Investigation on a Type of Flow Control to Weaken Unsteady Separated Flows by Unsteady Excitation in Axial Flow Compressors

2004 ◽  
Author(s):  
Xin-Qian Zheng ◽  
Xiao-Bo Zhou ◽  
Sheng Zhou
Keyword(s):  
Wide Spectrum ◽  
Excitation Frequency ◽  
Axial Flow ◽  
Maximum Velocity ◽  
Excitation Amplitude ◽  
High Order Scheme ◽  
Wide Range ◽  
Optimal Excitation ◽  
Suction And Blowing ◽  
Axial Flow Compressors

By solving unsteady Reynolds-averaged 2-D N-S equations discretized by a high-order scheme, the results showed that the disordered unsteady separated flow could be effectively controlled by periodic suction and blowing in a wide range of incidence, resulting in enhancement of time-averaged aerodynamic performances. The effects of unsteady excitation frequency, amplitude and excitation location were investigated in detail. The effective excitation frequency spans a wide spectrum and there is an optimal excitation frequency that is nearly equal to the Characteristic frequency of vortex shedding. Excitation amplitude exhibits a threshold value (nearly 10% in term of the ratio of maximum velocity of periodic suction and blowing to the velocity of free flow) and an optimal value (nearly 35%). The optimal excitation location is just upstream of the separation point. We also explored feasible unsteady actuators by utilizing upstream wake for constraining unsteady separation in axial flow compressors.

Investigation on a Type of Flow Control to Weaken Unsteady Separated Flows by Unsteady Excitation in Axial Flow Compressors

2004 ◽  
Vol 127 (3) ◽  
pp. 489-496 ◽  
Author(s):  
Xin-qian Zheng ◽  
Xiao-bo Zhou ◽  
Sheng Zhou
Keyword(s):  
Stokes Equations ◽  
Wide Spectrum ◽  
Excitation Frequency ◽  
Axial Flow ◽  
Maximum Velocity ◽  
Compressor Cascade ◽  
Wide Range ◽  
Optimal Excitation ◽  
Suction And Blowing ◽  
Axial Flow Compressors

By solving unsteady Reynolds-averaged Navier-Stokes equations discretized by a high-order scheme, the results showed that the disordered unsteady separated flow could be effectively controlled by periodic suction and blowing in a wide range of incidences, resulting in enhancement of time-averaged aerodynamic performances of an axial compressor cascade. The effects of unsteady excitation frequency, amplitude, and excitation location were investigated in detail. The effective excitation frequency spans a wide spectrum, and there is an optimal excitation frequency that is nearly equal to the characteristic frequency of vortex shedding. Excitation amplitude exhibits a threshold value (nearly 10% in terms of the ratio of maximum velocity of periodic suction and blowing to the velocity of free flow) and an optimal value (nearly 35%). The optimal excitation location is just upstream of the separation point. We also explored feasible unsteady actuators by utilizing the upstream wake for constraining unsteady separation in axial flow compressors.

Compressibility Effects on the Two Generations of Unsteady Flow Types in Axial Flow Compressors

2005 ◽  
Author(s):  
Xinqian Zhen ◽  
Sheng Zhou ◽  
Anping Hou ◽  
Jinsong Xiong
Keyword(s):  
Unsteady Flow ◽  
Axial Flow ◽  
Separated Flows ◽  
Design System ◽  
Relative Reduction ◽  
Positive Effects ◽  
Flow Type ◽  
Wide Range ◽  
Two Generations ◽  
Axial Flow Compressors

There occurred unsteady separated flows inside axial flow compressors, which was however not taken into consideration in the present aerodynamic design system. This discrepancy indicates that the potential underlying unsteady separated flows is yet to be explored, hence the present research team proposes the concept of two generations of unsteady flow types, i.e. Unsteady Natural Flow Type (UNFT) and Unsteady Cooperative Flow Type (UCFT). Numerical simulations are carried out in the present paper to study the compressibility effect on the unsteady cooperative flow type in axial flow compressors. The studies show that aerodynamic performances are remarkably enhanced by means of transforming the flow type from UNFT into UCFT by imposing unsteady excitations. In the case of 2D subsonic cascade, performances are greatly improved in a wide range of Ma number (Ma < 0.8) and the maximum relative reduction of the loss coefficient reaches 40.2%. In the case of 2D trans-supersonic cascade, positive effects can’t be captured. However, in the case of a 3D trans-supersonic single rotor, the adiabatic efficiency is increased from 87.0% to 90.2%.

