scholarly journals Boundary layer state detection using piezoelectric sensors

2021 ◽  
Author(s):  
Vincent L. Stuber ◽  
Marios Kotsonis ◽  
Sybrand van der Zwaag
Keyword(s):  
Boundary Layer ◽  
Separated Flow ◽  
Fast Response ◽  
Electrical Signal ◽  
Time Resolved ◽  
Mechanical Coupling ◽  
Single Data Point ◽  
Layer Flow ◽  
Single Data ◽  
Naca 0012

Abstract Two piezoelectric series bimorph sensors were embedded below the skin of a NACA 0012 symmetrical airfoil to detect the local state of the boundary layer during wind tunnel testing. Small vanes piercing the airfoil skin were glued onto the bimorphs providing a mechanical coupling to the local mechanical force fluctuations imparted by the local unsteady boundary layer flow. The state of the boundary layer at the sensor sites was varied by changing the angle of attack. The objective of this work was to establish the ability of this sensor concept to accurately distinguish among typical boundary layer states such as attached laminar flow, turbulent flow and separated flow. The output of the sensor was compared to concurrent time-resolved particle image velocimetry measurements, which served as a validation technique. Using the developed sensor response envelope, a single data point time series of the piezo electrical signal was proven to be sufficient to accurately detect the boundary layer state on classical airfoils in the low Reynolds number regime. In projected future applications, single or arrays of bimorph sensors can be used to map the boundary layer of more complex or morphing shape airfoils. The fast response of the sensor can in principle be utilised in closed-loop flow control systems, aimed at drag reduction or lift enhancement.

On the Periodically Unsteady Interaction of Wakes, Secondary Flow Development and Boundary Layer Flow in an Annular LPT Cascade: Part 1 — Experimental Investigation

2018 ◽  
Author(s):  
Martin Sinkwitz ◽  
Benjamin Winhart ◽  
David Engelmann ◽  
Francesca di Mare ◽  
Ronald Mailach
Keyword(s):  
Boundary Layer ◽  
Secondary Flow ◽  
Boundary Layer Flow ◽  
Measurement Data ◽  
Separated Flow ◽  
Experimental Investigations ◽  
Suction Surface ◽  
Time Resolved ◽  
Unsteady Interaction ◽  
Layer Flow

The results reported in this two-part — combined experimental and numerical — paper address the time-dependent impact of periodically unsteady wakes on the development of profile and end wall boundary layers and consequently on the secondary flow system. Experimental investigations are conducted on an annular 1.5 stage axial turbine rig at Ruhr-Universität Bochum’s Chair of Thermal Turbomachines and Aeroengines. The object under investigation is a modified T106 profile LPT stator row at a representative exit flow Reynolds number of 200,000. By making use of an annular geometry instead of a linear cascade, the influence of curvilinear end walls, non-uniform, increasing pitch across span and radial flow migration can be represented. Incoming wakes are generated by a variable-speed driven rotor equipped with cylindrical bars. Special emphasis is put on the wake-induced recurrent formation, suppression, weakening and displacement of individual vortices and separated flow regimes. For this, based on a comprehensive set of time-resolved measurement data, the interaction of impinging bar wakes and boundary layer flow and thus separation and its periodic manipulation along the passage end walls and on the blade suction surface are studied within the frequency domain.

A Method for the Calculation of 3D Boundary Layers on Practical Wing Configurations

1981 ◽  
Vol 103 (1) ◽  
pp. 104-111 ◽  
Author(s):  
J. P. F. Lindhout ◽  
G. Moek ◽  
E. De Boer ◽  
B. Van Den Berg
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Boundary Layer Flow ◽  
Eddy Viscosity ◽  
Separated Flow ◽  
Laminar Boundary Layers ◽  
Eddy Viscosity Model ◽  
Airplane Wing ◽  
Turbulent Boundary Layer Flow ◽  
Layer Flow

This paper gives a description of a calculation method for 3D turbulent and laminar boundary layers on nondevelopable surfaces. A simple eddy viscosity model is incorporated in the method. Special attention is given to the organization of the computations to circumvent as much as possible stepsize limitations. The method is also able to proceed the computation around separated flow regions. The method has been applied to the laminar boundary layer flow over a flat plate with attached cylinder, and to a turbulent boundary layer flow over an airplane wing.

Boundary Layer Separation Control With Fluidic Oscillators

2009 ◽  
Vol 131 (4) ◽  
Author(s):  
Ciro Cerretelli ◽  
Kevin Kirtley
Keyword(s):  
Boundary Layer ◽  
Large Scale ◽  
Separated Flow ◽  
Boundary Layer Separation ◽  
Maximum Pressure ◽  
Suction Surface ◽  
Stator Vane ◽  
Average Operating ◽  
Fluidic Actuators ◽  
Layer Flow

Fluidic oscillating valves have been used in order to apply unsteady boundary layer injection to “repair” the separated flow of a model diffuser, where the hump pressure gradient represents that of the suction surface of a highly loaded stator vane. The fluidic actuators employed in this study consist of a fluidic oscillator that has no moving parts or temperature limitations and is therefore more attractive for implementation on production turbomachinery. The fluidic oscillators developed in this study generate an unsteady velocity with amplitudes up to 60% rms of the average operating at nondimensional blowing frequencies (F+) in the range of 0.6<F+<6. These actuators are able to fully reattach the flow and achieve maximum pressure recovery with a 60% reduction of injection momentum required and a 30% reduction in blowing power compared with optimal steady blowing. Particle image velocimetry velocity and vorticity measurements have been performed, which show no large-scale unsteadiness in the controlled boundary layer flow.

