scholarly journals Swirl boundary layer and flow separation at the inlet of a rotating pipe

2016 ◽  
Vol 811 ◽  
pp. 350-371 ◽  
Author(s):  
F.-J. Cloos ◽  
D. Stapp ◽  
P. F. Pelz
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Flow Separation ◽  
Momentum Equation ◽  
Layer Growth ◽  
Boundary Layer Theory ◽  
Critical Flow ◽  
Flow Number ◽  
The Impact ◽  
Momentum Boundary Layer

When a fluid enters a rotating circular pipe, an angular momentum or swirl boundary layer appears at the wall and interacts with the axial momentum boundary layer. In the centre of the pipe, the fluid is free of swirl and is accelerated due to boundary layer growth. Below a critical flow number, defined as the ratio of average axial velocity to circumferential velocity of the pipe, there is flow separation, known in the turbomachinery context as part load recirculation. To describe this phenomenon analytically, we extended boundary layer theory to a swirl boundary layer interacting with the axial momentum boundary layer. The solution of the resulting generalized von Kármán momentum equation takes into account the influence of the Reynolds number and flow number. We show the impact of swirl on the axial boundary layer and conduct experiments in which we vary Reynolds number, flow number and surface roughness to validate the analytical results. The extended boundary layer theory predicts a critical flow number which is analytically derived and validated. Below this critical flow number, separation is expected.

Developing Swirl Boundary Layer and Flow Separation at the Inlet of a Coaxial Rotating Diffuser or Nozzle

2019 ◽  
Vol 141 (7) ◽  
Author(s):  
Ferdinand-J. Cloos ◽  
Peter F. Pelz
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Flow Separation ◽  
Axial Flow ◽  
Momentum Equation ◽  
Apex Angle ◽  
Critical Flow ◽  
Flow Number ◽  
Part Load ◽  
Reynolds Number Flow

When an axial flow enters a rotating diffuser or nozzle, a swirl boundary layer appears at the wall and interacts with the axial boundary layer. Below a critical flow number φc, there is a flow separation, known in the turbomachinery context as part load recirculation. This paper extends the previous work for a cylindrical coaxial rotating pipe still considering the influence of the centrifugal force by varying the pipe's radius, yielding a coaxial rotating circular diffuser or nozzle. The integral method of boundary layer theory is used to describe the flow at the inlet of a rotating circular diffuser or nozzle, obtaining a generalized von Kármán momentum equation. This work conducts experiments to validate the analytical results and shows the influence of Reynolds number, flow number, apex angle, and surface roughness on the boundary layers evolution. By doing so, a critical flow number for incipient flow separation is analytically derived, resulting in a stability map for part load recirculation depending on Reynolds number and apex angle. Hereby, positive apex angles (diffuser) and negative apex angles (nozzle) are considered.

Experimental Investigation of the Swirl Development at the Inlet of a Coaxial Rotating Diffuser or Nozzle

2019 ◽  
Vol 141 (4) ◽  
Author(s):  
Ferdinand-J. Cloos ◽  
Peter F. Pelz
Keyword(s):  
Boundary Layer ◽  
Flow Separation ◽  
Laser Doppler Anemometry ◽  
Layer Growth ◽  
Main Task ◽  
Flow Number ◽  
Axial Coordinate ◽  
Reynolds Number Flow ◽  
Number Flow ◽  
Boundary Layer Growth

When a fluid enters a rotating pipe, a swirl boundary layer with thickness of δ̃S appears at the wall and interacts with the axial momentum boundary layer with thickness of δ̃. The swirl is produced by the wall shear stress and not due to kinematic reasons as by a turbomachine. In the center of the pipe, the fluid is swirl-free and is accelerated due to axial boundary layer growth. Below a critical flow number φ < φc, there is flow separation, known in the turbomachinery context as part load recirculation. The previous work analyzes the flow at the inlet of a coaxial rotating circular pipe (R̃=R̃0). For a systematic approach to a turbomachine, the influence of the turbine's and pump's function, schematically fulfilled by a diffuser and a nozzle, on the evolution of the swirl and flow separation is to analyze. The radius of the rotating pipe depends linearly on the axial coordinate, yielding a rotating circular diffuser or nozzle. The swirl evolution depends on the Reynolds number, flow number, axial coordinate, and apex angle. The influence of the latter is the paper's main task. The circumferential velocity component is measured applying one-dimensional laser Doppler anemometry (LDA) to investigate the swirl evolution.

