scholarly journals Sensitivity of a fluidic oscillator to modifications of feedback channel and mixing chamber geometry

2021 ◽  
Vol 62 (12) ◽  
Author(s):  
Abdul Raouf Tajik ◽  
Kursat Kara ◽  
Vladimir Parezanović
Keyword(s):  
Flow Regime ◽  
Static Pressure ◽  
Flow Behavior ◽  
Pressure Fluctuations ◽  
External Flow ◽  
Surface Shape ◽  
Feedback Channel ◽  
Time Resolved ◽  
Auto Correlation ◽  
Mixing Chamber

Abstract This experimental study investigates the effects of internal geometry modifications on the performance of a curved Sweeping Jet actuator. The modifications are applied to the geometry of the feedback channel and the mixing chamber Coanda surface, and the resulting actuator properties are evaluated using time-resolved static pressure measurements inside the actuator and hot-wire measurements of the external flow. The major result is that small, localized modifications of the curved sweeping jet actuator geometry can lead to a complete change in the external flow regime, making the jet velocity distribution homogeneous, similar to the angled variant of the actuator. The Coanda surface shape is identified as the primary cause of the external jet adopting the bifurcated or homogeneous flow regime. The relationships between the sweeping frequency, jet deflection angle, required supply pressure, and pressure fluctuations are analyzed and discussed in detail. External flow behavior and coherence are characterized by phase-averaged, phase-locked velocity profiles and auto-correlation of the velocity signals. Graphical abstract

Air to Air Ejector with Various Divergent Mixing Chambers

2014 ◽  
Vol 493 ◽  
pp. 50-55
Author(s):  
Václav Dvořák
Keyword(s):  
Experimental Investigation ◽  
Static Pressure ◽  
Pressure Fluctuations ◽  
Mixing Process ◽  
Mixing Processes ◽  
Process Characteristics ◽  
Pressure Distributions ◽  
Mixing Chamber ◽  
Air Ejector ◽  
Mixing Chambers

The article deals with experimental investigation of subsonic air to air ejector with various configurations of the mixing chamber and the diffuser. A constant mixing chamber, 2° and 4° divergent mixing chambers and 6° diffuser were applied to find differences in the mixing process. Characteristics of the ejector, static pressure distributions and pressure fluctuations were measured to find how the different shape of the mixing chamber affect the efficiency of mixing processes. Pressure fluctuation increased rapidly while the ejection ratio was higher than 1.25 and the highest efficiency of the ejector was obtained when using configuration 4-4-6.

Effect of Clocking on the Second Stator Pressure Field of a One and a Half Stage Transonic Turbine

2004 ◽  
Author(s):  
J. Gadea ◽  
R. De´nos ◽  
G. Paniagua ◽  
N. Billiard ◽  
C. H. Sieverding
Keyword(s):  
Pressure Distribution ◽  
Static Pressure ◽  
Pressure Field ◽  
Pressure Fluctuations ◽  
Leading Edge ◽  
Fast Response ◽  
Time Resolved ◽  
Pressure Transducers ◽  
Static Pressure Distribution ◽  
Transonic Turbine

This paper focuses on the experimental investigation of the time-averaged and time-resolved pressure field of a second stator tested in a one and a half stage high-pressure transonic turbine. The effect of clocking and its influence on the aerodynamic and mechanical behaviour are investigated. The test program includes four different clocking positions, i.e. relative pitch-wise positions between the first and the second stator. Pneumatic probes located upstream and downstream of the second stator provide the time-averaged component of the pressure field. For the second stator airfoil, both time-averaged and time-resolved surface static pressure fields are measured at 15, 50 and 85% span with fast response pressure transducers. Regarding the time-averaged results, the effect of clocking is mostly observed in the leading edge region of the second stator, the largest effects being observed at 15% span. The surface static pressure distribution is changed locally, which is likely to affect the overall performance of the airfoil. The phase-locked averaging technique allows to process the time-resolved component of the data. The pressure fluctuations are attributed to the passage of pressure gradients linked to the traversing of the upstream rotor. The pattern of these fluctuations changes noticeably as a function of clocking. Finally, the time-resolved pressure distribution is integrated along the second stator surface to determine the unsteady forces applied on the vane. The magnitude of the unsteady force is very dependent on the clocking position.

