Single-mode plate flutter taking the boundary layer into account

2012 ◽  
Vol 47 (3) ◽  
pp. 417-429 ◽  
Author(s):  
V. V. Vedeneev
Keyword(s):  
Boundary Layer ◽  
Single Mode ◽  
Plate Flutter

Aeromechanic Response of a Coupled Inlet-Fan Boundary Layer Ingesting Distortion-Tolerant Fan

2019 ◽  
Author(s):  
G. S. Heinlein ◽  
M. A. Bakhle ◽  
J. P. Chen
Keyword(s):  
Boundary Layer ◽  
Wind Tunnel ◽  
Fluid Dynamic ◽  
Single Mode ◽  
Forced Response ◽  
Blade Vibration ◽  
Wind Tunnel Tests ◽  
Aerodynamic Damping ◽  
Insight Into ◽  
Tip Displacement

Abstract Boundary layer ingestion has significant potential to reduce fuel burn in aircraft engines. However, designing a fan that can operate in an environment of continuous distortion without aeromechanical failure is a critical challenge. Capturing the requisite aeromechanical flow features in a high-fidelity computational setting is necessary in validating satisfactory designs as well as determining possible regions for overall improvement. In the current work, a three-dimensional, time-accurate, Reynolds-averaged Navier-Stokes computational fluid dynamic code is utilized to study a distortion-tolerant fan coupled to a boundary layer ingesting inlet. The comparison between this coupled inlet-fan and a previous fan-only simulation will provide insight into the changes in aeromechanic response of the fan blades. Additionally, comparisons to previous wind tunnel tests are made to provide validation of inlet distortion as seen by the distortion-tolerant fan. A resonant crossing was also investigated for the 85% speed operational line condition to compare resonant response between the inlet-fan, fan-only, and experiment. A decrease in maximum tip displacement is observed in the forced response of the coupled inlet-fan compared to the fan-only simulation. The predicted maximum tip displacement was still below the upper limit on the range observed in the wind tunnel tests but matched well with the average tip displacement value of 27.6 mils. A single mode was chosen at the 100% speed condition to provide insight into the effects that the inlet duct has on fan stability. Near stall and near choke conditions were also simulated to observe how the changes of progressing along the speed line affects flutter stability prediction. The analysis shows the fan has low levels of aerodynamic damping at all the conditions tested. However, the coupled inlet-fan shows a decrease in the level of aerodynamic damping over what was observed with the fan-only simulation. Some of the blades experienced single cycles of negative aerodamping which indicate a possibility of increased blade vibration amplitude but were followed by positive aerodamping cycles. Work is continuing to understand possible sources to account for the differences observed between the two simulation cases as well as with the experiment.

Boundary-layer solutions of single-mode convection equations

1981 ◽  
Vol 102 ◽  
pp. 211-219 ◽  
Author(s):  
N. Riahi
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Rayleigh Number ◽  
Prandtl Number ◽  
Thermal Convection ◽  
Single Mode ◽  
Layer Method ◽  
Boundary Layer Method ◽  
Inertial Terms ◽  
Large Rayleigh Number

Nonlinear thermal convection between two stress-free horizontal boundaries is studied using the modal equations for cellular convection. Assuming a large Rayleigh number R the boundary-layer method is used for different ranges of the Prandtl number σ. The heat flux F is determined for the values of the horizontal wavenumber a which maximizes F. For a large Prandtl number, σ [Gt ] R⅙(log R)−1, inertial terms are insignificant, a is either of order one (for $\sigma \geqslant R^{\frac{2}{3}}$) or proportional to $R^{\frac{1}{3}}\sigma^{-\frac{1}{2}}$ (for $\sigma \ll R^{\frac{2}{3}}$) and F is proportional to $R^{\frac{1}{3}}$. For a moderate Prandtl number, \[ (R^{-1}\log R)^{\frac{1}{9}} \ll \sigma \ll R^{\frac{1}{6}}(\log R)^{-1}, \] inertial terms first become significant in an inertial layer adjacent to the viscous buoyancy-dominated interior, and a and F are proportional to R¼ and \[ R^{\frac{3}{10}}\sigma^{\frac{1}{5}} (\log\sigma R^{\frac{1}{4}})^{\frac{1}{10}}, \] respectively. For a small Prandtl number, $R^{-1} \ll \sigma \ll (R^{-1} \log R)^{\frac{1}{9}}$, inertial terms are significant both in the interior and the boundary layers, and a and F are proportional to ($R \sigma)^{\frac{9}{32}} (\log R\sigma)^{-\frac{1}{32}}$ and ($R \sigma)^{\frac{5}{16}} (\log R \sigma)^{\frac{3}{16}}$, respectively.

