Secondary Flow Effects in a Bounded Rectangular Jet

1968 ◽  
Vol 90 (2) ◽  
pp. 241-248 ◽  
Author(s):  
J. F. Foss ◽  
J. B. Jones
Keyword(s):  
Aspect Ratio ◽  
Secondary Flow ◽  
Flow Structure ◽  
Flow Model ◽  
Three Dimensional ◽  
Dimensional Effects ◽  
Rectangular Jet ◽  
Secondary Flow Structure ◽  
Flow Effects

The isotach pattern in a bounded jet with an aspect ratio of 6 suggests the presence of a secondary flow structure. A physical flow model is presented, and further measurements substantiate the model and support the conclusion that three-dimensional effects are highly significant in bounded jets of modest aspect ratio, even in the mid plane between the bounding walls.

scholarly journals An Investigation of Spanwise Mixing in Multistage Axial Flow Compressors

1992 ◽  
Author(s):  
S.-M. Li ◽  
M.-Z. Chen
Keyword(s):  
Secondary Flow ◽  
Turbulent Diffusion ◽  
Flow Model ◽  
Three Dimensional ◽  
Axial Flow ◽  
Equation System ◽  
Meridional Flow ◽  
Flow Effects ◽  
Annular Cascade ◽  
Axial Flow Compressors

An equation system has been deduced for meridional throughflow fields of multistage axial flow compressors, presenting different kinds of spanwise mixing effects of the fields in a unified form. The spanwise mixing in compressors is caused by three kinds of effects, molecular motion, turbulent diffusion, and circumferential non–uniformities, the last of which includes secondary flow effects and others. This equation system thus unifies the two models for spanwise mixing analyses by Adkins & Smith (1981) and Gallimore & Cumpsty (1986). The turbulent diffusion in the two–dimensional (2–D) meridional fields is determined by complex three–dimensional (3–D) shear flows in compressors, rather than the 2–D shearing alone, so a turbulence model for 2–D meridional flow calculations is proposed on the basis of a simplified 3–D shearing structure in compressors. The circumferentially non–uniform correlation terms in the equation system have been modeled on the basis of Adkins and Smith (1981) secondary flow model and the experimental data for annular cascade wakes. The results obtained agree well with the experiments for five compressors. The results also show some improvement over the previous theories.

End-Wall Film Cooling Through Fan-Shaped Holes With Different Area Ratios

2006 ◽  
Vol 129 (2) ◽  
pp. 212-220 ◽  
Author(s):  
Giovanna Barigozzi ◽  
Giuseppe Franchini ◽  
Antonio Perdichizzi
Keyword(s):  
Secondary Flow ◽  
Mass Flow ◽  
Film Cooling ◽  
Three Dimensional ◽  
Wide Band ◽  
Lateral Spreading ◽  
Area Ratio ◽  
Adiabatic Effectiveness ◽  
Flow Effects ◽  
End Wall

The present paper reports on the aerothermal performance of a nozzle vane cascade, with film-cooled end walls. The coolant is injected through four rows of cylindrical holes with conical expanded exits. Two end-wall geometries with different area ratios have been compared. Tests have been carried out at low speed (M=0.2), with coolant to mainstream mass flow ratio varied in the range 0.5–2.5%. Secondary flow assessment has been performed through three-dimensional (3D) aerodynamic measurements, by means of a miniaturized five-hole probe. Adiabatic effectiveness distributions have been determined by using the wide-band thermochromic liquid crystals technique. For both configurations and for all the blowing conditions, the coolant share among the four rows has been determined. The aerothermal performances of the cooled vane have been analyzed on the basis of secondary flow effects and laterally averaged effectiveness distributions; this analysis was carried out for different coolant mass flow ratios. It was found that the smaller area ratio provides better results in terms of 3D losses and secondary flow effects; the reason is that the higher momentum of the coolant flow is going to better reduce the secondary flow development. The increase of the fan-shaped hole area ratio gives rise to a better coolant lateral spreading, but appreciable improvements of the adiabatic effectiveness were detected only in some regions and for large injection rates.

Separating and Reattaching Flow Structure in a Suddenly Expanding Rectangular Duct

1995 ◽  
Vol 117 (1) ◽  
pp. 17-23 ◽  
Author(s):  
G. Papadopoulos ◽  
M. V. O¨tu¨gen
Keyword(s):  
Aspect Ratio ◽  
Flow Structure ◽  
Three Dimensional ◽  
Side Wall ◽  
Stream Velocity ◽  
Rectangular Duct ◽  
Mean Flow ◽  
Wall Effects ◽  
Velocity Measurements ◽  
Aspect Ratios

The incompressible turbulent flow over a backward-facing step in a rectangular duct was investigated experimentally. The side wall effects on the core flow were determined by varying the aspect ratio (defined as the step span-to-height ratio) from 1 to 28. The Reynolds number, based on the step height and the oncoming free-stream velocity, was 26,500. Detailed velocity measurements were made, including the turbulent stresses, in a region which extended past the flow reattachment zone. Wall static pressure was also measured on both the step and flat walls. In addition, surface visualizations were obtained on all four walls surrounding the separated flow to supplement near-wall velocity measurements. The results show that the aspect ratio has an influence on both the velocity and wall pressure even for relatively large aspect ratios. For example, in the redevelopment region downstream of reattachment, the recovery pressure decreases with smaller aspect ratios. The three-dimensional side wall effects tend to slow down the relaxation downstream of reattachment for smaller aspect ratios as evidenced by the evolution of the velocity field. For the two smallest aspect ratios investigated, higher centerplane streamwise and transverse velocities were obtained which indicate a three-dimensional mean flow structure along the full span of the duct.