A Comparison of Measured and Predicted Unsteadiness in a Transonic Fan

1998 ◽  
Author(s):  
Udai K. Singh ◽  
Graham C. Smith
Keyword(s):  
Continuous Flow ◽  
Static Pressure ◽  
Pressure Fluctuations ◽  
Test Rig ◽  
Time Resolved ◽  
Flow Test ◽  
Blade Row ◽  
Transonic Fan ◽  
Blade Row Interaction ◽  
Highly Loaded

The two dimensional, viscous, non-linear unsteady code UNSFLO has been used to model a highly loaded transonic fan stage along a mid-span section. This paper examines the results of this unsteady calculation, and compares with time resolved measurements taken on a continuous flow test rig. The main features of the time resolved experimental data are shown to be captured by the calculation. Comparison of losses for steady and unsteady calculations show that the stator loss is significantly increased by the blade row interaction effects. The origin of static pressure fluctuations within the stator passage has also been examined.

Effect of Clocking on the Heat Transfer Distribution of a Second Stator Tested in a One and a Half Stage HP Turbine

2005 ◽  
Author(s):  
N. Billiard ◽  
G. Paniagua ◽  
R. De´nos
Keyword(s):  
Heat Transfer ◽  
Static Pressure ◽  
Pressure Fluctuations ◽  
High Heat ◽  
Point Of View ◽  
Gas Temperature ◽  
Isentropic Compression ◽  
Time Resolved ◽  
High Heat Transfer ◽  
Inlet Conditions

This paper reports detailed heat transfer measurements on the second stator of a one and a half stage HP turbine. The tests are performed under engine representative conditions. Four vane-to-vane clocking positions are investigated. The second stator inlet and outlet flowfield is monitored. The heat transfer measurements are performed with thin-film gauges around the blade profile at 15%, 50% and 85% span as well as on the hub and casing endwalls. On a time-averaged point of view, the inlet conditions of the second stator vary noticeably as a function of clocking. This variation is due to a change of relative position of the total pressure pitchwise distribution, linked to the first stator, with respect to the pitchwise variation of the static pressure, linked to the second stator. On the hub platform, the location of a zone of high heat transfer, probably due to high velocity levels, moves in conjunction with the clocking. When this zone is in the center of the passage, the time-averaged thermal load around the airfoil profile is significantly lower. On a time-resolved point of view, the rotor exit Mach number undergoes periodically short excursions in the transonic regime. The passing of these shock/potential distortion events can be clearly seen on the second stator profile. Thanks to a model of isentropic compression, it is demonstrated that the heat flux variations originate in static pressure fluctuations that are causing variations in the gas temperature. The clocking changes not only the mean levels of the heat transfer but also the intensity and the trajectory of the fluctuations.

The Time-Resolved Internal and External Flow Field Properties of a Fluidic Oscillator

2014 ◽  
Author(s):  
Sarah Gaertlein ◽  
Rene Woszidlo ◽  
Florian Ostermann ◽  
C. Nayeri ◽  
Christian O. Paschereit
Keyword(s):  
Flow Field ◽  
External Flow ◽  
Time Resolved ◽  
Fluidic Oscillator

Exploring Applicability of Acoustic Heat Transfer Enhancement Across Various Perturbation Elements

2021 ◽  
Vol 143 (3) ◽  
Author(s):  
Tapish Agarwal ◽  
Maximilian Stratmann ◽  
Simon Julius ◽  
Beni Cukurel
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Static Pressure ◽  
Pressure Fluctuations ◽  
Acoustic Excitation ◽  
Internal Cooling ◽  
Transfer Enhancement ◽  
Number Range ◽  
Flow Modulation ◽  
Spatially Resolved