Energy Absorption and Dissipation Performance in Cycloid Guided Pendulum Absorbers

2010 ◽  
Author(s):  
Younes Rashidi ◽  
Siamak Arzanpour ◽  
Mehrzad Tabatabaian
Keyword(s):  
Energy Dissipation ◽  
Energy Absorption ◽  
Excitation Frequency ◽  
Excitation Amplitude ◽  
Maximum Energy ◽  
Single Frequency ◽  
Vibration Absorbers ◽  
Wide Range ◽  
Induced Motion ◽  
Energy Absorbers

The dynamic energy absorbers are auxiliary systems that are attached to the main structure and widely used as a simple solution for neutralization of vibrations. Among various types of pendulum vibration absorbers are preferable for high-rise buildings, bridges and other civil structures for suppression earthquake-excited vibrations. The problem in dissipating vibration of earthquake is its unknown characteristics such as excitation frequency and magnitude. As a result, designing of an effective self tuning vibration absorber that can adjust its performance according to the excitation frequency will be a challenge. The situation is to have an absorber that can respond at a single frequency for wide range of excitation amplitude so its parameter can be well adjusted for the maximum energy dissipation. It is shown [5] that period in cycloid pendulum is constant for large amplitude. This feature is a major advantage of cycloid pendulum absorbers that could be used in combination with an energy dissipation mechanism to reduce the induced motion in a structure. In this paper, two types of vibration absorbers, i.e., simple and cycloid pendulum are analytically compared. The simulation results demonstrate the superiority of the cycloid damper type in energy absorption/dissipation over a simple pendulum one.

Cucurbitacins as Anticancer Agents: A Patent Review

2019 ◽  
Vol 14 (2) ◽  
pp. 133-143 ◽  
Author(s):  
Hidayat Hussain ◽  
Ivan R. Green ◽  
Muhammad Saleem ◽  
Khanzadi F. Khattak ◽  
Muhammad Irshad ◽  
...  
Keyword(s):  
Anticancer Agents ◽  
Wide Spectrum ◽  
Biological Effects ◽  
Therapeutic Effects ◽  
Cytotoxic Effects ◽  
Natural Sources ◽  
Oh Groups ◽  
Drug Candidates ◽  
The Past ◽  
Wide Range

Background: Cucurbitacins belong to a group of tetracyclic triterpenoids that display a wide range of biological effects. In the past, numerous cucurbitacins have been isolated from natural sources and many active compounds have been synthesized using the privileged scaffold in order to enhance its cytotoxic effects. Objective: his review covers patents on the therapeutic effects of natural cucurbitacins and their synthetic analogs published during the past decade. By far, the majority of patents published are related to cancer and Structure-Activity Relationships (SAR) of these compounds are included to lend gravitas to this important class of natural products. Methods: The date about the published patents was downloaded via online open access patent databases. Results: Cucurbitacins display significant cytotoxic properties, in particular cucurbitacins B and D which possess very potent effects towards a number of cancer cells. Numerous cucurbitacins isolated from natural sources have been derivatized through chemical modification at the C(2)-OH and C(25)- OH groups. Most importantly, an acyl ester of the C(25)-OH and, iso-propyl, n-propyl and ethyl ether groups of the C(2)-OH demonstrated the most increased cytotoxic activity. Conclusion: The significant cytotoxic effects of natural and semi-synthetic cucurbitacins make them attractive as new drug candidates. Moreover, cucurbitacins have the capability to form conjugates with other anticancer drugs which will synergistically enhance their anticancer effects. The authors believe that in order to get lead compounds, there should be a greater focus on the synthesis of homodimers, heterodimers, and halo derivatives of cucurbitacins. In the opinion of the authors the analysis of the published patents on the cucurbitacins indicates that these compounds can be developed into a regimen to treat a wide spectrum of cancers.

