Measurements of the Entrainment Coefficient of Acoustically Pulsed Axisymmetric Free Air Jets

1992 ◽  
Vol 114 (2) ◽  
pp. 409-415 ◽  
Author(s):  
P. J. Vermeulen ◽  
P. Rainville ◽  
V. Ramesh
Keyword(s):  
Strouhal Number ◽  
Excitation Power ◽  
Axial Distance ◽  
Nozzle Orifice ◽  
Air Jets ◽  
Air Jet ◽  
Free Air ◽  
Direct Measurements ◽  
Entrainment Coefficient ◽  
Initial Zone

Novel direct measurements of the entrainment coefficient in the initial zone of a pulsating air jet have been successfully accomplished. A series of pulsating air jets flowing from different nozzle orifice sizes into surrounding air were investigated for the effects of jet axial length, excitation power, and Strouhal number. The entrainment coefficient of the excited jet varied strongly with axial distance downstream of the orifice exit plane and with pulsation strength. The acoustic drive considerably increased the entrainment coefficient by up to 4.6 times at 10 diameters downstream of the nozzle. There was only a tendency for the entrainment coefficient to increase with the Strouhal number and hence an optimum Strouhal number for jet response was not found.

scholarly journals Measurements of the Entrainment Coefficient of Acoustically Pulsed Axisymmetric Free Air Jets

1991 ◽  
Author(s):  
P. J. Vermeulen ◽  
P. Rainville ◽  
V. Ramesh
Keyword(s):  
Strouhal Number ◽  
Excitation Power ◽  
Axial Distance ◽  
Nozzle Orifice ◽  
Air Jets ◽  
Air Jet ◽  
Free Air ◽  
Direct Measurements ◽  
Entrainment Coefficient ◽  
Initial Zone

Novel direct measurements of the entrainment coefficient in the initial zone of a pulsating air jet have been successfully accomplished. A series of pulsating air jets flowing from different nozzle orifice sizes into surrounding air were investigated for the effects of jet axial length, excitation power and Strouhal number. The entrainment coefficient of the excited jet varied strongly with axial distance downstream of the orifice exit plane and with pulsation strength. The acoustic drive considerably increased the entrainment coefficient by up to 4.6 times at 10 diameters downstream of the nozzle. There was only a tendency for the entrainment coefficient to increase with the Strouhal number and hence an optimum Strouhal number for jet response was not found.

Measurements of Entrainment by Acoustically Pulsed Axisymmetric Air Jets

1986 ◽  
Vol 108 (3) ◽  
pp. 479-484 ◽  
Author(s):  
P. J. Vermeulen ◽  
V. Ramesh ◽  
Wai Keung Yu
Keyword(s):  
Strouhal Number ◽  
Exit Plane ◽  
Downstream Distance ◽  
Air Jets ◽  
Upper Limit ◽  
Direct Measurements

Direct measurements of entrainment by acoustically pulsed axisymmetric air jets flowing into surrounding air have been made for a range of orifice sizes, Strouhal numbers, and excitation powers. The entrainment was considerably increased, by up to 5.8 times at distances greater than 15 diameters axially downstream of the orifice exit plane. The entrainment of the excited jet varied linearly with downstream distance. The jet response varied nonlinearly with excitation strength, indicating that there may be a practical upper limit to the acoustic augmentation of entrainment. The response depends on Strouhal number and appears to be optimum at about 0.25.

Twin Pulsating Jets Impingement Heat Transfer for Fuel Preheating in Automotives

2014 ◽  
Vol 663 ◽  
pp. 322-328 ◽  
Author(s):  
Ali Ahmed Gitan ◽  
Rozli Zulkifli ◽  
Kamaruzaman Sopian ◽  
Shahrir Abdullah
Keyword(s):  
Heat Transfer ◽  
Ignition Process ◽  
Pulsation Frequency ◽  
Ir Camera ◽  
Copper Target ◽  
Air Jets ◽  
Air Jet ◽  
Impingement Heat Transfer ◽  
Pulsating Jet ◽  
Pulsating Jets

The problem of environmental pollution and depletion of fossil fuel can be reduced in automotives by using an alternative bio-fuel and improve the ignition process in engine. Both solutions need to use the fuel preheating technique. This work presents the idea of fuel preheating by using exhaust impingement on the fuel tank. Heat transfer between twin pulsating hot air jets and flat copper target was investigated as an application for preheating of automotive fuel to improve ignition process in the engine. The nozzle of 20 mm was used to produce air jet of Reynolds number, Re ≃ 5500 and a temperature of 54°C. The impinged target was imposed to still air surrounding at temperature of 24°C. Pulsating frequencies of 10-50 Hz were applied on air jets by using twin pulsating jet mechanism. The effect of pulsation frequency on heat transfer was measured using IR camera and heat flux-temperature micro foil sensor. The results obtained by both of these methods showed well agreement. Also, the results revealed significant influence of flow rate difference between steady and pulsating jet cases. In addition, the highest Nusselt number, Nu ≃ 7.2, was obtained at pulsation frequency of 20 Hz.

