57 mm to a final value of 5.97 mm. In all, four separate area ratios were tested. For each area ratio a series of impeller exit axial clearances was also tested. Test results are based on impeller exit surveys of total pressure, total temperature, and flow angle at a radius 1.115 times the impeller exit radius. Results of the tests at design speed, peak efficiency, and an exit tip clearance of 8 percent of exit blade height show that the impeller equivalent pressure recovery coefficient peaked at a design point area ratio of approximately 2.748 while the impeller aerodynamic efficiency peaked at a lower value of area ratio of approximately 2.55. The variation of impeller efficiency with clearance showed expected trends with a loss of approximately 0.4 points in impeller efficiency for each percent increase in exit axial tip clearance for all impellers tested. The data also indicated that the impeller would probably separate at design area ratios greater than 2.748. An analysis was performed with a quasi-three-dimensional inviscid computer code which confirmed that a minimum velocity ratio was attained near this area ratio thus indicating separation. These data can be used to verify impeller flow models which attempt to account for very high diffusion and possible separation.

Parameterization and optimization design of a two-dimensional axisymmetric hypersonic inlet

2021 ◽  
pp. 095441002110295
Author(s):  
Shangcheng Xu ◽  
Yi Wang ◽  
Zhenguo Wang ◽  
Xiaoqiang Fan ◽  
Bing Xiong
Keyword(s):  
Total Pressure ◽  
Optimization Design ◽  
Separation Bubble ◽  
Pressure Recovery ◽  
Two Dimensional ◽  
Recovery Coefficient ◽  
Hypersonic Inlet ◽  
Contraction Ratio ◽  
Total Pressure Recovery ◽  
Pressure Recovery Coefficient

Optimization method, as a promising way to improve inlet aerodynamic performance, has received increasing attention. The present research is undertaken to design a two-dimensional axisymmetric hypersonic inlet using parametric optimization. The inlet configuration is parameterized and optimized in consideration of total pressure recovery and starting performance. A Pareto front is obtained by solving the multi-objective optimization problem. Then, the flow structures of the optimized inlets are analyzed and the starting performances are evaluated. Results show that the total pressure loss mainly occurs in the internal contraction section, especially near the inlet entrance, and therefore the total pressure recovery coefficient can be greatly improved by decreasing external compression. As a result, the guidance for designing high-performance inlets is concluded. Besides, it is found that as the internal contraction ratio increases, the inlet starting ability becomes worse, which attributes to the larger separation bubble at the inlet entrance. Finally, the total pressure recovery coefficient and the starting Mach number of the optimized inlets are obtained, which can be a reference for engineering design.

scholarly journals Effect of Area Ratio on the Performance of a 5.5:1 Pressure Ratio Centrifugal Impeller

1986 ◽  
Author(s):  
Lawrence F. Schumann ◽  
David A. Clark ◽  
Jerry R. Wood
Keyword(s):  
Pressure Ratio ◽  
Velocity Ratio ◽  
Three Dimensional ◽  
Computer Code ◽  
Area Ratio ◽  
Tip Clearance ◽  
Centrifugal Impeller ◽  
Recovery Coefficient ◽  
Flow Angle ◽  
Design Point

A centrifugal impeller which was initially designed for a pressure ratio of approximately 5.5 and a mass flow rate of 0.959 kg/sec was tested with a vaneless diffuser for a range of design point impeller area ratios from 2.322 to 2.945. The impeller area ratio was changed by successively cutting back the impeller exit axial width from an initial value of 7.57 mm to a final value of 5.97 mm. In all, four separate area ratios were tested. For each area ratio a series of impeller exit axial clearances was also tested. Test results are based on impeller exit surveys of total pressure, total temperature, and flow angle at a radius 1.115 times the impeller exit radius. Results of the tests at design speed, peak efficiency, and an exit tip clearance of 8 percent of exit blade height show that the impeller equivalent pressure recovery coefficient peaked at a design point area ratio of approximately 2.748 while the impeller aerodynamic efficiency peaked at a lower value of area ratio of approximately 2.55. The variation of impeller efficiency with clearance showed expected trends with a loss of approximately 0.4 points in impeller efficiency for each percent increase in exit axial tip clearance for all impellers tested. The data also indicated that the impeller would probably separate at design area ratios greater than 2.748. An analysis was performed with a quasi-three-dimensional inviscid computer code which confirmed that a minimum velocity ratio was attained near this area ratio thus indicating separation. This data can be used to verify impeller flow models which attempt to account for very high diffusion and possible separation.

Two-Dimensional Method for Calculating Separated Flow in a Centrifugal Impeller

1975 ◽  
Vol 97 (4) ◽  
pp. 581-591 ◽  
Author(s):  
D. P. Sturge ◽  
N. A. Cumpsty
Keyword(s):  
Compressible Flow ◽  
Experimental Observation ◽  
Calculation Method ◽  
Separated Flow ◽  
Suction Side ◽  
Inviscid Flow ◽  
Centrifugal Impeller ◽  
Two Dimensional

A method of calculating a two-dimensional incompressible and inviscid flow within a centrifugal impeller where the flow separates from the suction side has been developed. Based on experimental observation it has been assumed that mixing of the throughflow with the separated region is suppressed. After a description of the calculation method, which is rather unusual, some results are presented and the implications discussed. The possibility of extending the method to handle compressible flow is outlined.

Pressure Recovery of Rotating Diffuser With Distorted Inflows

1987 ◽  
Vol 109 (2) ◽  
pp. 114-120 ◽  
Author(s):  
Koji Kikuyama ◽  
Mitsukiyo Murakami ◽  
Shin-ichi Oda ◽  
Ken-ichi Gomi
Keyword(s):  
Velocity Gradient ◽  
Rotation Speed ◽  
Suction Side ◽  
Linear Velocity ◽  
The Other ◽  
Pressure Recovery ◽  
Meridian Plane ◽  
Pressure Side ◽  
Two Dimensional ◽  
Inlet Velocity

The pressure recovery and velocity distributions in a two-dimensional rotating curved diffuser have been studied experimentally when even and uneven flows, respectively, were introduced to the diffuser. Two types of uneven flow were adopted; one has a linear velocity gradient on the surface of revolution and the other a linear velocity gradient in the meridian plane. The pressure recovery in the diffuser is improved by the unformalizing process of the uneven inlet velocities in the downstream sections if larger velocities are in the suction side region, but it is deteriorated if larger velocities are introduced in the pressure side region. When an uneven flow with a velocity gradient in the meridian plane is introduced to the diffuser, increased rotation speed and the gradient of the inlet velocity profile deteriorate the pressure recovery.

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