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.

Experimental Study: Effects of the Annulus’ Center Body End Shape on the Performance of Low Mach Number Air-Air Ejector With Entraining Diffuser

2013 ◽  
Author(s):  
A. Namet-Allah ◽  
A. M. Birk
Keyword(s):  
Reynolds Number ◽  
Mach Number ◽  
Nozzle Exit ◽  
Pressure Coefficient ◽  
Back Pressure ◽  
Low Mach Number ◽  
The Core ◽  
Swirl Angle ◽  
Air Ejector ◽  
Center Body

In the present paper, an experimental investigation of the performance of a low mach number round straight air-air ejector with a 4-ring entraining diffuser is reported. The ejector system was mounted on an annular flow wind tunnel. Based on the hydraulic diameter and average velocity and temperature at the nozzle exit, the tunnel provides cold flow at Mach 0.2 with a Reynolds number of 5.2×105 and hot flow at Mach 0.27 with a Reynolds number of 2.6×105. The end shape of the annulus’ center body has major effects on the core separation size and shape that strongly affects the ejector performance. The effects of the annulus’ center body with elliptical and square ends on the ejector pumping, wall static pressure distribution and back pressure were investigated under different flow temperatures and swirl angles: 0°, 10°, 20°, and 30°. These measurements were conducted at 129 mm standoff distance using two different nozzle exit diameters. It was found that for both nozzle exit diameters, using the annulus’ center body with a square end improved the total pumping ratio over its ratio with an elliptical end due to the flatness of the core separation at the nozzle exits. For all configurations tested, the maximum entrainment ratio was observed with 20° swirl angle and the back pressure coefficient decreased as swirl angle increased. Removing the elliptical end, creating the square shape, the flow has more space to spread after the annulus’ center body to give the higher centerline velocity which enhances the flow uniformity at the nozzle and diffuser exits.

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°.

Characterizing the Effect of Radial Vane Height on Flame Migration in an Ultra Compact Combustor

2011 ◽  
Author(s):  
Kenneth D. LeBay ◽  
Marc D. Polanka ◽  
Richard D. Branam
Keyword(s):  
Flow Velocity ◽  
Mass Flow ◽  
Temperature Profiles ◽  
Core Mass ◽  
Freestream Velocity ◽  
Flow Rates ◽  
Core Flow ◽  
Injection Angle ◽  
The Core ◽  
Mass Flow Rates

The Ultra Compact Combustor (UCC) has shown viable merit for significantly improving gas turbine combustor performance. UCC models for small engines can provide centrifugal loading up to 4,000 gs. However, as the scale of the combustor increases, the g-load will necessarily decrease and the radial vane height will increase. Thus, the importance of understanding flame migration over increasing radial vane heights is pivotal to the applicability of this design to larger engine diameters. The Air Force Institute of Technology’s Combustion Optimization and Analysis Laser laboratory studied this effect with a sectional UCC model using three different vane heights. By varying the mass flow rates of the circumferential UCC section, the g-loading was varied from 500–2,000 gs. Two-line Planar Laser Induced Fluorescence at 10Hz was used for 2D temperature profiles. High-speed video at 2kHz was also used for qualitative flame migration characterization. Several cases were studied varying the radial vane height, the circumferential g-load, and the UCC/core mass flow ratio but specifically focusing on the interaction between matching the core mass flow and the core freestream velocity among the different vane heights. Finally, the decreased core flow velocity for the same mass flow weakened the shear layer between the main and cavity flows and this allowed deeper flame migration into the core flow from the UCC. Control of the overall flame migration is the key to produce desirable combustor exit temperature profiles. Increased spans lead to higher velocity gradients and increased flame injection angles at the same mass flow rates. However, at the same core flow velocities and UCC to core flow velocity ratios the flame injection angle was relatively independent of the radial vane height and almost entirely dependent on the core flow velocity alone.

Performance of a Round Ejector With 22.5° Bent Entraining Diffuser

2010 ◽  
Author(s):  
Qi Chen ◽  
A. M. Birk
Keyword(s):  
Outer Side ◽  
Similar Data ◽  
Flow Temperature ◽  
Flow Rates ◽  
Hot Gas ◽  
Flow Swirl ◽  
Swirl Angle ◽  
Mass Flow Rates ◽  
Core Cooling ◽  
Velocity Pressure

This paper presents experimental data for the performance of a round ejector with a 22.5° bent entraining diffuser. The experiments were carried out on a hot gas wind tunnel that could provide primary mass flow rates up to 2.2 kg/s at ambient temperature and 1.8 kg/s at 500°C. Velocity, pressure and temperature were measured in the annulus upstream of the primary nozzle, on the mixing tube and diffuser walls, at the diffuser gap inlets and at the diffuser exit. The inlet flow swirl angle and flow temperature were varied to study their effect on ejector pumping, wall pressure, and wall temperature distribution. The data from bent ejectors were compared with similar data for a round straight ejector. The results showed that the 22.5° bent entraining ejector had better hot core cooling performance than the straight entraining ejector since the hot core was cooled by the tertiary flow more efficiently at the outer side of the bend.

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.