Mixing of an Acoustically Excited Air Jet With a Confined Hot Crossflow

1992 ◽  
Vol 114 (1) ◽  
pp. 46-54 ◽  
Author(s):  
P. J. Vermeulen ◽  
P. Grabinski ◽  
V. Ramesh
Keyword(s):  
Strouhal Number ◽  
Temperature Profiles ◽  
Measured Temperature ◽  
Mixing Zone ◽  
Wake Region ◽  
Mixing Processes ◽  
Jet Mixing ◽  
Air Jet ◽  
Percent Increase ◽  
Jet Structure

The mixing of an acoustically pulsed air jet with a confined hot crossflow has been assessed by temperature profile measurements. These novel experiments were designed to examine the effects of acoustic driver power and Strouhal number on jet structure, penetration, and mixing. The results showed that excitation produced strong changes in the measured temperature profiles. This resulted in significant increases in mixing zone size, penetration (at least 100 percent increase), and mixing, and the length to achieve a given mixed state was shortened by at least 70 percent. There was strong modification to the jet-wake region. The increase in jet penetration and mixing was saturating near 90 W, the largest driving power tested. The jet response as determined by penetration and mixing was optimum at a Strouhal number of 0.27. Overall, pulsating the jet flow significantly improved the jet mixing processes in a controllable manner.

Fluid mechanical aspects of open- and closed-toe flue organ pipe voicing

2011 ◽  
Vol 2 (2) ◽  
pp. 284-295
Author(s):  
D. Steenbrugge
Keyword(s):  
Pressure Measurements ◽  
Jet Instability ◽  
Active Involvement ◽  
Air Jets ◽  
Air Jet ◽  
Hole Area ◽  
Power Regulation ◽  
Organ Pipes ◽  
Organ Pipe ◽  
Jet Characteristics

Open- and closed-toe voicing of flue organ pipes constitute two opposite extremes of possible ways todetermine the air-jet flow rate through the flue. The latter method offers more voicing control parametersand thus more flexibility, at the expense of a necessary pressure loss at the toe hole. Another differencebetween both cases arises from different air-jet characteristics, such as velocity profile, Re number, flowmomentum or aspect ratio, the latter influencing jet instability. Furthermore, for closed-toe voicing, the flowfield in the pipe foot is modified by an axisymmetric air jet created through the highly constricted toe hole.Velocity measurements on air jets, pressure measurements in the pipe foot are presented, compared anddiscussed for both voicing methods. The ratio of flue to toe hole area is shown to be the sole pipeparameter to entirely determine the jet velocity and can be useful to quantitatively characterize flue and toehole voicing. Open-toe voicing turns out to be the more delicate and low-pressure only method becauseany modification of the flue has consequences on all aspects of the pipe operation, whereas the closed-toemethod, in connection with higher pressures and with active involvement of cut-up adjustment, allows someseparation between sound timbre and power regulation.

scholarly journals Experimental testing of exterior wall mounted mechanical ventilation exhaust air outlet devices

2021 ◽  
Vol 246 ◽  
pp. 02001
Author(s):  
Ülar Palmiste ◽  
Tauno Meier ◽  
Jarek Kurnitski ◽  
Hendrik Voll
Keyword(s):  
Mechanical Ventilation ◽  
Experimental Testing ◽  
Airflow Rate ◽  
Tracer Gas ◽  
Qualitative Comparison ◽  
Smoke Visualization ◽  
Air Jets ◽  
Air Jet ◽  
Building Wall ◽  
Face Velocity

The purpose of the study was to experimentally test the performance of four types of wall-mounted mechanical ventilation exhaust air outlet devices. A full-scale mock-up of a segment of an external wall with an exhaust air outlet was constructed. The tested exhaust air devices include a gravity louver, fixed-blade louver, louver plate, and exhaust nozzle. The performance assessment included two types of experiments over the exhaust airflow rate range of 25–94 l/s at isothermal conditions with no influencing wind: (i) the particle tracer method with smoke to visualize the exhaust air jets from the outlets, and (ii) the tracer gas method to measure the dilution of CO2 concentration in the exhaust air jet. Furthermore, the aerodynamic performance was comparatively evaluated in terms of pressure drop and exhaust air face velocity at the outlet. The qualitative comparison of airflow patterns by smoke visualization showed notable differences between the tested device types. Concentration decrease evaluation indicated that the exhaust air pollutants are more efficiently transported away from the building wall by exhaust outlets that discharge at 0–45 degrees downwards from the horizontal plane. Discharge angles 60–90 degrees downwards produced a wall-attached jet and the pollutant tracer concentration remained relatively high in the vicinity of the wall.

scholarly journals An Experimental Study of the Mixing by an Acoustically Pulsed Axisymmetrical Air-Jet

