Influence of Turbulent Flow Characteristics and Coherent Vortices on the Pressure Recovery of Annular Diffusers: Part A — Experimental Results

2015 ◽  
Author(s):  
Marcus Kuschel ◽  
Bastian Drechsel ◽  
David Kluß ◽  
Joerg R. Seume
Keyword(s):  
Boundary Layer ◽  
High Pressure ◽  
Static Pressure ◽  
Turbulent Transport ◽  
Axial Flow ◽  
Pressure Recovery ◽  
Turbulence Structure ◽  
Reynolds Stresses ◽  
Wide Range ◽  
Operating Points

Exhaust diffusers downstream of turbines are used to transform the kinetic energy of the flow into static pressure. The static pressure at the turbine outlet is thus decreased by the diffuser, which in turn increases the technical work as well as the efficiency of the turbine significantly. Consequently, diffuser designs aim to achieve high pressure recovery at a wide range of operating points. Current diffuser design is based on conservative design charts, developed for laminar, uniform, axial flow. However, several previous investigations have shown that the aerodynamic loading and the pressure recovery of diffusers can be increased significantly if the turbine outflow is taken into consideration. Although it is known that the turbine outflow can reduce boundary layer separations in the diffuser, less information is available regarding the physical mechanisms that are responsible for the stabilization of the diffuser flow. An analysis using the Lumley invariance charts shows that high pressure recovery is only achieved for those operating points in which the near-shroud turbulence structure is axi-symmetric with a major radial turbulent transport component. This turbulent transport originates mainly from the wake and the tip vortices of the upstream rotor. These structures energize the boundary layer and thus suppress separation. A logarithmic function is shown that correlates empirically the pressure recovery vs. the relevant Reynolds stresses. The present results suggest that an improved prediction of diffuser performance requires modeling approaches that account for the anisotropy of turbulence.

The response of a turbulent boundary layer to lateral divergence

1979 ◽  
Vol 94 (2) ◽  
pp. 243-268 ◽  
Author(s):  
A. J. Smits ◽  
J. A. Eaton ◽  
P. Bradshaw
Keyword(s):  
Boundary Layer ◽  
Circular Cylinder ◽  
Turbulent Boundary Layer ◽  
Structural Parameters ◽  
Axial Flow ◽  
Turbulence Structure ◽  
Two Dimensional ◽  
Transition Section ◽  
Two Dimensional Flow ◽  
Made In

Measurements have been made in the flow over an axisymmetric cylinder-flare body, in which the boundary layer developed in axial flow over a circular cylinder before diverging over a conical flare. The lateral divergence, and the concave curvature in the transition section between the cylinder and the flare, both tend to destabilize the turbulence. Well downstream of the transition section, the changes in turbulence structure are still significant and can be attributed to lateral divergence alone. The results confirm that lateral divergence alters the structural parameters in much the same way as longitudinal curvature, and can be allowed for by similar empirical formulae. The interaction between curvature and divergence effects in the transition section leads to qualitative differences between the behaviour of the present flow, in which the turbulence intensity is increased everywhere, and the results of Smits, Young & Bradshaw (1979) for a two-dimensional flow with the same curvature but no divergence, in which an unexpected collapse of the turbulence occurred downstream of the curved region.

Validation of MISES Two-Dimensional Boundary Layer Code for High-Pressure Turbine Aerodynamic Design

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
Philip L. Andrew ◽  
Harika S. Kahveci
Keyword(s):  
Boundary Layer ◽  
High Pressure ◽  
Operating Cost ◽  
Design Tool ◽  
Operating Conditions ◽  
Aerodynamic Design ◽  
High Pressure Turbine ◽  
Reduce Operating Cost ◽  
Wide Range ◽  
Dimensional Boundary

Avoiding aerodynamic separation and excessive shock losses in gas turbine turbomachinery components can reduce fuel usage and thus reduce operating cost. In order to achieve this, blading designs should be made robust to a wide range of operating conditions. Consequently, a design tool is needed—one that can be executed quickly for each of many operating conditions and on each of several design sections, which will accurately capture loss, turning, and loading. This paper presents the validation of a boundary layer code, MISES, versus experimental data from a 2D linear cascade approximating the performance of a moderately loaded mid-pitch section from a modern aircraft high-pressure turbine. The validation versus measured loading, turning, and total pressure loss is presented for a range of exit Mach numbers from ≈0.5 to 1.2 and across a range of incidence from −10 deg to +14.5 deg relative to design incidence.