scholarly journals Numerical analysis of high-lift configurations with oscillating flaps

2021 ◽  
Author(s):  
Johannes Ruhland ◽  
Christian Breitsamter
Keyword(s):  
Reynolds Number ◽  
Flow Separation ◽  
Separated Flow ◽  
Navier Stokes ◽  
Rotational Axis ◽  
High Lift ◽  
Hinge Point ◽  
Reduced Frequency ◽  
Flap Deflection ◽  
The Impact

AbstractThis study presents two-dimensional aerodynamic investigations of various high-lift configuration settings concerning the deflection angles of droop nose, spoiler and flap in the context of enhancing the high-lift performance by dynamic flap movement. The investigations highlight the impact of a periodically oscillating trailing edge flap on lift, drag and flow separation of the high-lift configuration by numerical simulations. The computations are conducted with regard to the variation of the parameters reduced frequency and the position of the rotational axis. The numerical flow simulations are conducted on a block-structured grid using Reynolds Averaged Navier Stokes simulations employing the shear stress transport $$k-\omega $$ k - ω turbulence model. The feature Dynamic Mesh Motion implements the motion of the oscillating flap. Regarding low-speed wind tunnel testing for a Reynolds number of $$0.5 \times 10^{6}$$ 0.5 × 10 6 the flap movement around a dropped hinge point, which is located outside the flap, offers benefits with regard to additional lift and delayed flow separation at the flap compared to a flap movement around a hinge point, which is located at 15 % of the flap chord length. Flow separation can be suppressed beyond the maximum static flap deflection angle. By means of an oscillating flap around the dropped hinge point, it is possible to reattach a separated flow at the flap and to keep it attached further on. For a Reynolds number of $$20 \times 10^6$$ 20 × 10 6 , reflecting full scale flight conditions, additional lift is generated for both rotational axis positions.

Characterization of the Custom-Designed, High Reynolds Number Water Tunnel

2016 ◽  
Author(s):  
Yasaman Farsiani ◽  
Brian R. Elbing
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Test Section ◽  
High Reynolds Number ◽  
Layer Growth ◽  
Water Tunnel ◽  
Freestream Velocity ◽  
Section Design ◽  
High Reynolds

This paper reports on the characterization of the custom-designed high-Reynolds number recirculating water tunnel located at Oklahoma State University. The characterization includes the verification of the test section design, pump calibration and the velocity distribution within the test section. This includes an assessment of the boundary layer growth within the test section. The tunnel was designed to achieve a downstream distance based Reynolds number of 10 million, provide optical access for flow visualization and minimize inlet flow non-uniformity. The test section is 1 m long with 15.2 cm (6-inch) square cross section and acrylic walls to allow direct line of sight at the tunnel walls. The verification of the test section design was accomplished by comparing the flow quality at different location downstream of the flow inlet. The pump was calibrated with the freestream velocity with three pump frequencies and velocity profiles were measured at defined locations for three pump speeds. Boundary layer thicknesses were measured from velocity profile results and compared with analytical calculations. These measurements were also compared against the facility design calculations.

Some Measurements of Boundary-Layer Growth in a Two-Dimensional Diffuser

1959 ◽  
Vol 81 (3) ◽  
pp. 285-294 ◽  
Author(s):  
J. F. Norbury
Keyword(s):  
Boundary Layer ◽  
Static Pressure ◽  
Momentum Equation ◽  
Layer Growth ◽  
Area Ratio ◽  
Momentum Thickness ◽  
Two Dimensional ◽  
Static Pressure Distribution ◽  
Boundary Layer Growth ◽  
Flow Experiments

Low-speed experiments were carried out in a two-dimensional diffuser having a square throat and an area ratio of two to one. Measurements were made of static pressure distribution, velocity contours at throat and outlet, and boundary-layer growth along the four wall center lines. Visual flow experiments were performed using tufts and smoke filaments. Similar experiments were carried out with the throat boundary layers artificially thickened by means of round rods placed on the walls upstream. Disparities between the measured growth of momentum thickness and that predicted by the simple momentum equation are discussed, as well as the effect of the artificial thickening on diffuser efficiency.

scholarly journals Some hypersonic intake studies

2006 ◽  
Vol 110 (1105) ◽  
pp. 145-156 ◽  
Author(s):  
F. Lanson ◽  
J. L. Stollery
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Layer Growth ◽  
Isentropic Compression ◽  
Number Range ◽  
Principal Influence ◽  
Reynolds Number Range ◽  
Air Intake ◽  
Starting Process ◽  
Intake Flow

