Experimental Investigations of a High Frequency Master-Slave Fluidic Oscillator to Achieve Independent Frequency and Mass Flow Characteristics

2016 ◽  
Author(s):  
Valentin Bettrich ◽  
Reinhard Niehuis
Keyword(s):  
Boundary Layer ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
High Frequency ◽  
Turbine Blades ◽  
Coupled Oscillator ◽  
Fluidic Oscillator ◽  
Low Pressure Turbine ◽  
Highly Loaded

High frequency fluidic oscillators have been of scientific interest for many decades. Especially over the last couple of years fluidic oscillators became more important for active flow control applications. At the Institute of Jet Propulsion of the University of the German Federal Armed Forces Munich studies on different kinds of flow control methods were carried out on aerodynamically highly loaded low pressure turbine blades. On the basis of these studies, the most efficient way to trigger transition at low Reynolds numbers was found to be with fluidic oscillators at frequencies up to 10 kHz. Still, it is an open issue whether it is most efficient to trigger Tollmien-Schlichting waves, stimulate Kelvin-Helmholtz instabilities or simply induce a frequency independent disturbance in form of a periodic impulse for boundary layer control on aero-dynamically highly loaded low pressure turbine blades. To find an answer to these questions, a high frequency master-slave fluidic oscillator is introduced with an independent frequency and mass flow characteristic. Any frequency from the master oscillator’s characteristic can be chosen and the mass flow rate can be controlled with the slave oscillator. Contrary to concepts with fast switching valves or piezo actuators, this actuator is based on a working principle without the necessity of any moving and life limited parts. Based on experimental results, the characteristics of the master as well as the coupled oscillator are shown. The predictable operation of the coupled device is demonstrated in detail for a constant overall mass flow rate at discrete frequencies of 5 and 6 kHz. In addition, it is also shown that the mass flow can be varied with one master-slave arrangement by a factor of six while keeping the frequency constant at 5 or 6 kHz, respectively. Besides proof of concept these investigations focus on relevant parameters for active boundary layer and transition control. The frequency and velocity spectra of the coupled device are presented for constant frequency and constant mass flow operating points. Based on these results the improvement potential of the coupled oscillator for fundamental research on this topic is discussed.

Application of Air Microblowing Through a Porous Wall for Skin Friction Reduction on a Flat Plate

2010 ◽  
Vol 5 (3) ◽  
pp. 38-46
Author(s):  
Vladimir I. Kornilov ◽  
Andrey V. Boiko
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
Skin Friction ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Porous Wall ◽  
Friction Reduction ◽  
Local Skin ◽  
Skin Friction Reduction

The effect of air microblowing through a porous wall on the properties of a turbulent boundary layer formed on a flat plate in an incompressible flow is studied experimentally. The Reynolds number based on the momentum thickness of the boundary layer in front of the porous insert is 3 900. The mass flow rate of the blowing air per unit area was varied within Q = 0−0.0488 кg/s/m2 . A consistent decrease in local skin friction, reaching up to 45−47 %, is observed to occur at the maximal blowing air mass flow rate studied.

Air Blowing Into Boundary Layer Of A Flat Plate With Length-Dependent Permeability

2016 ◽  
Vol 11 (3) ◽  
pp. 16-26
Author(s):  
Vladimir Kornilov ◽  
Andrey Boiko ◽  
Ivan Kavun ◽  
Anatoliy Popkov
Keyword(s):  
Boundary Layer ◽  
Friction Coefficient ◽  
Flat Plate ◽  
Skin Friction ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Skin Friction Coefficient ◽  
Air Blowing ◽  
The Mean

A generalized analysis of the results of numerical and experimental studies of air blowing into a turbulent boundary layer through finely perforated surface consisting of alternating permeable and impermeable sections of varying length providing a sudden change in the flow conditions at the boundaries of these sections is presented. The air blowing coefficient Cb determined by the mass flow rate per unit area of the active perforated sample varied in the range from 0 to 0.008. It is shown that as Cb grows, the maximum reduction in the mean surface skin-friction coefficient CF, which is the value through the permeable area of perforated sample, reaches about 65 %. When keeping the equal mass flow rate Q for all tested combinations, the mean skin-friction coefficient remains constant, independent of geometrical parameters of permeable and impermeable sections. Increasing the length of the last permeable section leads to the growth of relaxation region which is characterized by the reduced skin friction values on the impermeable part of the flat plate.

