Effects of Core Flow Swirl on the Flow Characteristics of a Scalloped Forced Mixer

2012 ◽  
Vol 134 (11) ◽  
Author(s):  
Zhijun Lei ◽  
Ali Mahallati ◽  
Mark Cunningham ◽  
Patrick Germain
Keyword(s):  
Pressure Ratio ◽  
Velocity Ratio ◽  
Flow Characteristics ◽  
Equivalent Diameter ◽  
Streamwise Vortices ◽  
Core Flow ◽  
The Core ◽  
Flow Swirl ◽  
Swirl Angle ◽  
And Performance

This paper presents a detailed experimental investigation of the influence of core flow swirl on the mixing and performance of a scaled turbofan mixer with 12 scalloped lobes. Measurements were made downstream of the mixer in a coaxial wind tunnel. The core-to-bypass velocity ratio was set to 2:1, temperature ratio to 1.0, and pressure ratio to 1.03, giving a Reynolds number of 5.2 × 105, based on the core flow velocity and equivalent diameter. In the core flow, the background turbulence intensity was raised to 5% and the swirl angle was varied from 0 deg to 30 deg with five vane geometries. At low swirl angles, additional streamwise vortices were generated by the deformation of normal vortices due to the scalloped lobes. With increased core swirl, greater than 10 deg, the additional streamwise vortices were generated mainly due to radial velocity deflection, rather than stretching and deformation of normal vortices. At high swirl angles, stronger streamwise vortices and rapid interaction between various vortices promoted downstream mixing. Mixing was enhanced with minimal pressure and thrust losses for the inlet swirl angles less than 10 deg. However, the reversed flow downstream of the center body was a dominant contributor to the loss of thrust at the maximum core flow swirl angle of 30 deg.

Effects of Core Flow Swirl on the Flow Characteristics of a Scalloped Forced Mixer

2011 ◽  
Author(s):  
Zhijun Lei ◽  
Ali Mahallati ◽  
Mark Cunningham ◽  
Patrick Germain
Keyword(s):  
Pressure Ratio ◽  
Velocity Ratio ◽  
Flow Characteristics ◽  
Pressure Probe ◽  
Streamwise Vortices ◽  
Core Flow ◽  
The Core ◽  
Flow Swirl ◽  
Swirl Angle ◽  
Oil Flow

This paper presents a detailed experimental investigation of the influence of core flow swirl on the mixing and performance of a scaled turbofan mixer with 12 scalloped lobes. Measurements were made downstream of the mixer in a co-annular wind tunnel. The core-to-bypass velocity ratio was set to 2:1, temperature ratio to 1.0, and pressure ratio to 1.03, giving a Reynolds number of 5.2 × 105, based on the core flow velocity and equivalent hydraulic diameter. In the core flow, the background turbulence intensity was raised to 5% and the swirl angle was varied using five vane geometries from 0° to 30°. Seven-hole pressure probe measurements and surface oil flow visualization were used to describe the flowfield and the mixer performance. At low swirl angles, additional streamwise vortices were generated by the deformation of normal vortices due to the scalloped lobes. With increased core swirl, greater than 10°, the additional streamwise vortices were generated mainly due to radial velocity deflection, rather than stretching and deformation of normal vortices. At high swirl angles, stronger streamwise vortices and rapid interaction between various vortices promoted downstream mixing. Mixing was enhanced with minimal or no total pressure and thrust losses for the inlet swirl angles less than 10°. However, the reversed flow downstream of the center-body was a dominant contributor to the loss of thrust at the maximum core flow swirl angle of 30°.