Effects of Inlet Conditions on the Flow in a Fishtail Curved Diffuser With Strong Curvature

1996 ◽  
Vol 118 (4) ◽  
pp. 772-778 ◽  
Author(s):  
M. I. Yaras
Keyword(s):  
Boundary Layer ◽  
Velocity Field ◽  
Large Scale ◽  
Static Pressure ◽  
Pressure Recovery ◽  
Centrifugal Impeller ◽  
Flow Development ◽  
Diffuser Flow ◽  
Inlet Conditions ◽  
Strong Curvature

The paper presents detailed measurements of the incompressible flow at the exit of a large-scale 90-degree curved diffuser with strong curvature and significant stream-wise variation in the cross-section aspect ratio. The diffuser flow path approximates the so-called fish-tail diffuser utilized on small gas turbine engines for the transition between the centrifugal impeller and the combustion chamber. Five variations of the inlet boundary layer are considered. The results provide insight into several aspects of the diffuser flow including: the effect of flow turning on diffusion performance; the dominant structures influencing the flow development in the diffuser; and the effect of the inlet boundary layer integral parameters on the diffusion performance and the exit velocity field. The three-dimensional velocity distribution at the diffuser exit is found to be sensitive to circumferentially uniform alterations to the inlet boundary layer. In contrast, circumferential variations in the inlet boundary layer are observed to have only secondary effects on the velocity field at the diffuser exit. The static pressure recovery is observed to be comparable to the published performance of conical diffusers with equivalent included angle and area ratios. Furthermore, both the static pressure recovery and the total pressure losses are observed to be relatively insensitive to variations in the inlet boundary layer. The physical mechanisms dominating the flow development in the diffuser are discussed in light of these observations.

Full-coverage film cooling. Part 1. Three-dimensional measurements of turbulence structure

1980 ◽  
Vol 101 (1) ◽  
pp. 129-158 ◽  
Author(s):  
S. Yavuzkurt ◽  
R. J. Moffat ◽  
W. M. Kays
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Film Cooling ◽  
Outer Boundary ◽  
Turbulence Structure ◽  
Reynolds Stresses ◽  
Mean Velocity ◽  
Test Plate ◽  
Apparent Paradox ◽  
Full Coverage

Hydrodynamic measurements were made with a triaxial hot wire in the full-coverage region and the recovery region following an array of injection holes inclined downstream, at 30° to the surface. The data were taken under isothermal conditions at ambient temperature and pressure for two blowing ratios: M = 0·9 and M = 0·4. (The ratio M = ρjetUjet/ρ∞U∞, where U is the mean velocity and ρ is the density. Subscripts jet and ∞ stand for injectant and free stream, respectively.) Profiles of the three mean-velocity components and the six Reynolds stresses were obtained at several spanwise positions at each of five locations down the test plate.In the full-coverage region, high levels of turbulence kinetic energy (TKE) were found for low blowing and low TKE levels for high blowing. This observation is especially significant when coupled with the fact that the heat transfer coefficient is high for high blowing, and low for low blowing. This apparent paradox can be resolved by the hypothesis that entrainment of the mainstream fluid must be more important than turbulent mixing in determining the heat transfer behaviour at high blowing ratios (close to unity).In the recovery region, the flow can be described in terms of a two-layer model: an outer boundary layer and a two-dimensional inner boundary layer. The inner layer governs the heat transfer.

Highly-Loaded Low-Reaction Boundary Layer Suction Axial Flow Compressor

2007 ◽  
Author(s):  
Songtao Wang ◽  
Xiaoqing Qiang ◽  
Weichun Lin ◽  
Guotai Feng ◽  
Zhongqi Wang
Keyword(s):  
Boundary Layer ◽  
High Pressure ◽  
Pressure Ratio ◽  
Axial Flow ◽  
Design Concept ◽  
Axial Flow Compressor ◽  
Boundary Layer Suction ◽  
High Pressure Ratio ◽  
Flow Compressor ◽  
Highly Loaded

In order to design high pressure ratio and highly loaded axial flow compressor, a new design concept based on Highly-Loaded Low-Reaction and boundary layer suction was proposed in this paper. Then the concept’s characteristics were pointed out by comparing with the MIT’s boundary layer suction compressor. Also the application area of this design concept and its key technic were given out in this paper. Two applications were carried out in order to demonstrate the concept. The first application was to redesign a low speed duplication-stage axial flow compressor into a single stage. The second one was a feasibility analysis to decrease an 11 stage axial compressor’s stage count to 7 while not changing its aerodynamic performance. The analysis result showed that the new design concept is feasible and it can be used on high pressure stage of the aero-engine, compressor of ground gas turbine (except the transonic stage) and high total pressure ratio blower.

Factors Affecting the Performance of the Supersonic Parallel Diffuser

1966 ◽  
Vol 8 (1) ◽  
pp. 62-69 ◽  
Author(s):  
B. W. Martin
Keyword(s):  
Static Pressure ◽  
Pressure Ratio ◽  
Area Ratio ◽  
Stagnation Pressure ◽  
Pressure Recovery ◽  
Cross Sectional ◽  
Factors Affecting ◽  
Single Shock ◽  
Wide Range

Following the work of Baker and Martin (1), this paper provides further information about static pressure recovery in axi-symmetric supersonic parallel diffusers of fixed length and the same upstream generating nozzle when the diffuser cross-sectional area is varied over a wide range. Correlations based on these and associated experiments by Martin and Baker (2) indicate an area ratio for maximum possible static pressure recovery. At breakdown of the single shock, the diffuser stagnation pressure ratio corresponds to that for normal shock pressure recovery, while the outlet Mach number becomes independent of area ratio as the latter increases. The factors which influence the development and stability of the single shock regime are considered in some detail, from which the role of the boundary layer is shown to be predominant.

