Influence of Chord Length and Inlet Boundary Layer on the Secondary Losses of Turbine Blades

2011 ◽  
Vol 134 (1) ◽  
Author(s):  
Helmut Sauer ◽  
Robin Schmidt ◽  
Konrad Vogeler
Keyword(s):  
Boundary Layer ◽  
Layer Thickness ◽  
Boundary Layer Thickness ◽  
Flow Direction ◽  
Velocity Ratio ◽  
Main Flow ◽  
Chord Length ◽  
Displacement Thickness ◽  
Wide Range ◽  
Main Flow Direction

In this paper, results concerning the influence of chord length and inlet boundary layer thickness on the endwall loss of a linear turbine cascade are discussed. The investigations were performed in a low speed cascade tunnel using the turbine profile T40. The turning of 90 deg and 70 deg, the velocity ratio in the cascade from 1.0 to 3.5 as well as the chord length of 100 mm, 200 mm, and 300 mm were specified. In a measurement distance of one chord behind the cascade in main flow direction, an approximate proportionality of endwall loss and chord was observed in a wide range of velocity ratios. At small measurement distances (e.g., s2/l=0.4), this proportionality does not exist. If a part of the flow path within the cascade is approximately incorporated, a proportionality to the chord at small measurement distances can be obtained, too. Then, the magnitude of the endwall loss mainly depends on the distance in main flow direction. At velocity ratios near 1.0, the influence of the chord decreases rapidly, while at a velocity ratio of 1.0, the endwall loss is independent of the chord. By varying the inlet boundary layer thickness, no correlation of displacement thickness and endwall loss was achieved. A calculation method according to the modified integral equation by van Driest delivers the wall shear stress. Its influence on the endwall loss was analyzed.

Influence of Chord Length and Inlet Boundary Layer on the Secondary Losses of Turbine Blades

2010 ◽  
Author(s):  
Helmut Sauer ◽  
Robin Schmidt ◽  
Konrad Vogeler
Keyword(s):  
Boundary Layer ◽  
Layer Thickness ◽  
Boundary Layer Thickness ◽  
Flow Direction ◽  
Velocity Ratio ◽  
Turbine Blades ◽  
Flow Path ◽  
Chord Length ◽  
Displacement Thickness ◽  
Wide Range

In the present paper results concerning the influence of chord length and inlet boundary layer thickness on the endwall losses are discussed. The investigations were performed in a low speed cascade tunnel using the turbine profile T40. The deflection of 90 and 70 deg, the velocity ratio in the cascade from 1.0 to 3.5 as well as the chord length of 100,200 and 300 mm were predetermined. In a measurement distance behind the cascade of s2/l = 1, an approximate proportionality of endwall losses and chord length was observed in a wide range of velocity ratios. At small measurement distances (e.g. s2/l = 0.4), this proportionality does not exist. If aside from the flow path behind the cascade the flow path in the cascade is approximately incorporated, a proportionality to the chord length at small measurement distances can be obtained, too. Then to a large extent, the magnitude of the endwall losses is dependent on the length in main flow direction. At velocity ratios near 1.0, the influence of the chord length decreases rapidly, while at a velocity ratio of 1.0, the endwall losses are independent of chord length. By varying the inlet boundary layer thickness no correlation of displacement thickness and endwall losses was achieved. With a calculation method according to the modified integral equation by van Driest, the velocity gradient on the wall, the wall shear stress and the local friction coefficient were determined and their influence on the endwall losses analyzed.

Experimental Flow Structure Analysis in Plates With 90° Chevron Geometry by a Particle Visualization Technique

2007 ◽  
Author(s):  
Jose M. Luna ◽  
Ricardo Romero-Mendez ◽  
Abel Hernandez-Guerrero ◽  
Jose C. Rubio-Arana
Keyword(s):  
Flow Direction ◽  
Main Flow ◽  
Flow Structures ◽  
Visualization Technique ◽  
Corrugated Surfaces ◽  
Wide Range ◽  
Main Flow Direction ◽  
Corrugated Plates ◽  
Visualization Experiments ◽  
Particle Visualization

The flow structures in the cavities of parallel cross-corrugated surfaces, also called chevron geometry, are investigated in this work using an experimental visualization method. An angle of 45° between the corrugations and the main flow direction has been considered. Reviews show that a considerable amount of investigations, mainly experimental, of heat transfer and pressure drop for cross-corrugated plates has been performed, whereas for the flow field in the cavities has only been investigated numerically. The flow visualization experiments are performed inside a water tunnel using a wide range of the hydraulic diameter-based Reynolds number.