Flow Field in the Tip Gap of a Planar Cascade of Turbine Blades

1989 ◽  
Vol 111 (3) ◽  
pp. 276-283 ◽  
Author(s):  
M. Yaras ◽  
Yingkang Zhu ◽  
S. A. Sjolander
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Pressure Difference ◽  
Good Accuracy ◽  
Flow Direction ◽  
Turbine Blades ◽  
Rate Distribution ◽  
Velocity Magnitude ◽  
The Relationship

Measurements are presented for the flow in the tip gap of a planar cascade of turbine blades. Three clearances of from 2.0 to 3.2 percent of the blade chord were considered. Detailed surveys of the velocity magnitude, flow direction, and total pressure within the gap were supplemented by blade surface and endwall static pressure measurements. The results help to clarify the relationship between the leakage mass flow rate distribution and the driving pressure differences. It was found that even for the present relatively large clearances, fluid near the endwall experiences a pressure difference that is comparable with the blade pressure difference. It is also shown that a simple model can predict with good accuracy the mass flow rate distribution and the magnitude and direction of the velocity vectors within the gap.

Focusing and Defocusing Effects in a Single Liquid-Core/Liquid-Clad Optical Waveguide: An Optical Coupler

2011 ◽  
Author(s):  
Seyed Reza Mahmoudi
Keyword(s):  
Boundary Layer ◽  
Mass Flow Rate ◽  
Optical Waveguide ◽  
Mass Flow ◽  
Flow Rate ◽  
Wall Temperature ◽  
Thermal Boundary Layer ◽  
Flow Direction ◽  
Liquid Core ◽  
Optical Coupler

A single-liquid-core/liquid-clad L2 optical waveguide/coupler is studied numerically. The device consists of a large aspect ratio-microchannel isothermally heated on its both parallel flat walls. Steady state laminar Poiseuille flow of cold water which is introduced to the heated-microchannel forms a stable thermal boundary layer adjacent to the isothermal heated walls. Thermal boundary layer development causes the lateral refractive index gradient across the channel which is required for waveguiding. At a particular mass flow rate for a given wall temperature, the waveguiding occurs. Since the thermal boundary layer, cladding region, is actively tunable through varying both surface temperature and mass flow rate, The waveguiding effect along the channel is highly configurable. We demonstrated that the excitation in the flow direction leads to defocusing of the beam at fundamental TE mode. By reversing the flow direction, the Counter-flow excitation of the waveguide also results in focusing effects. The current waveguide can be exploited as an integrated optical coupler at specific channel wall temperature and mass flow rate.

scholarly journals Theoretical and Experimental Investigation of a 34 Watt Radial-Inflow Steam Turbine With Partial-Admission

2020 ◽  
Author(s):  
Patrick H. Wagner ◽  
Jan Van herle ◽  
Jürg Schiffmann
Keyword(s):  
Steam Turbine ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Pressure Ratio ◽  
Turbine Blades ◽  
Tip Clearance ◽  
Experimental Results ◽  
Partial Admission ◽  
Blade Tip

Abstract A micro steam turbine with a tip diameter of 15 mm was designed and experimentally characterized. At the nominal mass flow rate and total-to-total pressure ratio of 2.3 kg h−1 and 2, respectively, the turbine yields a power of 34 W and a total-to-static isentropic efficiency of 37%. The steam turbine is conceived as a radial-inflow, low-reaction (15%), and partial admission (21%) machine. Since the steam mass flow rate is limited by the heat provided of the system (solid oxide fuel cell), a low-reaction and high-power-density design is preferred. The partial-admission design allows for reduced losses: The turbine rotor and stator blades are prismatic, have a radial chord length of 1 mm and a height of 0.59 mm. Since the relative rotor blade tip clearance (0.24) is high, the blade tip leakage losses are significant. Considering a fixed steam supply, this design allows to increase the blade height, and thus reducing the losses. The steam turbine drives a fan, which operates at low Mach numbers. The rotor is supported on dynamic steam-lubricated bearings; the nominal rotational speed is 175 krpm. A numerical simulation of the steam turbine is in good agreement with the experimental results. Furthermore, a novel test rig setup, featuring extremely-thin thermocouples (ϕ0.15 mm) is investigated for an operation with ambient and hot air at 220 °C. Conventional zero and one-dimensional pre-design models correlate well to the experimental results, despite the small size of the turbine blades.