Abstract The requirements of improved heat transfer performance on turbine surfaces and internal cooling passages drive the research into exploring new methods for efficiency enhancements. The addition of ribbed structures inside the cooling ducts has proven to be most practical, which increases heat transfer from surfaces to fluid flow at the cost of some pressure loss. Many active and passive methods have been proposed for enhancing the heat transfer, where acoustic excitation has been recently shown to be an effective option. Moreover, the existing pressure fluctuations due to rotor–stator interactions can also be utilized as a source of excitation. However, the sensitivity of the phenomenon to various flow and geometric parameters has not been fully characterized. The present study investigates various aspects of convective heat transfer enhancement and turbulent flow modulation caused by acoustic forcing on separating and reattaching flow over isolated rib obstacles. A parametric study is conducted; rib obstacles of various sizes and shapes (including rectangular, squared, triangular, and semi-cylindrical) are installed in a low-speed, fully turbulent wind tunnel, and measurements are taken at different velocities and excitation frequencies. Static pressure and spatially resolved surface temperature measurements are performed to quantify the ramifications of acoustic excitation on the wetted wall. Within the favorable Strouhal number range of 0.1–0.25, an optimum value of 0.16 is observed. It is shown that triangular ribs are more prone to acoustic heat transfer enhancement than rectangular or cylindrical perturbations. A linear correlation between static pressure recovery rate and acoustic heat transfer enhancement is observed, which is invariant to change in size/shape of the rib as well as flow and excitation parameters.

scholarly journals On Damping and Fluidelastic Instability in a Tube Bundle Subjected to Two-Phase Cross-Flow

2007 ◽  
Author(s):  
Joaquin E. Moran ◽  
David S. Weaver
Keyword(s):  
Flow Regime ◽  
Void Fraction ◽  
Tube Bundle ◽  
Damping Ratio ◽  
Pressure Fluctuations ◽  
Cross Flow ◽  
Phase Changes ◽  
Working Fluid ◽  
Two Phase ◽  
Fluidelastic Instability

An experimental study was conducted to investigate damping and fluidelastic instability in tube arrays subjected to two-phase cross-flow. The purpose of this research was to improve our understanding of these phenomena and how they are affected by void fraction and flow regime. The working fluid used was Freon 11, which better models steam-water than air-water mixtures in terms of vapour-liquid mass ratio as well as permitting phase changes due to pressure fluctuations. The damping measurements were obtained by “plucking” the monitored tube from outside the test section using electromagnets. An exponential function was fitted to the tube decay trace, producing consistent damping measurements and minimizing the effect of frequency shifting due to fluid added mass fluctuations. The void fraction was measured using a gamma densitometer, introducing an improvement over the Homogeneous Equilibrium Model (HEM) in terms of density and velocity predictions. It was found that the Capillary number, when combined with the two-phase damping ratio (interfacial damping), shows a well defined behaviour depending on the flow regime. This observation can be used to develop a better methodology to normalize damping results. The fluidelastic results agree with previously presented data when analyzed using the HEM and the half-power bandwidth method. The interfacial velocity is suggested for fluidelastic studies due to its capability for collapsing the fluidelastic data. The interfacial damping was introduced as a tool to include the effects of flow regime into the stability maps.

Design of a Transonic High-Pressure Turbine Stage 2D Section With Reduced Rotor/Stator Interaction

2004 ◽  
Author(s):  
Michele Vascellari ◽  
Re´my De´nos ◽  
Rene´ Van den Braembussche
Keyword(s):  
Rotor Blade ◽  
Static Pressure ◽  
Aerodynamic Force ◽  
Pressure Fluctuations ◽  
Uniform Field ◽  
Turbine Stage ◽  
Rotor Stator Interaction ◽  
Transonic Turbine ◽  
Blade Failure ◽  
Rotor Profiles

In transonic turbine stages, the exit static pressure field of the vane is highly non-uniform in the pitchwise direction. The rotor traverses periodically this non-uniform field and large static pressure fluctuations are observed around the rotor section. As a consequence the rotor blade is submitted to significant variations of its aerodynamic force. This contributes to the high cycle fatigue and may result in unexpected blade failure. In this paper an existing transonic turbine stage section is redesigned in the view of reducing the rotor stator interaction, and in particular the unsteady rotor blade forcing. The first step is the redesign of the stator blade profile to reduce the stator exit pitchwise static pressure gradient. For this purpose, a procedure using a genetic algorithm and an artificial neural network is used. Next, two new rotor profiles are designed and analysed with a quasi 3D Euler unsteady solver in order to investigate their receptivity to the shock interaction. One of the new profiles allows reducing the blade force variation by 50%.

