Secondary Flow in Rotating Bends

1978 ◽  
Vol 100 (4) ◽  
pp. 553-560 ◽  
Author(s):  
M. W. Johnson
Keyword(s):  
Boundary Layer ◽  
Finite Difference ◽  
Secondary Flow ◽  
Flow Rate ◽  
Rotational Speed ◽  
Total Pressure ◽  
Secondary Flows ◽  
Streamwise Vorticity ◽  
Inlet Distortion ◽  
Finite Difference Techniques

An equation describing the development of streamwise vorticity is derived. The fluid is assumed inviscid and incompressible and to have a gradient of rotating total pressure across the streamtube. The equation is used to calculate, by finite difference techniques, the streamwise vorticity development for bends, rotating straight pipes, rotating axial to radial bends and for a rotating duct representing Eckardt’s impeller passage. The development of secondary flows in centrifugal compressors is discussed. It is concluded that the secondary flows within the boundary layer determine the position of the wake at outlet and probably influence separation. It is also concluded that the wake can be moved by altering mass flow rate, rotational speed or by introducing an inlet distortion to the flow.

On the definition of the secondary flow in three-dimensional cascades

2009 ◽  
Vol 223 (6) ◽  
pp. 667-676 ◽  
Author(s):  
G Persico ◽  
P Gaetani ◽  
V Dossena ◽  
G D'Ippolito ◽  
C Osnaghi
Keyword(s):  
Boundary Layer ◽  
Flow Field ◽  
Secondary Flow ◽  
Boundary Layers ◽  
Complex Geometry ◽  
Flow Direction ◽  
Flow Analysis ◽  
Secondary Flows ◽  
Streamwise Vorticity ◽  
Reference Flow

The present article proposes a novel methodology to evaluate secondary flows generated by the annulus boundary layers in complex cascades. Unlike two-dimensional (2D) linear cascades, where the reference flow is commonly defined as that measured at midspan, the problem of the reference flow definition for annular or complex 3D linear cascades does not have a general solution up to the present time. The proposed approach supports secondary flow analysis whenever exit streamwise vorticity produced by inlet endwall boundary layers is of interest. The idea is to compute the reference flow by applying slip boundary conditions at the endwalls in a viscous 3D numerical simulation, in which uniform total pressure is prescribed at the inlet. Thus the reference flow keeps the 3D nature of the actual flow except for the contribution of the endwall boundary layer vorticity. The resulting secondary field is then derived by projecting the 3D flow field (obtained from both an experiment and a fully viscous simulation) along the local reference flow direction; this approach can be proficiently applied to any complex geometry. This method allows the representation of secondary velocity vectors with a better estimation of the vortex extension, since it offers the opportunity to visualize also the region of the vortices, which can be approximated as a potential type. Furthermore, a proficient evaluation of the secondary vorticity and deviation angle effectively induced by the annulus boundary layer is possible. The approach was preliminarily verified against experimental data in linear cascades characterized by cylindrical blades, not reported for the sake of brevity, showing a very good agreement with the standard methodology based only on the experimental midspan flow field. This article presents secondary flows obtained by the application of the proposed methodology on two annular cascades with cylindrical and 3D-designed blades, stressing the differences with other definitions. Both numerical and experimental results are considered.

Vorticity transport in a corner formed by a solid wall and a free surface

2002 ◽  
Vol 465 ◽  
pp. 331-352 ◽  
Author(s):  
L. M. GREGA ◽  
T. Y. HSU ◽  
T. WEI
Keyword(s):  
Boundary Layer ◽  
Free Surface ◽  
Secondary Flow ◽  
Mixed Boundary ◽  
Solid Wall ◽  
Secondary Flows ◽  
Exact Nature ◽  
Streamwise Vorticity ◽  
The Cross ◽  
Vorticity Transport

There is a growing body of literature in which turbulent boundary layer flow along a mixed-boundary corner formed by a vertical solid wall and a horizontal free surface has been examined. While there is consensus regarding the existence of weak secondary flows in the near corner region, there is some disagreement as to the exact nature and origin of these flows. In two earlier works by the authors, evidence was presented supporting the existence of a weak streamwise vortex which rotates in toward the wall at the free surface and down away from the surface along the wall. This ‘inner secondary vortex’ is accompanied by an ‘outer secondary flow’ which transports low-momentum boundary layer fluid up along the wall and outward at the free surface. The magnitudes of the cross-stream velocities associated with these secondary flows were measured to be on the order of 1% of the free-stream speed. In this paper, high-resolution DPIV measurements made in the cross-stream plane are presented. These clearly show the inner and outer secondary flows. The cross-stream vector fields allow computation of terms in the turbulent streamwise vorticity transport equation. These terms indicate mean vorticity transport at the free surface associated with the outer secondary flow. In addition there appears to be a balance between the wall-normal and free-surface-normal fluctuating vorticity reorientation terms.