A Geometry Generation Framework for Contoured Endwalls

2019 ◽  
Author(s):  
L. E. Wood ◽  
R. R. Jones ◽  
O. J. Pountney ◽  
J. A. Scobie ◽  
D. A. S. Rees ◽  
...  
Keyword(s):  
Secondary Flow ◽  
Three Dimensional ◽  
Aerodynamic Loss ◽  
Construction Methods ◽  
Novel Approach ◽  
Wide Range ◽  
Blade Row ◽  
Flow Features ◽  
Flow Effects ◽  
Geometric Variation

Abstract The mainstream, or primary, flow in a gas turbine annulus is characteristically two-dimensional over the mid-span region of the blading, where the radial flow is almost negligible. Contrastingly, the flow in the endwall and tip regions of the blading is highly three-dimensional, characterised by boundary layer effects, secondary flow features and interaction with cooling flows. Engine designers employ geometric contouring of the endwall region in order to reduce secondary flow effects and subsequently minimise their contribution to aerodynamic loss. Such is the geometric variation of vane and blade profiles — which has become a proprietary art form — the specification of an effective endwall geometry is equally unique to each blade-row. Endwall design methods, which are often directly coupled to aerodynamic optimisers, are widely developed to assist with the generation of contoured surfaces. Most of these construction methods are limited to the blade-row under investigation, while few demonstrate the controllability required to offer a universal platform for endwall design. This paper presents a Geometry Generation Framework (GGF) for the generation of contoured endwalls. The framework employs an adaptable meshing strategy, capable of being applied to any vane or blade, and a versatile function-based approach to defining the endwall shape. The flexibility of this novel approach is demonstrated by recreating a selection of endwalls from the literature, which were selected for their wide-range of contouring approaches.

Nekomimi Film Cooling Holes Configuration Under Conjugate Heat Transfer Conditions

2014 ◽  
Author(s):  
Karsten Kusterer ◽  
Nurettin Tekin ◽  
Tobias Wüllner ◽  
Dieter Bohn ◽  
Takao Sugimoto ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Conduction ◽  
Secondary Flow ◽  
Flow Structure ◽  
Film Cooling ◽  
Conjugate Heat Transfer ◽  
Cooling Effectiveness ◽  
Cooling Flow ◽  
Secondary Flow Structure ◽  
Cooling Air

In modern gas turbines, the film cooling technology is essential for the protection of the hot parts, in particular of the first stage vanes and blades of the turbine, against the hot gases from the combustion process in order to reach an acceptable life span of the components. As the cooling air is usually extracted from the compressor, the reduction of the cooling effort would directly result in increased thermal efficiency of the gas turbine. Understanding of the fundamental physics of film cooling is necessary for the improvement of the state-of-the-art. Thus, huge research efforts by industry as well as research organizations have been undertaken to establish high efficient film cooling technologies. Today it is common knowledge that film cooling effectiveness degradation is caused by secondary flows inside the cooling jets, i.e. the Counter-Rotating Vortices (CRV) or sometimes also called kidney-vortices, which induce a lift-off of the jet. Further understanding of the secondary flow development inside the jet and how this could be influenced, has led to hole configurations, which can induce Anti-Counter-Rotating Vortices (ACRV) in the cooling jets. As a result, the cooling air remains close to the wall and is additionally distributed flatly along the surface. Beside different other technologies, the NEKOMIMI cooling technology is a promising approach to establish the desired ACRVs. It consists of a combination of two holes in just one configuration so that the air is distributed mainly on two cooling air streaks following the special shape of the generated geometry. The NEKOMIMI configuration and two conventional cooling hole configurations (cylindrical and shaped holes) has been investigated numerically under adiabatic and conjugate heat transfer conditions. The influence of the conjugate heat transfer on the secondary flow structure has been analysed. In conjugate heat transfer calculations, it cannot directly derived from the surface temperature distribution if the reached cooling effectiveness values are due to the improved hole configuration with improved secondary flow structure or due to the heat conduction in the material. Therefore, a methodology has been developed, to distinguish between cooling effectiveness due to heat conduction in the material and film cooling flow over the surface. The numerical results shows that for the NEKOMIMI configuration, 77% of the reached overall cooling effectiveness is due to film cooling with improved flow structure in the secondary flow (ACRV) and 23% due to heat conduction in the material. For the cylindrical hole configuration, 10% of the reached overall cooling effectiveness is due to the film cooling flow structure and 90% due to heat conduction in the material.

scholarly journals Secondary Flow Effects and Mixing of the Wake Behind a Turbine Stator

1982 ◽  
Author(s):  
A. Binder ◽  
R. Romey
Keyword(s):  
Secondary Flow ◽  
Flow Direction ◽  
Three Dimensional ◽  
Detailed Knowledge ◽  
Pressure Loss Coefficient ◽  
Turbine Stator ◽  
Dimensional Measurements ◽  
Order Of Magnitude ◽  
Flow Effects ◽  
Secondary Vortices

In highly loaded turbines with large hub/tip ratios there is a marked increase in secondary flow effects. The optimization of the turbine flow requires detailed knowledge both of three-dimensional cascade flow and of the wake impinging on the downstream rows of airfoils. Therefore, in the DFVLR, thorough investigations of a single-stage turbine with cold air flow were performed. The stator of this turbine was designed for transonic flow and has a hub/tip ratio of 0.756 and an aspect ratio of 0.56. First, measurements were taken without the rotor in several sections behind the turbine stator with special regard to the mixing of the wakes and secondary vortices. Distributions of total pressure loss coefficient and flow direction give the order of magnitude of the mixing losses. Also, position, intensity, structure, and development of secondary vortices are shown. Some complementary measurements were carried out using five-hole probes. They confirm the above described results from two-dimensional measurements.

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