scholarly journals Lichtabsorption von oxidischen Silber(I)-Verbindungen / Light Absorption of Silver(I)-oxides

1984 ◽  
Vol 39 (6) ◽  
pp. 739-743 ◽  
Author(s):  
Claus Friebel ◽  
Martin Jansen
Keyword(s):  
High Pressure ◽  
Charge Transfer ◽  
Low Temperature ◽  
Absorption Edge ◽  
Diffuse Reflectance ◽  
Static Pressure ◽  
Ambient Pressure ◽  
Partial Structures ◽  
Wide Range ◽  
Charge Transfer Transitions

AbstractDiffuse reflectance spectra of Ag2SO4, Ag3PO4, Ag2CO3, Ag2Ge2O5, AgBO2, Ag3BO3-II, Ag6Si2O7, Ag10Si4O13 and Ag10Ge4O13 in the region ν̄ = 10000-40000 cm-1 and generally at 298 K and ambient pressure were measured. Additional spectra were recorded at 5 K for Ag3BO3 and Ag3PO4, and under application of a static pressure of 80 kbar for Ag10Si4O13. As a common feature all spectra show a steep absorption edge, which is only structured in singular cases. The edges appear in the remarkably wide range from 33100 cm-1 (Ag2SO4) to 13500 cm-1 (Ag10Ge4O13). As the shifts correlate with the dimensions of the cluster-like silver partial structures, the absorptions have been attributed to 4d→5s band-band transitions, an interpretation, which is in agreement with the low temperature and high pressure spectra. However, effects originating from charge-transfer transitions cannot be absolutely excluded.

scholarly journals Experimental Investigation on Ducted Counter-Rotating Axial Flow Fans

2011 ◽  
Author(s):  
Hussain Nouri ◽  
Florent Ravelet ◽  
Farid Bakir ◽  
Christophe Sarraf
Keyword(s):  
Inverse Method ◽  
Pressure Fluctuations ◽  
Axial Flow ◽  
Axial Distance ◽  
Large Patch ◽  
Rotation Rates ◽  
Wall Pressure Fluctuations ◽  
Wide Range ◽  
High Efficient ◽  
Operating Points

An experimental study on counter-rotating axial-flow fans was carried out. The fans of diameter D = 375 mm were designed using an inverse method. The counter-rotating fans operate in a ducted-flow configuration and the overall performances are measured in a normalized test bench. The rotation rate of each fan is independently controlled. The axial spacing between the fans can vary from 10 to 50 mm by steps of 10 mm. The results show that the efficiency is strongly increased compared to a conventional rotor or to a rotor-stator stage. The effects of varying the rotation rates ratio on the overall performances are studied and show that the system is highly efficient on a wide range of flow-rates and pressure rises. However, the change of the axial distance between rotors from 10 to 50 mm does not seem to change the overall performances. This system has thus a very flexible use, with a large patch of high efficient operating points in the parameter space. Further local studies including velocity measurements and wall-pressure fluctuations in the space between the rotors are needed to better understand the interactions between the rotors and to optimize the system.

Subsonic Pressure Recovery in Cylindrical Condensers

1989 ◽  
Vol 111 (2) ◽  
pp. 533-537 ◽  
Author(s):  
C. A. Busse ◽  
R. I. Loehrke
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Power Series ◽  
Subsonic Flow ◽  
Axial Flow ◽  
Pressure Recovery ◽  
Wall Friction ◽  
Turbulent Regime ◽  
Boundary Layer Approximation ◽  
Absolute Value

A method is presented for predicting laminar, subsonic flow in axisymmetric cylindrical heat pipe condensers. The method involves the use of the boundary layer approximation and a noncontinuous power series to describe the velocity profile under conditions including strong axial flow reversal. A comparison between laminar predictions and measurements indicates that transition to turbulent flow in the condenser begins when the absolute value of the radial Reynolds number exceeds 6. The condenser pressure recovery in the turbulent regime can be calculated from the momentum flow at the condenser inlet and an empirical wall-friction parameter.

Premature boundary layer transition caused by surface static pressure tappings

1988 ◽  
Vol 92 (912) ◽  
pp. 63-68 ◽  
Author(s):  
P. E. Roach ◽  
J. T. Turner
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Reynolds Number ◽  
Circular Cylinder ◽  
Static Pressure ◽  
Cross Flow ◽  
Boundary Layer Transition ◽  
Layer Transition ◽  
Wide Range ◽  
Boundary Layer Interaction

Summary Experiments have been performed to study the influence of multiple surface static pressure tappings on transition of the boundary layer on a circular cylinder in cross-flow. A wide range of tapping and cylinder dimensions have been examined to demonstrate that the tappings can act in the same way as trip wires or other surface roughness to reduce the Reynolds number at which transition occurs. Hence, the pressure distribution around the cylinder may be influenced by the presence of the tappings, leading to incorrect measurements. Examination of the data has resulted in a correlation which should make it possible to avoid this tapping/boundary layer interaction in future experiments involving similar cylindrical bodies.

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