Interaction Between Inlet Boundary Layer, Tip-Leakage and Secondary Flows in a Low-Speed Turbine Cascade

1994 ◽  
Author(s):  
J. K. K. Chan ◽  
M. I. Yaras ◽  
S. A. Sjolander
Keyword(s):  
Boundary Layer ◽  
Secondary Flow ◽  
Large Scale ◽  
Field Measurements ◽  
Secondary Flows ◽  
Tip Clearance ◽  
Turbine Cascade ◽  
Streamwise Vorticity ◽  
Tip Leakage Flow ◽  
Tip Leakage

An experiment has been conducted in a large-scale linear turbine cascade to examine the interaction between the inlet endwall boundary layer, tip-leakage and secondary flows. Detailed flow field measurements have been made upstream and downstream of the blade row for two values of inlet boundary layer thickness (δ*/c of about 0.015 and 0.04) together with three values of tip clearance (gap heights of 0.0, 1.5 and 5.5 percent of blade chord). In the downstream plane, the total pressure deficits associated with the tip-leakage and secondary flows were discriminated by examining the sign of the streamwise vorticity. For this case, the streamwise vorticity of the two flows have opposite signs and this proved an effective criterion for separating the flows despite their close proximity in space. It was found that with clearance the loss associated with the secondary flow was substantially reduced from the zero clearance value, in contradiction to the assumption made in most loss prediction schemes. Further work is needed, notably to clarify the influence of relative tip-wall motion which in turbines reduces the tip-leakage flow while enhancing the secondary flow.

Numerical and experimental study of mechanisms responsible for turbulent secondary flows in boundary layer flows over spanwise heterogeneous roughness

2015 ◽  
Vol 768 ◽  
pp. 316-347 ◽  
Author(s):  
William Anderson ◽  
Julio M. Barros ◽  
Kenneth T. Christensen ◽  
Ankit Awasthi
Keyword(s):  
Boundary Layer ◽  
Kinetic Energy ◽  
Secondary Flow ◽  
Turbulent Kinetic Energy ◽  
Secondary Flows ◽  
Streamwise Vorticity ◽  
Reynolds Stresses ◽  
Spatial Gradients ◽  
Normal Mean ◽  
Layer Flow

We study the dynamics of turbulent boundary layer flow over a heterogeneous topography composed of roughness patches exhibiting relatively high and low correlation in the streamwise and spanwise directions, respectively (i.e. the roughness appears as streamwise-aligned ‘strips’). It has been reported that such roughness induces a spanwise-wall normal mean secondary flow in the form of mean streamwise vorticity associated with counter-rotating boundary-layer-scale circulations. Here, we demonstrate that this mean secondary flow is Prandtl’s secondary flow of the second kind, both driven and sustained by spatial gradients in the Reynolds-stress components, which cause a subsequent imbalance between production and dissipation of turbulent kinetic energy that necessitates secondary advective velocities. In reaching this conclusion, we study (i) secondary circulations due to spatial gradients of turbulent kinetic energy, and (ii) the production budgets of mean streamwise vorticity by gradients of the Reynolds stresses. We attribute the secondary flow phenomena to extreme peaks of surface stress on the relatively high-roughness regions and associated elevated turbulence production in the fluid immediately above. An optimized state is attained by entrainment of fluid exhibiting the lowest turbulent stresses – from above – and subsequent lateral ejection in order to preserve conservation of mass.

scholarly journals Endwall Loss in Turbine Cascades

2017 ◽  
Vol 139 (8) ◽  
Author(s):  
John D. Coull
Keyword(s):  
Boundary Layer ◽  
Secondary Flow ◽  
Turbine Blades ◽  
Secondary Flows ◽  
Navier Stokes ◽  
Design Parameters ◽  
Streamwise Vorticity ◽  
Suction Surface ◽  
Blade Thickness ◽  
The Impact

Prior to the detailed design of components, turbomachinery engineers must guide a mean-line or throughflow design toward an optimum configuration. This process requires a combination of informed judgement and low-order correlations for the principle sources of loss. With these requirements in mind, this paper examines the impact of key design parameters on endwall loss in turbines, a problem which remains poorly understood. This paper presents a parametric study of linear cascades, which represent a simplified model of real-engine flow. The designs are nominally representative of the low-pressure turbine blades of an aero-engine, with varying flow angles, blade thickness, and suction surface lift styles. Reynolds-averaged Navier–Stokes (RANS) calculations are performed for a single aspect ratio (AR) and constant inlet boundary layer thickness. To characterize the cascades studied, the two-dimensional design space is examined before studying endwall losses in detail. It is demonstrated that endwall loss can be decomposed into two components: one due to the dissipation associated with the endwall boundary layer and another induced by the secondary flows. This secondary-flow-induced loss is found to scale with a measure of streamwise vorticity predicted by classical secondary flow theory.