Flow Characteristics of Double Serpentine Convergent Nozzle With Different Inlet Configuration

2018 ◽  
Vol 140 (8) ◽  
Author(s):  
Sun Xiao-Lin ◽  
Wang Zhan-Xue ◽  
Zhou Li ◽  
Shi Jing-Wei ◽  
Cheng Wen
Keyword(s):  
Flow Characteristics ◽  
Complex Flow ◽  
Convergent Nozzle ◽  
Core Flow ◽  
The Core ◽  
Setting Angle ◽  
Swirl Angle ◽  
Swirl Flows ◽  
Flow Features ◽  
Inlet Swirl

Serpentine nozzles have been used in stealth fighters to increase their survivability. For real turbofan aero-engines, the existence of the double ducts (bypass and core flow), the tail cone, the struts, the lobed mixers, and the swirl flows from the engine turbine, could lead to complex flow features of serpentine nozzle. The aim of this paper is to ascertain the effect of different inlet configurations on the flow characteristics of a double serpentine convergent nozzle. The detailed flow features of the double serpentine convergent nozzle including/excluding the tail cone and the struts are investigated. The effects of inlet swirl angles and strut setting angles on the flow field and performance of the serpentine nozzle are also computed. The results show that the vortices, which inherently exist at the corners, are not affected by the existence of the bypass, the tail cone, and the struts. The existence of the tail cone and the struts leads to differences in the high-vorticity regions of the core flow. The static temperature contours are dependent on the distributions of the x-streamwise vorticity around the core flow. The high static temperature region is decreased with the increase of the inlet swirl angle and the setting angle of the struts. The performance loss of the serpentine nozzle is mostly caused by its inherent losses such as the friction loss and the shock loss. The performance of the serpentine nozzle is decreased as the inlet swirl angle and the setting angle of the struts increase.

Experimental Investigation of the Effects of Nozzle Length on the Performance of Low Mach Number Air-Air Ejector With Entraining Diffuser

2013 ◽  
Author(s):  
A. Namet-Allah ◽  
A. M. Birk
Keyword(s):  
Nozzle Exit ◽  
Back Pressure ◽  
Flow Rates ◽  
Core Flow ◽  
The Core ◽  
Flow Swirl ◽  
Swirl Angle ◽  
Mass Flow Rates ◽  
Nozzle Inlet ◽  
Center Body

The core flow separation in air-air ejectors is significantly affected by the length of the exhaust nozzle. This length was changed by moving the annulus’ center body end 4, 7, and 12 cm upstream and 1 cm downstream of the nozzle inlet. The velocity profiles at the nozzle exit were measured at different mass flow rates and at 10, 20 and 30 degree swirl angles. These measurements were also conducted at two annulus’ center body end positions with elliptical and square shapes, 12 and 7 cm upstream of the nozzle inlet, using two nozzle exit diameters. At 4, 7, and 12 cm upstream and 1 cm downstream of the nozzle inlet, the ejector performance was also measured at ambient temperature and at different flow swirl angles. It was found that the square shape of the annulus’ center body decreased the size of the core flow separation behind the annulus center body compared with the elliptical shape by improving the flatness of the flow velocity at the nozzle exit under different mass flow rates, swirl angles, positions of the annulus’ center body, and nozzle exit diameters. It was seen that moving the end of the annular center body upstream has considerable effects on the size and nature of the core separation behind the annulus’ center body and consequently on the ejector performance. At a zero swirl angle, the ejector pumping ratio slightly increased, decreased, and then increased again by moving the annulus’ center body from 12 cm to 7 cm upstream, from 7 cm to 4 cm upstream, and from 4 cm upstream to 1 cm downstream of the nozzle inlet respectively. These changes in the annulus’ center body position caused the back pressure coefficient to decrease, increase, and then increase again. The same trend in pumping ratio and back pressure was observed for both 10 and 20 degree flow swirl angle conditions when the annulus’ center body was moved as described.