Exploring Applicability of Acoustic Heat Transfer Enhancement Across Various Perturbation Elements

2020 ◽  
Author(s):  
Tapish Agarwal ◽  
Maximilian Stratmann ◽  
Simon Julius ◽  
Beni Cukurel
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Static Pressure ◽  
Pressure Fluctuations ◽  
Acoustic Excitation ◽  
Internal Cooling ◽  
Transfer Enhancement ◽  
Number Range ◽  
Flow Modulation ◽  
Spatially Resolved

Abstract The requirements of improved heat transfer performance on turbine surfaces and internal cooling passages drive the research into exploring new methods for efficiency enhancements. Addition of ribbed structures inside the cooling ducts has proven to be most practical, which increases heat transfer from surfaces to fluid flow at the cost of some pressure loss. Many active and passive methods have been proposed for enhancing the heat transfer, where acoustic excitation has been recently shown to be an effective option. Moreover, the existing pressure fluctuations due to rotor-stator interactions can also be utilized as a source of excitation. However, the sensitivity of the phenomenon to various flow and geometric parameters has not been fully characterized. The present study investigates various aspects of convective heat transfer enhancement and turbulent flow modulation caused by acoustic forcing on separating and reattaching flow over isolated rib obstacles. A parametric study is conducted; rib obstacles of various sizes and shapes (including rectangular, squared, triangular, semi-cylindrical, etc.) are installed in a low-speed, fully turbulent wind tunnel and measurements are taken at different velocities and excitation frequencies. Static pressure and spatially resolved surface temperature measurements are performed to quantify the ramifications of acoustic excitation on the wetted wall. Within the favorable Strouhal number range of 0.1–0.25, an optimum value of 0.16 is observed. It is shown that triangular ribs are more prone to acoustic heat transfer enhancement than rectangular or cylindrical perturbations. A linear correlation between static pressure recovery rate and acoustic heat transfer enhancement is observed, which is invariant to change in size/shape of the rib as well as flow and excitation parameters.

Calculation of Aerodynamic Noise for Centrifugal Fan of Air-Conditioner

2013 ◽  
Author(s):  
Taku Iwase ◽  
Hideshi Obara ◽  
Hiroyasu Yoneyama ◽  
Yoshinobu Yamade ◽  
Chisachi Kato
Keyword(s):  
Sound Pressure ◽  
Static Pressure ◽  
Pressure Fluctuations ◽  
Coarse Grid ◽  
Aerodynamic Noise ◽  
Absolute Velocity ◽  
Centrifugal Fan ◽  
Air Conditioner ◽  
Simulation Code ◽  
Fine Grid

Flow fields in a centrifugal fan for an indoor unit of an air-conditioner were calculated with finite element method-based large eddy simulation (LES) with the aim of predicting fan performance and aerodynamic noise in this study. The numerical simulation code employed throughout the LES was called FrontFlow/blue (FFB). We compared 10M grid [coarse grid] and 60M grid [fine grid] calculation results for investigation of influence of grid resolution. In the fine grid, the number of grid elements in blade-to-blade direction, and of region between the shroud and the bell mouth increased in particular. By calculating with the fine grid, calculated distributions of absolute velocities at blade exit reasonably agreed with experimental results. Because of this, maximum absolute velocity by fine grid near hub decreased as compared to those by coarse grid. Calculated sound pressure level by fine grid was therefore smaller than that by coarse grid, and the overestimation of sound pressure was suppressed by calculating with fine grid. This decrease of the absolute velocity was a first factor for the improvement of calculation accuracy. Moreover, number of captured streaks on the blade, hub, and shroud surfaces by fine grid increased as compared to those by coarse grid. As a result, size of streak by fine grid became smaller than that by coarse grid. Static pressure fluctuations by fine grid on the blade, hub, and shroud surfaces therefore reduced as compared to those by coarse grid. Aerodynamic noise was related to static pressure fluctuations according to Curle’s equation. This reduction of static pressure fluctuations was therefore a second factor for improvement of calculation accuracy.

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