Impact of Air Microblowing Through a Permeable Wall on a Turbulent Boundary Layer

2011 ◽  
Vol 6 (1) ◽  
pp. 77-83
Author(s):  
Vladimir I. Kornilov ◽  
Andrey V. Boiko ◽  
Anatoliy N. Popkov
Keyword(s):  
Boundary Layer ◽  
Skin Friction ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Friction Reduction ◽  
Permeable Wall ◽  
Sample Length ◽  
Local Skin ◽  
Boundary Layer Equations

The effectiveness of air microblowing through a permeable wall to reduce a turbulent skin friction over a flat plate in an incompressible flow is studied experimentally and theoretically. The mass flow rate of the blowing air per unit area was varied within Q = 0−0.05 kg 2 m s . A consistent decrease in local skin friction is observed to occur both at the increasing blowing air mass flow rate and along the permeable sample length. No appreciable influence of nondimensional microhole diameter on skin-friction reduction along the length of permeable sample is observed. The experimental results are compared with data of calculation that carried out within the boundary-layer equations

scholarly journals Combustion Characteristics of Multi-Element Swirl Coaxial Jet Injectors under Varying Momentum Ratios

Energies ◽  
2021 ◽  
Vol 14 (13) ◽  
pp. 4064
Author(s):  
Younseok So ◽  
Yeoungmin Han ◽  
Sejin Kwon
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Turbine Blades ◽  
Liquid System ◽  
Combustion Characteristics ◽  
Combustion Stability ◽  
Inlet Temperature ◽  
Combustion Gas ◽  
Combustion Pressure

The combustion characteristics of a staged combustion cycle engine with an oxidizer-rich preburner were experimentally studied at different momentum ratios of multi-element injectors. Propellants were simultaneously supplied as a liquid–liquid–liquid system, and an injector was designed in which a swirl coaxial jet is sprayed. The injector burned the propellants in the inner chamber which had a temperature greater than 2000 K. To cool the combustion gas, a liquid oxidizer was supplied to the cooling channel outside the injector. To prevent the turbine blades from melting, the temperature of the combustion gas was maintained below 700 K. To confirm the combustion characteristics at different momentum ratios of the high-temperature combustion gas inside the injector and the low-temperature liquid oxidizer outside the injector, three types of injectors were designed and manufactured with different momentum ratios: MR 3.0, MR 3.3, and MR 3.7. In this study, the results of the combustion test for each type were compared for 30 s. For ORPB-A, a combustion pressure of 18.5 MPaA, fuel mass flow rate of 0.26 kg/s, oxidizer mass flow rate of 15.3 kg/s, and turbine inlet temperature of 686 K were obtained in the combustion stability period of 29.0–29.5 s. The combustion efficiency was 98% for MR 3.0 (ORPB-A), which was superior to that for other momentum ratios. In addition, during the combustion test for MR 3.0, the fluctuations in the characteristic velocity, combustion pressure, and propellant mass flow rate were low, indicating that combustion was stable. The three types of combustion instability were all less than 0.8%, thus confirming that the combustion stability was excellent.

scholarly journals Development of Disturbances in the Supersonic Boundary Layer under Helium Injection from the Surface

2022 ◽  
Vol 16 (2) ◽  
pp. 41-47
Author(s):  
V. I. Lysenko ◽  
B. V. Smorodsky ◽  
A. D. Kosinov
Keyword(s):  
Boundary Layer ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Supersonic Boundary Layer ◽  
Natural Disturbances

Experiments on the influence of distributed injection of helium on the development of the supersonic boundary layer unstable disturbances have been performed. It is revealed, that injection of helium in a certain range of blowing mass flow rate, leads to a certain decrease of spatial amplification rates of natural disturbances.

Sign in / Sign up

Export Citation Format

Share Document