Influence of Inlet Swirl on the Aerodynamics of a Model Turbofan Lobed Mixer

2010 ◽  
Author(s):  
Zhijun Lei ◽  
Ali Mahallati ◽  
Mark Cunningham ◽  
Patrick Germain
Keyword(s):  
Swirling Flow ◽  
Velocity Ratio ◽  
Core Region ◽  
Streamwise Vortices ◽  
Reversed Flow ◽  
Flow Measurements ◽  
Core Flow ◽  
The Core ◽  
Exit Nozzle ◽  
Inlet Swirl

This paper presents a detailed experimental investigation of the influence of core flow inlet swirl on the mixing and performance of a 12-lobe un-scalloped turbofan mixer. Measurements were made downstream of the mixer in a co-annular wind tunnel. The core-to-bypass velocity ratio was set to 2:1, temperature ratio to 1.0, and pressure ratio to 1.03, giving a Reynolds number of 5.2×105, based on the core flow inlet velocity and equivalent hydraulic diameter. In the core flow, the background turbulence intensity was raised to 5% and the swirl angle was varied using five vane geometries, with nominally uniform swirl angles of 0°, 5°, 10°, 20° and 30°. Flow measurements captured flow structures involved in the mixing process. Most of mixing took place immediately downstream of the exit nozzle. The vane wake slightly enhanced large scale mixing of streamwise vortices. At low swirl angles, mixing was found to be mainly due to the interaction between streamwise vortices and normal vortices. At high swirl angles, the lobed mixer acted similar to a guide vane and removed most of the inlet swirl between the crest and trough of the mixer. However, the upstream swirling flow persisted in the core region between the center-body and lobed mixer trough, causing a reverse flow zone downstream of the centre-body. As the reversed flow became larger with increasing swirl, the swirling flow in the core region moved radially outwards and further interacted with the outer region flow. The stronger interaction of streamwise vortices with normal vortex improved mixing from the trough to the crest of the lobed mixer. The balance between enhanced mixing and increased reversed flow downstream of the centre-body, resulted in increased overall total pressure losses with increasing inlet swirl angles.

Characterisation of Static Strip Seal Flow

2007 ◽  
Author(s):  
Arash Farahani ◽  
Peter Childs
Keyword(s):  
Gas Flow ◽  
Pressure Ratio ◽  
Flow Characteristics ◽  
Main Stream ◽  
Cfd Modelling ◽  
Height Range ◽  
And Performance ◽  
Nozzle Guide ◽  
The Cost ◽  
Cooling Air

Strip seals are used in gas turbine engines between two static elements or between components which do not move relative to each other, such as Nozzle Guide Vanes (NGVs). The key role of a strip seal between NGV segments is sealing between the flow through the main stream annulus and the internal air system, a further purpose is to limit the inter-segmental movements. In general the shape of the strip seal is a rectangular strip that fits into two slots in adjacent components. The minimum clearance required for static strip seals must be found by accounting for thermal expansion, misalignment, and application, to allow correct fitment of the strip seals. Any increase in leakage raises the cost due to an increase in the cooling air use, which is linked to specific fuel consumption, and it can also alter gas flow paths and performance. The narrow path within the seal assembly, especially the height has the most significant affect on leakage. The height range of the narrow path studied in this paper is 0.01–0.06 mm. The behaviour of the flow passing through the narrow path has been studied using CFD modelling and measurements in a bespoke rig. The CFD and experimental results show that normalized leakage flow increases with pressure ratio before reaching a maximum. The main aim of this paper is to provide new experimental data to verify the CFD modelling for static strip seals. The typical flow characteristics validated by CFD modelling and experiments can be used to predict the flow behaviour for future static strip seal designs.

scholarly journals Performance and Exit Flow Characteristics of Mixed-Flow Turbines

1997 ◽  
Vol 3 (4) ◽  
pp. 277-293 ◽  
Author(s):  
C. Arcoumanis ◽  
R. F. Martinez-Botas ◽  
J. M. Nouri ◽  
C. C. Su
Keyword(s):  
Steady State ◽  
Velocity Ratio ◽  
Tangential Velocity ◽  
Flow Characteristics ◽  
Mixed Flow ◽  
Cross Sectional ◽  
Flow Angle ◽  
Turbine Efficiency ◽  
And Performance ◽  
Inlet Angle