scholarly journals On 3D Flow Structure of the Boundary Layer on the Suction Side of a Plate

2018 ◽  
Vol 180 ◽  
pp. 02112 ◽  
Author(s):  
Václav Uruba ◽  
Pavel Procházka ◽  
Vladislav Skála
Keyword(s):  
Boundary Layer ◽  
Experimental Study ◽  
Flat Plate ◽  
Boundary Layer Flow ◽  
Suction Side ◽  
Flow Dynamics ◽  
3D Flow ◽  
Time Resolved ◽  
Piv Technique ◽  
Layer Flow

Experimental study of the structure of the boundary layer on the suction side of a plate is to be presented. The flat plate with rounded edges and angle of attack of 7° is used. The boundary layer flow will be explored using the time-resolved PIV technique, measuring plane was located very close to the wall. Analysis of the flow dynamics is to be presented using the POD technique applied on both velocity and vorticity fields.

Boundary Layer Separation Control With Fluidic Oscillators

2006 ◽  
Author(s):  
Ciro Cerretelli ◽  
Kevin Kirtley
Keyword(s):  
Boundary Layer ◽  
Large Scale ◽  
Separated Flow ◽  
Boundary Layer Separation ◽  
Maximum Pressure ◽  
Suction Surface ◽  
Stator Vane ◽  
Average Operating ◽  
Fluidic Actuators ◽  
Layer Flow

Fluidic oscillating valves have been used in order to apply unsteady boundary layer injection to repair the separated flow of a model diffuser, where the hump pressure gradient represents that of the suction surface of a highly loaded stator vane. The fluidic actuators employed in this study consist of a fluidic oscillator that has no moving parts or temperature limitations and therefore is more attractive for implementation on production turbomachinery. The fluidic oscillators developed in this study generate an unsteady velocity with amplitudes up to 60% RMS of the average operating at non-dimensional blowing frequencies (F+) in the range 0.6 < F+ < 6. These actuators are able to fully reattach the flow and achieve maximum pressure recovery with a 60% reduction of injection momentum required and a 30% reduction in blowing power compared to optimal steady blowing. PIV velocity and vorticity measurements have been performed that show no large-scale unsteadiness in the controlled boundary layer flow.

Flow Studies of the Leading Edge Stall on a Swept-Back Wing at High Incidence

1956 ◽  
Vol 60 (541) ◽  
pp. 51-60 ◽  
Author(s):  
Joseph Black
Keyword(s):  
Boundary Layer ◽  
Liquid Film ◽  
Boundary Layer Flow ◽  
Separation Bubble ◽  
Flow Direction ◽  
Separated Flow ◽  
Leading Edge ◽  
Outer Edge ◽  
Layer Flow ◽  
Wing Tip

SummaryThe flow separation on a swept-back wing with 44 degrees leading edge sweep at 18 degrees incidence has been investigated by means of detailed pressure distribution measurements over the leading edge, boundary layer flow determination with liquid film technique, and yawmeter traverses. A wool-tuft grid was also used, and a spin detector was developed to search for regions of vorticity. These tests established that the flow separates on the leading edge; over the inboard sections it re-attaches behind a “ short” separation bubble, while outboard it only re-attaches near the trailing edge, thus forming a “ long ” separation bubble, or else fails to attach. The separated flow in what has been commonly called the tip stall does in fact take the form of a “ ram's horn “ vortex with the origin, or “ tip,” located at the junction of the two bubbles on the leading edge. The vortex lies outwards across the wing surface at approximately 20 to 25 degrees to the line-of-flight before curving aft to be shed into the wake, where it extends almost from mid semi-span to the wing tip. This vortex induces considerable changes in flow direction, both on and over the wing, and also in the wake. Thus in the wake a maximum downwash of 23 degrees is induced aft of the mid semi-span, and there is an upwash of 17 degrees at the outer edge of the vortex, almost aft of the tip. A good correlation between yawmeter results and the boundary layer flow direction indications from the liquid film technique was obtained.

On the Periodically Unsteady Interaction of Wakes, Secondary Flow Development, and Boundary Layer Flow in An Annular Low-Pressure Turbine Cascade: An Experimental Investigation

2019 ◽  
Vol 141 (9) ◽  
Author(s):  
Martin Sinkwitz ◽  
Benjamin Winhart ◽  
David Engelmann ◽  
Francesca di Mare ◽  
Ronald Mailach
Keyword(s):  
Boundary Layer ◽  
Secondary Flow ◽  
Boundary Layer Flow ◽  
Measurement Data ◽  
Separated Flow ◽  
Low Pressure ◽  
Experimental Investigations ◽  
Suction Surface ◽  
Low Pressure Turbine ◽  
Layer Flow

The experimental results reported in this contribution address the time-dependent impact of periodically unsteady wakes on the development of profile and end wall boundary layers and consequently on the secondary flow system. Experimental investigations are conducted on an annular 1.5 stage axial turbine rig at Ruhr-Universität Bochum’s Chair of Thermal Turbomachines and Aeroengines. The object under investigation is a modified T106 profile low-pressure turbine (LPT) stator row at a representative exit flow Reynolds number of 200,000. By making use of an annular geometry instead of a linear cascade, the influence of curvilinear end walls, nonuniform, increasing pitch across the span and radial flow migration can be represented. Incoming wakes are generated by a variable-speed driven rotor equipped with cylindrical bars. Special emphasis is put on the wake-induced recurrent formation, suppression, weakening, and displacement of individual vortices and separated flow regimes. For this, based on a comprehensive set of time-resolved measurement data, the interaction of impinging bar wakes and boundary layer flow and thus separation and its periodic manipulation along the passage end walls and on the blade suction surface are studied within the frequency domain.

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