Effects of Inlet Distortion on the Flow Field in a Transonic Compressor Rotor

1996 ◽  
Author(s):  
Chunill Hah ◽  
Douglas C. Rabe ◽  
Thomas J. Sullivan ◽  
Aspi R. Wadia
Keyword(s):  
Boundary Layer ◽  
Flow Field ◽  
Viscous Flow ◽  
Total Pressure ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Aerodynamic Loss ◽  
Transonic Compressor ◽  
Inlet Distortion ◽  
Compressor Rotor

The effects of circumferential distortions in inlet total pressure on the flow field in a low-aspect-ratio, high-speed, high-pressure-ratio, transonic compressor rotor are investigated in this paper. The flow field was studied experimentally and numerically with and without inlet total pressure distortion. Total pressure distortion was created by screens mounted upstream from the rotor inlet. Circumferential distortions of 8 periods per revolution were investigated at two different rotor speeds. The unsteady blade surface pressures were measured with miniature pressure transducers mounted in the blade. The flow fields with and without inlet total pressure distortion were analyzed numerically by solving steady and unsteady forms of the Reynolds-averaged Navier-Stokes equations. Steady three-dimensional viscous flow calculations were performed for the flow without inlet distortion while unsteady three-dimensional viscous flow calculations were used for the flow with inlet distortion. For the time-accurate calculation, circumferential and radial variations of the inlet total pressure were used as a time-dependent inflow boundary condition. A second-order implicit scheme was used for the time integration. The experimental measurements and the numerical analysis are highly complementary for this study because of the extreme complexity of the flow field. The current investigation shows that inlet flow distortions travel through the rotor blade passage and are convected into the following stator. At a high rotor speed where the flow is transonic, the passage shock was found to oscillate by as much as 20% of the blade chord, and very strong interactions between the unsteady passage shock and the blade boundary layer were observed. This interaction increases the effective blockage of the passage, resulting in an increased aerodynamic loss and a reduced stall margin. The strong interaction between the passage shock and the blade boundary layer increases the peak aerodynamic loss by about one percent.

Second Vane Total Pressure Loss Due to Endwall Iceform Contouring

2008 ◽  
Author(s):  
Ronald S. LaFleur
Keyword(s):  
Heat Transfer ◽  
Secondary Flow ◽  
Pressure Loss ◽  
Total Pressure ◽  
Aerodynamic Drag ◽  
Pressure Coefficient ◽  
Secondary Flows ◽  
Total Pressure Loss ◽  
Surface Shape ◽  
Exit Plane

The iceformation design method generates an endwall contour, altering the secondary flows that produce elevated endwall heat transfer load and total pressure losses. Iceformation is an analog to regions of metal melting where a hot fluid alters the isothermal surface shape of a part as it is maintained by a cooling fluid. The passage flow, heat transfer and geometry evolve together under the constraints of flow and thermal boundary conditions. The iceformation concept is not media dependent and can be used in analogous flows and materials to evolve novel boundary shapes. In the past, this method has been shown to reduce aerodynamic drag and total pressure loss in flows such as diffusers and cylinder/endwall junctures. A prior paper [1] showed that the Reynolds number matched iceform geometry had a 24% lower average endwall heat transfer than the rotationally symmetric endwall geometry of the Energy Efficiency Engine (E3). Comparisons were made between three endwall geometries: the ‘iceform’, the ‘E3’ and the ‘flat’ as a limiting case of the endwall design space. This paper adds to the iceformation design record by reporting the endwall aerodynamic performances. Second vane exit flow velocities and pressures were measured using an automated 2-D traverse of a 1.2 mm diameter five-hole probe. Exit plane maps for the three endwall geometries are presented showing the details of the total pressure coefficient contours and the velocity vectors. The formation of secondary flow vortices is shown in the exit plane and this results in an impact on exit plane total pressure loss distribution, off-design over- and under-turning of the exit flow. The exit plane contours are integrated to form overall measures of the total pressure loss. Relative to the E3 endwall, the iceform endwall has a slightly higher total pressure loss attributed to higher dissipation of the secondary flow within the passage. The iceform endwall has a closer-to-design exit flow pattern than the E3 endwall.

scholarly journals Numerical and Experimental Analysis of Secondary Flow in Modern State-of-the-Art Low Pressure Guide Vane Rows

1995 ◽  
Author(s):  
Ernst Lindner
Keyword(s):  
Aspect Ratio ◽  
Secondary Flow ◽  
Total Pressure ◽  
Guide Vane ◽  
Numerical Results ◽  
Flow Behaviour ◽  
Inlet Guide Vane ◽  
Streamwise Vorticity ◽  
Pressure Losses ◽  
Turbine Guide Vane