scholarly journals Greater trochanteric pain syndrome: Evaluation and management of a wide spectrum of pathology

2021 ◽  
Vol 9 ◽  
pp. 205031212110225
Author(s):  
Mark A Pianka ◽  
Joseph Serino ◽  
Steven F DeFroda ◽  
Blake M Bodendorfer
Keyword(s):  
Wide Spectrum ◽  
Pain Syndrome ◽  
Operative Management ◽  
Hip Pain ◽  
Greater Trochanteric Pain Syndrome ◽  
Trochanteric Bursitis ◽  
Treatment Indications ◽  
Careful Clinical Examination ◽  
Wide Range ◽  
Tendon Pathology

Greater trochanteric pain syndrome is a common cause of lateral hip pain, encompassing a spectrum of disorders, including trochanteric bursitis, abductor tendon pathology, and external coxa saltans. Greater trochanteric pain syndrome is primarily a clinical diagnosis, and careful clinical examination is essential for accurate diagnosis and treatment. A thorough history and physical exam may be used to help differentiate greater trochanteric pain syndrome from other common causes of hip pain, including osteoarthritis, femoroacetabular impingement, and lumbar stenosis. Although not required for diagnosis, plain radiographs and magnetic resonance imaging may be useful to exclude alternative pathologies or guide treatment of greater trochanteric pain syndrome. The majority of patients with greater trochanteric pain syndrome respond well to conservative management, including physical therapy, non-steroidal anti-inflammatory drugs, and corticosteroid injections. Operative management is typically indicated in patients with chronic symptoms refractory to conservative therapy. A wide range of surgical options, both open and endoscopic, are available and should be guided by the specific etiology of pain. The purpose of this review is to highlight pertinent clinical and radiographic features used in the diagnosis and management of greater trochanteric pain syndrome. In addition, treatment indications, techniques, and outcomes are described.

scholarly journals MXenes for future nanophotonic device applications

Nanophotonics ◽  
2020 ◽  
Vol 9 (7) ◽  
pp. 1831-1853
Author(s):  
Jaeho Jeon ◽  
Yajie Yang ◽  
Haeju Choi ◽  
Jin-Hong Park ◽  
Byoung Hun Lee ◽  
...  
Keyword(s):  
Solar Cells ◽  
Transition Metal ◽  
Wide Spectrum ◽  
Building Blocks ◽  
Optoelectronic Device ◽  
High Yield ◽  
Saturable Absorption ◽  
Nanophotonic Device ◽  
Wide Range ◽  
Device Applications

AbstractTwo-dimensional (2D) layers of transition metal carbides, nitrides, or carbonitrides, collectively referred to as MXenes, are considered as the new family of 2D materials for the development of functional building blocks for optoelectronic and photonic device applications. Their advantages are based on their unique and tunable electronic and optical properties, which depend on the modulation of transition metal elements or surface functional groups. In this paper, we have presented a comprehensive review of MXenes to suggest an insightful perspective on future nanophotonic and optoelectronic device applications based on advanced synthesis processes and theoretically predicted or experimentally verified material properties. Recently developed optoelectronic and photonic devices, such as photodetectors, solar cells, fiber lasers, and light-emitting diodes are summarized in this review. Wide-spectrum photodetection with high photoresponsivity, high-yield solar cells, and effective saturable absorption were achieved by exploiting different MXenes. Further, the great potential of MXenes as an electrode material is predicted with a controllable work function in a wide range (1.6–8 eV) and high conductivity (~104 S/cm), and their potential as active channel material by generating a tunable energy bandgap is likewise shown. MXene can provide new functional building blocks for future generation nanophotonic device applications.