Micro-Optical Sensors for Boundary Layer Flow Studies

2006 ◽  
Author(s):  
Darius Modarress ◽  
Pavle Svitek ◽  
Katy Modarress ◽  
Daniel Wilson
Keyword(s):  
Boundary Layer ◽  
Flow Velocity ◽  
Optical Sensors ◽  
Boundary Layer Flow ◽  
Single Mode ◽  
Field Analysis ◽  
Optical Mems ◽  
Optical Elements ◽  
Wall Boundary Layer ◽  
Layer Flow

This manuscript describes optical MEMS (or MOEMS)-based microsensors for near wall boundary layer flow and particle field analysis. The sensors have been developed to measure a variety of parameters including flow velocity, surface speed, skin friction, and particle sizing. The surface mounted sensors measure flow velocity and/or flow velocity gradients as close as 70 microns from the wall. The sensors have been successfully used in a number of filed tests and flow facilities at different Reynolds numbers. They have also been used on-board full-scale vehicles. These compact and embeddable sensors incorporate specially designed diffractive optical elements and use single-mode optical fiber or integrated diode lasers for illumination.

Influence of the viscous boundary layer perturbations on single-mode panel flutter at finite Reynolds numbers

2018 ◽  
Vol 852 ◽  
pp. 578-601 ◽  
Author(s):  
Vsevolod Bondarev ◽  
Vasily Vedeneev
Keyword(s):  
Boundary Layer ◽  
Growth Rate ◽  
Single Mode ◽  
Reynolds Numbers ◽  
Instability Criterion ◽  
Panel Flutter ◽  
Arbitrary Form ◽  
Viscous Boundary Layer ◽  
Layer Effect ◽  
Viscous Boundary

Panel flutter is an aeroelastic instability of aircraft skin panels, which can lead to a reduction in service life and panel destruction. Despite the existence of many studies related to panel flutter, the influence of the boundary layer on the panel stability has been considered in only a few of them. Up to the present day, most papers on the boundary layer effect consider only a zero-pressure-gradient boundary layer over a flat plate. The only studies of a boundary layer of arbitrary form were conducted in our previous papers (Vedeneev, J. Fluid Mech., vol. 736, 2013, pp. 216–249 and Bondarev & Vedeneev, J. Fluid Mech., vol. 802, 2016, pp. 528–552), where the boundary layer was represented as an inviscid shear layer (the Reynolds number $R=\infty$). In this paper we investigate the problem, taking viscosity into account, at large but finite Reynolds numbers. As before, we assume that the panel length is large and use Kulikovskii’s global instability criterion to analyse the panel eigenmodes and consider two different types of boundary layer profiles: a generalised convex profile and a profile with a generalised inflection point. Results show that viscous perturbations can, in general, have both stabilising and destabilising effects on the system, depending on the velocity and temperature profiles of the boundary layer and on its thickness. However, surprisingly, we prove that if the boundary layer yields a significant growth rate in the inviscid approximation, then the viscosity always produces an even larger growth rate.

Resonance of the thermal boundary layer adjacent to an isothermally heated vertical surface

2013 ◽  
Vol 724 ◽  
pp. 305-336 ◽  
Author(s):  
Yongling Zhao ◽  
Chengwang Lei ◽  
John C. Patterson
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Frequency Band ◽  
High Frequency ◽  
Thermal Boundary Layer ◽  
Single Mode ◽  
Vertical Surface ◽  
Frequency Region ◽  
Transitional Region ◽  
High Frequency Band

AbstractThe instability characteristics and resonance of a natural convection boundary layer adjacent to an isothermally heated vertical surface are investigated using direct stability analyses. The detailed streamwise evolution of the boundary-layer frequencies is visualized via the power spectra of the temperature time series in the thermal boundary layer. It is found that the entire thermal boundary layer may be divided into three distinct regions according to the frequency profile, which include an upstream low-frequency region, a transitional region (with both low- and high-frequency bands) and a downstream high-frequency region. The high-frequency band in the downstream region determines the resonance characteristics of the thermal boundary layer, which can be triggered by a single-mode perturbation at frequencies within the high-frequency band. The single-mode perturbation experiments further reveal that the maximum resonance of the thermal boundary layer is triggered by a perturbation at the characteristic frequency of the boundary layer. For the boundary-layer flow at $\mathit{Ra}= 3. 6\times 1{0}^{10} $ and $\mathit{Pr}= 7$, a net heat transfer enhancement of up to 44 % is achieved by triggering resonance of the boundary layer. This significant enhancement of heat transfer is due to the resonance-induced advancement of the laminar–turbulent transition, which is found to be dependent on the perturbation frequency and amplitude. Evidence from different perspectives revealing the same position of the transition are provided and discussed. The outcomes of this investigation demonstrate the prospect of a resonance-based approach for enhancing heat transfer.

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