To enhance the performance of the inlet guide vane and the annular duct of a jet engine, a detailed investigation of annular cascades with two different types of turbine guide vane rows is made. The first one is a leaned guide vane with an aspect ratio of two and a half and a transition duct ahead of the vane. To avoid the losses associated to the decelerating transition duct an alternative vane is designed and investigated with the same inlet and exit conditions. In this case the chord of the vane is increased to the effect that the vane begins immediately at the enterance of the diverging annulus and so a continuously accelerated flow is achieved. To maintain a good performance for this configuration a bowed-type vane with an aspect ratio of one is designed. The aim of the investigation is to obtain detailed informations on the secondary flow behaviour with particular regard to the development of the total pressure losses and the streamwise vorticity of the vortices inside and behind the blade rows. In the first step a three-dimensional, structured, explicit finite-volume flow-solver with a k–ε turbulence model is validated against the measurements, which were made in cross-sections behind the blades. Having proved that the numerical results are very close to the experimental ones, the secondary flow behaviour inside and behind the blade rows is analysed in the second step. By calculating the streamwise vorticity from the numerical results the formation of horse-shoe vortex, passage-vortex and the trailing edge vortex shed is investigated. The differences of the vortical motion and the formation of the total pressure losses between the two configurations of turbine guide vane rows are discussed.

scholarly journals LES and RANS Analysis of the End-Wall Flow in a Linear LPT Cascade: Part I — Flow and Secondary Vorticity Fields Under Varying Inlet Condition

2018 ◽  
Author(s):  
R. Pichler ◽  
Yaomin Zhao ◽  
R. D. Sandberg ◽  
V. Michelassi ◽  
R. Pacciani ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Secondary Flow ◽  
Flow Characteristics ◽  
Flow Region ◽  
Secondary Flows ◽  
Wall Boundary Layer ◽  
Wall Boundary ◽  
Wall Flow ◽  
End Wall ◽  
The Impact

In low-pressure-turbines (LPT) around 60–70% of losses are generated away from end-walls, while the remaining 30–40% is controlled by the interaction of the blade profile with the end-wall boundary layer. Experimental and numerical studies have shown how the strength and penetration of the secondary flow depends on the characteristics of the incoming end-wall boundary layer. Experimental techniques did shed light on the mechanism that controls the growth of the secondary vortices, and scale-resolving CFD allowed to dive deep into the details of the vorticity generation. Along these lines, this paper discusses the end-wall flow characteristics of the T106 LPT profile at Re = 120K and M = 0.59 by benchmarking with experiments and investigating the impact of the incoming boundary layer state. The simulations are carried out with proven Reynolds-averaged Navier–Stokes (RANS) and large-eddy simulation (LES) solvers to determine if Reynolds Averaged models can capture the relevant flow details with enough accuracy to drive the design of this flow region. Part I of the paper focuses on the critical grid needs to ensure accurate LES, and on the analysis of the overall time averaged flow field and comparison between RANS, LES and measurements when available. In particular, the growth of secondary flow features, the trace and strength of the secondary vortex system, its impact on the blade load variation along the span and end-wall flow visualizations are analysed. The ability of LES and RANS to accurately predict the secondary flows is discussed together with the implications this has on design.

Aerodynamic Performance Evaluation of Axial Flow Fan Using Numerical Techniques

2021 ◽  
Author(s):  
Raghuvaran D. ◽  
Satvik Shenoy ◽  
Srinivas G
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Rotational Speed ◽  
Total Pressure ◽  
Axial Flow ◽  
High Mass ◽  
Ansys Fluent ◽  
Industrial Sectors ◽  
Mass Flow Rates

Abstract Axial flow fans (AFF) are extensively used in various industrial sectors, usually with flows of low resistance and high mass flow rates. The blades, the hub and the shroud are the three major parts of an AFF. Various kinds of optimisation can be implemented to improve the performance of an AFF. The most common type is found to be geometric optimisation including variation in number of blades, modification in hub and shroud radius, change in angle of attack and blade twist, etc. After validation of simulation model and carrying out a grid independence test, parametric analysis was done on an 11-bladed AFF with a shroud of uniform radius using ANSYS Fluent. The rotational speed of the fan and the velocity at fan inlet were the primary variables of the study. The variation in outlet mass flow rate and total pressure was studied for both compressible and incompressible ambient flows. Relation of mass flow rate and total pressure with inlet velocity is observed to be linear and exponential respectively. On the other hand, mass flow rate and total pressure have nearly linear relationship with rotational speed. A comparison of several different axial flow tracks with the baseline case fills one of the research gaps.

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