The performance and exit flow characteristics of two mixed-flow turbines have been investigated under steady-state conditions. The two rotors differ mainly in their inlet angle geometry, one has a nominal constant incidence (rotor B) and the other has a constant blade angle (rotor C), but also in the number of blades. The results showed that the overall peak efficiency of rotor C is higher than that of rotor B. Two different volutes were also used for the tests, differing in their cross-sectional area, which confirm that the new larger area volute turbine has a higher efficiency than the old one, particularly at lower speeds, and a fairly uniform variation with velocity ratio.The flow exiting the blades has been quantified by laser Doppler velocimetry. A difference in the exit flow velocity for rotors B and C with the new volute was observed which is expected given their variation in geometry and performance. The tangential velocities near the shroud resemble a forced vortex flow structure, while a uniform tangential velocity component was measured near the hub. The exit flow angles for both rotor cases decreased rapidly from the shroud to a minimum value in the annular core region before increasing gradually towards the hub. In addition, the exit flow angles with both rotors were reduced with increasing rotational speeds. The magnitude of the absolute flow angle was reduced in the case of rotor C, which may explain the improved steady state performance with this rotor. The results also revealed a correlation between the exit flow angle and the performance of the turbines; a reduction in flow angle resulted in an increase in the overall turbine efficiency.

Analysis of Flow Migration in an Ultra-Compact Combustor

2011 ◽  
Author(s):  
Brian T. Bohan ◽  
Marc D. Polanka
Keyword(s):  
Ambient Pressure ◽  
Flow Characteristics ◽  
Turbine Rotor ◽  
Secondary Flows ◽  
Realistic Condition ◽  
Core Flow ◽  
Mixing Properties ◽  
The Core ◽  
Computational Fluid Dynamics Cfd ◽  
Outside Diameter

The Ultra Compact Combustor (UCC) has the potential to offer improved thrust-to-weight and overall efficiency in a turbojet engine. The thrust-to-weight improvement is due to a reduction in engine weight by shortening the combustor section through the use of the revolutionary UCC design. The improved efficiency is achieved by using an increased fuel-to-air mass ratio, and allowing the fuel to fully combust prior to exiting the UCC system. Furthermore, g-loaded combustion offers increased flame speeds that can lead to smaller combustion volumes. The circumferential combustion of the fuel in the UCC cavity results in hot gases present at the outside diameter of the core flow. This orientation creates an issue in that the flow from the circumferential cavity needs to migrate radially and blend with the core flow to present a uniform temperature distribution to the high-pressure turbine rotor. A computational fluid dynamics (CFD) analysis is presented for the flow patterns in the combustor section of a representative fighter-scale engine. The analysis included a study of secondary flows, cavity flow characteristics, shear layer interactions and mixing properties. An initial understanding of primary factors that impact the radial migration is presented. Computational comparisons were also made between an engine realistic condition and an ambient pressure rig environment.

Flow-induced vibration and noise in control valve

2015 ◽  
Vol 229 (18) ◽  
pp. 3368-3377 ◽  
Author(s):  
Li-fei Zeng ◽  
Guan-wei Liu ◽  
Jing-ru Mao ◽  
Shun-sen Wang ◽  
Qi Yuan ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Flow Pattern ◽  
Annular Flow ◽  
Pressure Ratio ◽  
Pressure Fluctuations ◽  
Control Valve ◽  
Steam Turbines ◽  
Core Flow ◽  
Control Valves ◽  
The Core

Control valves are used as flow regulators for steam turbines, which operate under wide ranges of valve openings and pressure ratios. The inherent throttling action and complex 3D flow in control valves result in vibration and intolerable noise at small and medium valve openings. The vibration and noise clearly are firmly with the flow pattern. Experiments and numerical simulation are the primary means of determining the mechanisms. In this paper, a phenomenon of sound mutation in control valve was experimentally observed by continuously changing the pressure ratio. This phenomenon is explained for the first time. Different noise and pressure fluctuations can appear even under the same condition, depending on the process of changing the pressure ratio. A method of continuously changing the pressure ratio was used in the unsteady numerical simulation to reveal the mechanism. The results show that sound mutation occurs due to the change of annular flow and core flow. The annular flow has a lower noise and a more stable flow pattern than the core flow. Sound mutation can be used as a simple way of determining the ranges of the core flow and the annular flow.