Abstract A ‘two dimensional’ air intake comprising a wedge followed by an isentropic compression has been tested in the Cranfield Gun Tunnel at Mach 8·2. These tests were performed to investigate qualitatively the intake flow starting process. The effects of cowl position, Reynolds number, boundary-layer trip and introduction of a small restriction in the intake duct were investigated. Schlieren pictures of the flow on the compression surface and around the intake entrance were taken. Results showed that the intake would operate over the Reynolds number range tested. Tests with a laminar boundary layer demonstrated the principal influence of the Reynolds number on the boundary-layer growth and consequently on the flow structure in the intake entrance. In contrast boundary layer tripping produced little variation in flow pattern over the Reynolds number range tested. The cowl lip position appeared to have a strong effect on the intake performance. The only parameter which prevented the intake from starting was the introduction of a restriction in the intake duct. The experimental data obtained were in good qualitative agreement with the CFD predictions. Finally, these experimental results indicated a good intake flow starting process over multiple changes of parameters.

Study of Flow Controlling on LP Turbine at Different Reynolds Number

2012 ◽  
Author(s):  
Muhammad Aqib Chishty ◽  
Hossein Raza Hamdani ◽  
Khalid Parvez ◽  
Muhammad Nafees Mumtaz Qadri
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Flow Separation ◽  
Separation Bubble ◽  
Low Pressure ◽  
Control Flow ◽  
Loss Coefficient ◽  
Shear Stresses ◽  
Low Pressure Turbine ◽  
Lp Turbine

Active and passive techniques have been used in the past, to control flow separation. Numerous studies were published on controlling and delaying the flow separation on low pressure turbine. In this study, a single dimple (i.e. passive device) is engraved on the suction side of LP turbine cascade T106A. The main aim of this research is to find out the optimum parameters of dimple i.e. diameter (D) and depth (h) which can produce strong enough vortex that can control the flow either in transition or fully turbulent phase. Furthermore, this optimal dimple is engraved to suppress the boundary layer separation at different Reynolds number (based on the chord length and inlet velocity). The dimple of different depth and diameter are used to find the optimal depth to diameter ratio. Computational results show that the optimal ratio of depth to diameter (h/D) for dimple is 0.0845 and depth to grid boundary layer (h/δ) is 0.5152. This optimized dimple efficiently reduces the normalized loss coefficient and it is found that the negative values of shear stresses found in uncontrolled case are being removed by the dimple. After that, dimple of optimized parameters are used to suppress the laminar separation bubble at different Re∼25000, 50000 and 91000. It was noticed that the dimple did not reduce the losses at Re∼25000. But at Re∼50000, it produced such a strong vortex that reduced the normalized loss coefficient to 25%, while 5% losses were reduced at Re∼91000. It can be concluded that the optimized dimple effectively controlled flow separation and reduced normalized loss coefficient from Re 25000 to 91000. As the losses are decreased, this will increase the low pressure turbine efficiency and reduce its fuel consumption.

An experimental investigation of turbulent spots and breakdown to turbulence

1960 ◽  
Vol 9 (2) ◽  
pp. 235-246 ◽  
Author(s):  
J. W. Elder
Keyword(s):  
Boundary Layer ◽  
Experimental Investigation ◽  
Reynolds Number ◽  
Hydrodynamic Stability ◽  
Free Stream ◽  
Stream Velocity ◽  
Turbulent Spot ◽  
Turbulent Spots ◽  
The Impact ◽  
Critical Intensity

The theory of hydrodynamic stability and the impact on it of recent work with turbulent spots is discussed. Emmons's (1951) assumptions about the growth and interaction of turbulent spots are found experimentally to be substantially correct. In particular it is shown that the region of turbulent flow on a flat plate is simply the sum of the areas that would be obtained if all spots grew independently.An investigation of the conditions required for breakdown to turbulence near a wall, that is, to initiate a turbulent spot, suggests that regardless of how disturbances are generated in a laminar boundary layer and independent of both the Reynolds number and the spatial extent of the disturbances, breakdown to turbulence occurs by the initiation of a turbulent spot at all points at which the velocity fluctuation exceeds a critical intensity. Over most of the layer this intensity is about 0·2 times the free-stream velocity. The Reynolds number is important merely in respect of the growth of disturbances prior to breakdown.

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