Wind-Tunnel Screens: Flow Instability and its Effect on Aerofoil Boundary Layers

1964 ◽  
Vol 68 (639) ◽  
pp. 198-198 ◽  
Author(s):  
P. Bradshaw
Keyword(s):  
Boundary Layer ◽  
Wind Tunnel ◽  
Layer Thickness ◽  
Boundary Layers ◽  
Boundary Layer Thickness ◽  
Flow Instability ◽  
Flow Direction ◽  
Flat Plates ◽  
Mixing Processes ◽  
Flow Through

Morgan has described a spatial instability in the flow through screens or grids of small open-area ratio. Head and Rechenberg and others have observed large span-wise variations in the thickness and shear stress of nominally two-dimensional boundary layers on flat plates and aerofoils in wind tunnels. It now appears that these spanwise variations are caused by the instability of flow through the screens. The jets of air issuing from the pores of the screen attempt to entrain more air by the usual mixing processes, but can only entrain it from each other, so that groups of jets coalesce in rather random (steady) patterns determined by small irregularities in the weave. The resulting variations in axial velocity are virtually eliminated by the wind tunnel contraction, but variations in flow direction are not so greatly reduced: a theoretical analysis shows that the observed variations of boundary-layer thickness, which often reach ± 10 per cent of the mean, can be produced by directional variations in the working section of the order of ± 1/20 deg, with a spanwise wavelength of the same order as the boundary-layer thickness.

scholarly journals MHD Stagnation-Point Flow of Casson Fluid and Heat Transfer over a Stretching Sheet with Thermal Radiation

2013 ◽  
Vol 2013 ◽  
pp. 1-9 ◽  
Author(s):  
Krishnendu Bhattacharyya
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Thermal Radiation ◽  
Layer Thickness ◽  
Boundary Layer Thickness ◽  
Stretching Sheet ◽  
Magnetic Parameter ◽  
Velocity Ratio ◽  
Casson Fluid ◽  
Velocity Boundary Layer

The two-dimensional magnetohydrodynamic (MHD) stagnation-point flow of electrically conducting non-Newtonian Casson fluid and heat transfer towards a stretching sheet have been considered. The effect of thermal radiation is also investigated. Implementing similarity transformations, the governing momentum, and energy equations are transformed to self-similar nonlinear ODEs and numerical computations are performed to solve those. The investigation reveals many important aspects of flow and heat transfer. If velocity ratio parameter (B) and magnetic parameter (M) increase, then the velocity boundary layer thickness becomes thinner. On the other hand, for Casson fluid it is found that the velocity boundary layer thickness is larger compared to that of Newtonian fluid. The magnitude of wall skin-friction coefficient reduces with Casson parameter (β). The velocity ratio parameter, Casson parameter, and magnetic parameter also have major effects on temperature distribution. The heat transfer rate is enhanced with increasing values of velocity ratio parameter. The rate of heat transfer is enhanced with increasing magnetic parameter M for B > 1 and it decreases with M for B < 1. Moreover, the presence of thermal radiation reduces temperature and thermal boundary layer thickness.

Effects of a Source-Type Hypersonic Free Stream on the Flow Field about an Axisymmetric Cone

1966 ◽  
Vol 17 (2) ◽  
pp. 161-176
Author(s):  
Stuart B. Savage
Keyword(s):  
Boundary Layer ◽  
Flow Field ◽  
Layer Thickness ◽  
Surface Pressure ◽  
Shock Layer ◽  
Boundary Layer Thickness ◽  
Free Stream ◽  
Inviscid Flow ◽  
Source Type ◽  
Displacement Thickness

SummaryMost hypervelocity tunnels presently make use of conical or wedge type nozzles which produce source-type flow non-uniformities in the test section. The present paper considers the effects of such free-stream non-uniformities on the flow fields about slender axisymmetric cones. The inviscid flow is considered within the framework of the Newtonian expansion procedure of Cole and simple expressions are obtained for the flow field properties in the shock layer. This inviscid analysis predicts that a free-stream gradient of a magnitude typical of present hypervelocity test facilities can cause sizeable reductions in surface pressure and increased shock-layer thickness at the aft end of long slender conical models. The cone pressure, accounting for the viscous-inviscid interaction, is obtained by applying the inviscid analysis in tangent-cone fashion to the effective body (i.e. physical cone plus boundary-layer displacement thickness). Cheng’s simple equation is used to approximate the hypersonic boundary-layer development. Large increases in the boundary-layer thickness at the aft end of the model are predicted as a consequence of the source flow effects. The analyses agree well with experimental measurements of surface pressure and boundary-layer thickness made on a 5° half-angle cone tested in the Republic 24 inch Longshot I hypervelocity shock tunnel.

scholarly journals BOTTOM TURBULENT BOUNDARY LAYER IN WAVE-CURRENT CO-EXISTING SYSTEMS