Effects of Acoustic Excitation on a Swirling Diffusion Flame

2010 ◽  
Vol 132 (12) ◽  
Author(s):  
Michael E. Loretero ◽  
Rong F. Huang
Keyword(s):  
Flow Field ◽  
Bluff Body ◽  
Excitation Frequency ◽  
Excitation Amplitude ◽  
Mie Scattering ◽  
Flame Length ◽  
Laser Doppler Velocimeter ◽  
Scattering Method ◽  
Acoustic Excitation ◽  
Characteristic Modes

A swirling double concentric jet is commonly used for nonpremixed gas burner application for safety reasons and to improve the combustion performance. Fuel is generally spurted at the central jet while the annular coflowing air is swirled. They are normally separated by a blockage disk where the bluff-body effects further enhance the recirculation of hot gas at the reaction zone. This paper aims to experimentally investigate the behavior of flame and flow in a double concentric jet combustor when the fuel supply is acoustically driven. Laser-light sheet assisted Mie scattering method has been used to visualize the flow, while the flame lengths were measured by a conventional photography technique. The fluctuating velocity at the jet exit was measured by a two-component laser Doppler velocimeter. Flammability and stability at first fuel tube resonant frequency are reported and discussed. The evolution of flame profile with excitation level is presented and discussed, together with the reduction in flame length. The flame in the unforced reacting axisymmetric wake is classified into three characteristic modes, which are weak swirling flame, lifted flame, and transitional reattached flame. These terms reflect their primary features of flame appearances, and when the acoustic excitation is applied, the flame behaviors change with the excitation frequency and amplitude. Four additional characteristic modes are identified; e.g., at low excitation amplitudes, wrinkling flame with a blue annular film is observed because the excitation induces vortices in the central fuel jet and hence gives rise to the wrinkling of flame. The central jet vortices become larger with the increase in excitation amplitude and thus lead to a wider and shorter flame. If the excitation amplitude is increased above a certain value, the central jet vortices change the rotation direction and pacing with the annular jet vortices. These changes in the flow field induce large turbulent intensity and mixing and therefore make the flame looks blue and short. Further increase in the excitation amplitude would lift the flame because the flow field would be dramatically modified.

Numerical Characterization of Hot Gas Ingestion Through Turbine Rim Seals

2016 ◽  
Author(s):  
Riccardo Da Soghe ◽  
Cosimo Bianchini ◽  
Carl M. Sangan ◽  
James A. Scobie ◽  
Gary D. Lock
Keyword(s):  
Flow Rate ◽  
Numerical Study ◽  
Axial Flow ◽  
Radial Clearance ◽  
Buffering Effect ◽  
Hot Gas ◽  
Numerical Predictions ◽  
Wide Range ◽  
Thermal Buffering

This paper deals with a numerical study aimed at the characterization of hot gas ingestion through turbine rim seals. The numerical campaign focused on an experimental facility which models ingress through the rim seal into the upstream wheel-space of an axial-turbine stage. Single-clearance arrangements were considered in the form of axial- and radial-seal gap configurations. With the radial-seal clearance configuration, CFD steady-state solutions were able to predict the system sealing effectiveness over a wide range of coolant mass flow rates reasonably well. The greater insight of flow field provided by the computations illustrates the thermal buffering effect when ingress occurs: for a given sealing flow rate, the effectiveness on the rotor was significantly higher than that on the stator due to the axial flow of hot gases from stator to rotor caused by pumping effects. The predicted effectiveness on the rotor was compared with a theoretical model for the thermal buffering effect showing good agreement. When the axial-seal clearance arrangement is considered, the agreement between CFD and experiments worsens; the variation of sealing effectiveness with coolant flow rate calculated by means of the simulations display a distinct kink. It was found that the “kink phenomenon” can be ascribed to an over-estimation of the egress spoiling effects due to turbulence modelling limitations. Despite some weaknesses in the numerical predictions, the paper shows that CFD can be used to characterize the sealing performance of axial- and radial-clearance turbine rim seals.

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