An Oscillating Backpressure Regulator for Low Flow Rate, High-Pressure Coreflooding Experiments

1982 ◽  
Vol 22 (06) ◽  
pp. 899-901
Author(s):  
W.O. Lease
Keyword(s):  
High Pressure ◽  
Electrical Signal ◽  
Back Pressure ◽  
Flow Coefficient ◽  
Error Signal ◽  
Pressure Regulator ◽  
Flow Rates ◽  
Core Flow ◽  
The Core ◽  
Valve Stem

Summary An oscillating back pressure regulator (OBPR) has been developed that is capable of accurately controlling backpressures as high as 6,000 psi at flow rates ranging from approximately 1 to 100 mL/hr. It has been applied successfully in C02/crude oil core flooding experiments involving the simultaneous flow of three fluid phases. The device is assembled easily from off-the-shelf components. Introduction To develop an understanding of complex EOR processes such as C02 flooding, experiments sometimes must be conducted in reservoir core samples at in-situ pressures, temperatures, and flow rates. For this purpose, a variable-restrictor-type back pressure regulator has been developed capable of handling flow rates on the order of I nil/hr (and as high as 100 ml/hr) while maintaining a constant back pressure as high as 6,000 psi with + 1 -psi accuracy. Theory and Practice It is clearly recognized that the flow coefficient of any valving system suitable for controlling flow must cover the flow rate range of interest, or little or no regulation can result. In core flow work, where flows are measured in milliliters per hour, the flow coefficients required for valves and regulators are quite low-typically of the order of 10 -6 L/hr/psi or evenless. Flow coefficients of this order are very difficult, if not impossible, to obtain in conventional, dome-loaded back pressure regulator.,. A further complication with that type regulator when used in core flow work is its large internal volume in relation to the PV of the core. In analyzing the flow coefficient curves of commercially available metering valves, one would not predict any such valve to be suitable for core flow work. The reason is that the very special requirements of core flow work are never considered in the design purpose of the valve. In setting up our high-pressure core flow equipment, the use of a variable restrictor was only one of several methods for back pressuring the system that we intended to investigate. However, a bench trial using a metering valve to control pressure manually at 2,000 psi with a constant flow of 5 mL/hr showed so much promise that other methods tentatively were discarded. The valve is usable as received. but performance can be improved considerably by polishing the valve stem and chamfering the valve seat to match more nearly the curvature of the valve stem shoulder. This technique improves the flow control at near the cutoff point and also, if properly performed, can make the valve nearly leak tight. To modulate this metering valve in a feedback system as a function of pressure, we coupled it to a small DC timing motor driven by operational amplifier signal conditioning circuitry. Fig. 1 is a simplified flow diagram of our flow systems. The transducers produce an electrical signal of + 10 V DC for a full-scale output on the strip chart recorder. The deviation of the electrical signal from pressure transducer T1 with respect to a setpoint signal produces the error signal for our controller. Instead of using a 2,000-psi transducer for generating this error signal, we chose a 100- to 200-psi transducer connected between a soft but constant reference pressure and the core outflow pressure. This arrangement pneumatically amplifies the error signal 10- to 20-fold, pneumatically amplifies the error signal 10- to 20-fold, without the generation of undue electrical noise otherwise produced by electrical amplification. SPEJ p. 899

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.

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.

scholarly journals Net-exergetic, hydraulic and thermal optimization of coaxial heat exchangers using fixed flow conditions instead of fixed flow rates

2021 ◽  
Vol 9 (1) ◽  
Author(s):  
Tobias Blanke ◽  
Markus Hagenkamp ◽  
Bernd Döring ◽  
Joachim Göttsche ◽  
Vitali Reger ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Laminar Flow ◽  
Mass Flow ◽  
Flow Rate ◽  
Heat Exchangers ◽  
Circular Ring ◽  
Flow Conditions ◽  
Flow Rates ◽  
Mass Flow Rates ◽  
Pipe Radius

AbstractPrevious studies optimized the dimensions of coaxial heat exchangers using constant mass flow rates as a boundary condition. They show a thermal optimal circular ring width of nearly zero. Hydraulically optimal is an inner to outer pipe radius ratio of 0.65 for turbulent and 0.68 for laminar flow types. In contrast, in this study, flow conditions in the circular ring are kept constant (a set of fixed Reynolds numbers) during optimization. This approach ensures fixed flow conditions and prevents inappropriately high or low mass flow rates. The optimization is carried out for three objectives: Maximum energy gain, minimum hydraulic effort and eventually optimum net-exergy balance. The optimization changes the inner pipe radius and mass flow rate but not the Reynolds number of the circular ring. The thermal calculations base on Hellström’s borehole resistance and the hydraulic optimization on individually calculated linear loss of head coefficients. Increasing the inner pipe radius results in decreased hydraulic losses in the inner pipe but increased losses in the circular ring. The net-exergy difference is a key performance indicator and combines thermal and hydraulic calculations. It is the difference between thermal exergy flux and hydraulic effort. The Reynolds number in the circular ring is instead of the mass flow rate constant during all optimizations. The result from a thermal perspective is an optimal width of the circular ring of nearly zero. The hydraulically optimal inner pipe radius is 54% of the outer pipe radius for laminar flow and 60% for turbulent flow scenarios. Net-exergetic optimization shows a predominant influence of hydraulic losses, especially for small temperature gains. The exact result depends on the earth’s thermal properties and the flow type. Conclusively, coaxial geothermal probes’ design should focus on the hydraulic optimum and take the thermal optimum as a secondary criterion due to the dominating hydraulics.

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