1985 ◽  
Author(s):  
P. J. Vermeulen ◽  
Wai Keung Yu
Keyword(s):  
Experimental Study ◽  
Temperature Profile ◽  
Strouhal Number ◽  
Jet Flow ◽  
Velocity Pulsation ◽  
Entrainment Rate ◽  
Air Jet ◽  
Toroidal Vortices

The mixing by an acoustically pulsed axisymmetrical air-jet, flowing into the atmosphere, has been studied by means of velocity and temperature profile measurements. The strength of the velocity pulsation imparted to the jet flow and of the associated toroidal vortices were also measured. The entrainment rate was increased by up to two times, with the majority of the extra entrainment occurring over the first five diameters downstream of the jet orifice, where toroidal vortices are formed and attain their greatest strength. The jet response depends on Strouhal number and appears to be optimum at about 0.25. The response starts to saturate at the limit of pulsation strength used.

NOx Measurements for Combustor With Acoustically Controlled Primary Zone

1997 ◽  
Vol 119 (3) ◽  
pp. 559-565 ◽  
Author(s):  
P. J. Vermeulen ◽  
V. Ramesh
Keyword(s):  
Operating Conditions ◽  
Gas Temperature ◽  
Mixing Processes ◽  
Jet Mixing ◽  
Air Jets ◽  
Air Jet ◽  
A Value ◽  
Primary Zone ◽  
Turbine Design ◽  
Lean Conditions

Successful NOx measurements at the end of the primary zone of a small tubular combustor of conventional gas turbine design, employing acoustically controlled primary zone air-jet mixing processes, have been made at scaled 1/4 and 1/8 load operating conditions. Testing at 1/8 load significantly increased the effective strength of the acoustic drive, which strongly improved the mixing by the acoustically driven primary zone air-jets. The acoustic drive caused partial blockage of the combustor primary zone airflow. This increased the equivalence ratio and the gas temperature, and made the gas temperature distribution more uniform, except for lean conditions at 1/8 load, in the plane of the NOx measurements. This explained the measured greater NOx “with-drive,” and the distinctly more uniform NOx distribution, which confirmed that mixing was acoustically augmented. The acoustically produced changes were greater at 1/8 load. The acoustic drive significantly changed the combustor operating characteristic so far as mean NOx was concerned, and under lean conditions at 1/8 load mean NOx was reduced, indicating that a value of 10 ppm is possible (a 50 percent reduction).

scholarly journals Use of Air Infiltration in Swine Housing Ventilation System Design

2019 ◽  
Vol 35 (3) ◽  
pp. 325-338
Author(s):  
H T Jadhav ◽  
S J Hoff
Keyword(s):  
Ventilation System ◽  
Three Dimensional ◽  
Design Procedure ◽  
Field Testing ◽  
Air Distribution ◽  
Air Jets ◽  
Air Infiltration ◽  
Air Jet ◽  
Archimedes Number ◽  
Ventilation Systems

Abstract.The objective of this research was to develop and analyze the procedure for using recent air infiltration (AI) data collected from commercial swine finishing rooms (SFRs) in the design of negative pressure mechanical ventilation systems (VSs). Air infiltration is an integral part of any ventilation process. Infiltration reduces the pressure differential across planned inlets and at very low pressure differences, cold air jets may drop directly on the animals causing significant discomfort. In this article, a design procedure is proposed for swine housing ventilation systems with the influence of air infiltration included. The method was used on one SFR for which air infiltration data was collected by in-field testing. The air-jet throw, jet momentum number, a newly developed coverage factor, and Archimedes number were used to assess the influence of infiltration on predicted air-jet and fresh-air distribution and to help guide the design of planned inlets in SFR VSs with known infiltration. The analysis completed quantifies the severity of AI on air-jet and air distribution performance, and suggests that for the analysis room to ventilate properly requires a 50% reduction in AI levels beyond field measured curtain and fan infiltration. The analysis completed suggests a method for systematically planning three-dimensional ceiling inlet placement and operation and provides design guidance for new ceiling inlets suitable for SFR VSs. Keywords: Air distribution, Air-jets, Archimedes number, Infiltration, Jet Momentum Number.

Measurements of Entrainment on a Rotating Disc

1967 ◽  
Vol 71 (680) ◽  
pp. 587-587
Author(s):  
T. S. Cham ◽  
M. R. Head
Keyword(s):  
Boundary Layer ◽  
Velocity Distribution ◽  
Total Pressure ◽  
Rotating Disc ◽  
Free Air ◽  
Direct Measurements

In an earlier note Case reported direct measurements of entrainment on a rotating disc. More comprehensive measurements, made subsequently to those of Case and using essentially the same technique, are reported here. Two different sizes of drum were used in the present investigation, the flow within the drum in each case being smoothed by the use of a honeycomb and screens as well as a baffle at entry (see Fig. 1).The entrainment was also deduced from yawmeter and total pressure traverses through the boundary layer on the disc in free air, the integrated crossflow component of the velocity distribution through the layer evidently representing the entrainment up to the radius at which the traverses were performed. A typical measured crossflow profile is shown in Fig. 2.

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