Effects of Scalloping on the Mixing Mechanisms of Forced Mixers With Highly Swirling Core Flow

2013 ◽  
Vol 135 (7) ◽  
Author(s):  
Alex Wright ◽  
Zhijun Lei ◽  
Ali Mahallati ◽  
Mark Cunningham ◽  
Julio Militzer
Keyword(s):  
Separation Bubble ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Suction Surface ◽  
Mixing Rate ◽  
Reduced Pressure ◽  
Core Flow ◽  
Flow Swirl ◽  
Swirl Angle ◽  
Mixing Rates

This paper presents a detailed experimental and computational investigation of the effects of scalloping on the mixing mechanisms of a scaled 12-lobe turbofan mixer. Scalloping was achieved by eliminating approximately 70% of the lobe sidewall area. Measurements were made downstream of the mixer in a co-annular wind tunnel, and the simulations were carried out using an unstructured Reynolds averaged Navier–Stokes (RANS) solver, Numeca FINE/Hexa, with k-ω SST model. In the core flow, the swirl angle was varied from 0 deg to 30 deg. At high swirl angles, a three-dimensional separation bubble was formed on the lobe's suction surface penetration region and resulted in the generation of a vortex at the lobe valley. The valley vortex quickly dissipated downstream. The mixer lobes removed most of the swirl, but scalloped lobes removed less swirl in the region of the scalloped notch. The residual swirl downstream of the scalloped mixer interacted with the vortices and improved mixing rates compared to the unscalloped mixer. Core flow swirl up to 10 deg provided improved mixing rates and reduced pressure and thrust losses for both mixers. As core flow swirl increased beyond 10 deg, the mixing rate continued to improve, but pressure and thrust losses declined compared to the zero swirl case. Lobe scalloping, in high swirl conditions, resulted in better mixing and improved pressure loss over the unscalloped mixer but at the expense of reduced thrust.

Inlet and Exit Flow Characteristics of Mixed Flow Turbines

1998 ◽  
Author(s):  
C. Arcoumanis ◽  
R. F. Martinez-Botas ◽  
J. M. Nouri ◽  
C. C. Su
Keyword(s):  
Incidence Angle ◽  
Pressure Ratio ◽  
Flow Characteristics ◽  
Expansion Ratio ◽  
Superior Performance ◽  
Mixed Flow ◽  
Flow Angle ◽  
High Pressure Ratio ◽  
Swirl Angle ◽  
Design Speed

The steady performance of mainly two high pressure ratio mixed flow turbines for an automotive turbocharger (expansion ratio of 2.9) has been investigated and the results indicated superior performance of the rotor with a constant inlet blade angle relative to that with a nominally constant incidence angle. These results have been confirmed by the measurement of the three components of velocity, the Reynolds normal stresses and the flow angle at the inlet and exit of the mixed-flow turbine rotors by laser Doppler velocimetry (LDV) under steady state conditions. The turbine testing conditions corresponded to the 50% and 70% design speeds, equivalent to 29,400 and 41,300 rpm respectively. The velocity results have indicated that the flow upstream of the rotor varies significantly along the blade inlet plane, and this is more evident at the 50% design speed. The flow in the volute behaves as a free vortex except in regions close to the hub, while the exit flow revealed that the constant incidence design rotor has a significantly higher exit swirl angle than the constant blade design, in agreement with the higher exit kinetic energy loss in the former case.

Sign in / Sign up

Export Citation Format

Share Document