1984 ◽  
Vol 1 (19) ◽  
pp. 161 ◽  
Author(s):  
Toshiuki Asano ◽  
Yuichi Iwagaki
Keyword(s):  
Boundary Layer ◽  
Mathematical Method ◽  
Turbulent Boundary Layer ◽  
Layer Thickness ◽  
Particle Velocity ◽  
Boundary Layer Thickness ◽  
Velocity Ratio ◽  
Laser Doppler Velocimeter ◽  
Unknown Boundary ◽  
Water Particle

This study presents a new mathematical method calculating the water particle velocity in the wave-current co-existing systems. A boundary layer thickness 5,„ in the co-existing system is expected to be variable with the water particle velocity ratio of wave component to current component. In this method, the boundary layer equation is solved as a free boundary problem by treating 6,„ as an unknown boundary value. Several characteristics of the turbulent boundary layer such as the friction factor, friction velocity, boundary layer thickness, etc. are calculated by this method and the effect of the wave-current velocity ratio on them is discussed. Furthermore, the velocity reduction of the current due to wave superimposing is investigated. In addition, near-bottom velocities are measured by a laser-doppler velocimeter in the pure current, the pure wave and the wave-current co-existing fields. These results are compared with calculated ones by this mathematical method.

Self-consistent unstirred layers in osmotically driven flows

2010 ◽  
Vol 662 ◽  
pp. 197-208 ◽  
Author(s):  
K. H. JENSEN ◽  
T. BOHR ◽  
H. BRUUS
Keyword(s):  
Boundary Layer ◽  
Layer Thickness ◽  
Boundary Layers ◽  
Boundary Layer Thickness ◽  
Concentration Boundary ◽  
Concentration Boundary Layers ◽  
Unstirred Layers ◽  
Mathematical Relation ◽  
Wide Range ◽  
Self Consistent

It has long been recognized that the osmotic transport characteristics of membranes may be strongly influenced by the presence of unstirred concentration boundary layers adjacent to the membrane. Previous experimental as well as theoretical works have mainly focused on the case where the solutions on both sides of the membrane remain well mixed due to an external stirring mechanism. We investigate the effects of concentration boundary layers on the efficiency of osmotic pumping processes in the absence of external stirring, i.e. when all advection is provided by the osmosis itself. This case is relevant in the study of intracellular flows, e.g. in plants. For such systems, we show that no well-defined boundary-layer thickness exists and that the reduction in concentration can be estimated by a surprisingly simple mathematical relation across a wide range of geometries and Péclet numbers.

Experimental Investigation of Film Cooling With Ejection From a Row of Holes for the Application to Gas Turbine Blades

1975 ◽  
Vol 97 (1) ◽  
pp. 21-27 ◽  
Author(s):  
C. Liess
Keyword(s):  
Boundary Layer ◽  
Gas Turbine ◽  
Velocity Ratio ◽  
Turbine Blades ◽  
Main Flow ◽  
Adiabatic Wall ◽  
Lateral Direction ◽  
Gas Turbine Blades ◽  
Flow Boundary ◽  
Displacement Thickness

The adiabatic wall effectiveness and the heat transfer coefficient is determined experimentally on a flat plate downstream of a row of inclined circular ejection holes. The measuring technique provides local values in downstream direction and averaged values in lateral direction. The ejection geometry is kept constant, i.e., ejection angle β = 35 deg, spacing to diameter ratio of ejection holes s/d = 3. The range of flow parameters corresponds closely to the conditions encountered on gas turbine blades. The main flow Mach number varies from 0.3 to 0.9, the mass velocity ratio from 0.1 to 2.0. Two favorable pressure gradients in the main flow are applied and several ratios of main flow boundary layer displacement thickness to ejection hole diameter. The main flow boundary layer upstream of the ejection is laminar and turbulent.

scholarly journals Improvement of the Full-Range Equation for Wave Boundary Layer Thickness

2020 ◽  
Vol 8 (8) ◽  
pp. 573 ◽  
Author(s):  
Hitoshi Tanaka ◽  
Nguyen Xuan Tinh ◽  
Ahmad Sana
Keyword(s):  
Boundary Layer ◽  
Layer Thickness ◽  
Boundary Layer Thickness ◽  
Full Range ◽  
Tsunami Waves ◽  
Wave Boundary Layer ◽  
Wide Range ◽  
Range Equation ◽  
Wave Boundary ◽  
Flow Experiments

In order to improve the accuracy of the original full-range equation for wave boundary layer thickness, with special reference to increasing its applicability to tsunami-scale waves, a theoretical investigation is carried out to derive a dimensionless expression which is valid under both smooth and rough turbulent regimes. A coefficient in the equation is determined through a comparison with k-ω  model computation results for tsunami-waves along with laboratory scale oscillatory flow experiments. Thus, the improved full-range equation for wave boundary layer thickness enables us to cover a wide range of wave periods from wind-wave to tsunami.

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