The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform

Dirk De Ridder - One of the best experts on this subject based on the ideXlab platform.

  • a comprehensive review of dorsomedial prefrontal cortex rtms utilizing a Double Cone coil
    Neuromodulation, 2019
    Co-Authors: Peter M Kreuzer, Dirk De Ridder, Martin Schecklmann, Jonathan Downar, Jens V Schwarzbach, Berthold Langguth
    Abstract:

    Background Repetitive transcranial magnetic stimulation (rTMS) has become increasingly popular during the last decades mainly driven by the antidepressant effects of dorsolateral prefrontal cortex stimulation with "butterfly" coils. Only recently, alternative targets such as the dorsomedial prefrontal cortex (dmPFC) have been brought into focus and innovative coil designs such as the angled geometry of the Double Cone coil (DCC) have raised hope to reach even deeper located targets. Objective To provide a systematic and comprehensive review on the application of rTMS stimulation of the dmPFC using the DCC in neuropathological and healthy samples. Methods We systematically searched the MEDLINE® database (http://www.ncbi.nlm.nih.gov/pubmed/). Due to the heterogeneous naming of DCC stimulation over the dmPFC a variety of search terms was applied resulting in a numeral quantity of 340 hits. Results DCC stimulation over the dmPFC has been proven to be safe and feasible in various neuropsychiatric disorders and in healthy subjects. Clinical results are encouraging, but have to be considered as preliminary as data from sham-controlled clinical trials and knowledge about the neurobiological underpinnings are still scarce. Conclusion DCC stimulation over the dmPFC represents a promising approach in the fast evolving noninvasive brain stimulation techniques aiming at the functional modulation of brain areas vitally involved in affect, sensory autonomic, cognitive, and salience regulation. This may hold potential for both neuroscientific research and clinical applications in the treatment of psychiatric disorders.

  • the acdc pilot trial targeting the anterior cingulate by Double Cone coil rtms for the treatment of depression
    Brain Stimulation, 2015
    Co-Authors: Peter M Kreuzer, Dirk De Ridder, Martin Schecklmann, Astrid Lehner, Thomas C Wetter, Timm B Poeppl, Rainer Rupprecht, Michael Landgrebe, Berthold Langguth
    Abstract:

    Abstract Background Repetitive transcranial magnetic stimulation (rTMS) of the dorsolateral-prefrontal cortex (DLPFC) with conventional figure-of-8 (=butterfly) coils has been used as an antidepressant therapeutic tool for almost twenty years. Very recently, an innovative rTMS coil, the so-called Double Cone coil (DC), was introduced allowing the modulation of the anterior cingulate cortex (AC). We investigated safety and therapeutic effectiveness of this stimulation in a naturalistic clinical setting. Method Forty-five patients suffering a moderate to severe depressive episode were randomized to receive 15 sessions of either conventional rTMS of the left DLPFC (" butterfly -rTMS"; 10 Hz; 2000 stimuli/day, RMT 110%), mediofrontal Double Cone coil stimulation of the anterior cingulate cortex (" ACDC -rTMS" with equal parameters), or sham-stimulation. The primary outcome was the change in the 21-items Hamilton Rating Scale for Depression (HAMD) from baseline to the end of treatment. Secondary outcome measures were changes over the course of the trial regarding the HAMD, the Beck Depression Inventory (BDI), the Clinical Global Impression (CGI) and the Global Assessment of Functioning (GAF) scales. Results There was a significant group × time interaction effect regarding the primary outcome ( F  = 3.269; df = 2,37; P  = 0.049). Post-hoc t-testing revealed a significant effect for the comparison ACDC vs. butterfly at week 3/end of treatment ( T  = 2.646; df = 26; P  = 0.014). No severe adverse events occurred during the study. ACDC -stimulation was well tolerated by the majority of patients similar like butterfly -rTMS and sham-stimulation. Conclusion This pilot study demonstrated the feasibility of ACDC -rTMS-stimulation as an add-on-treatment for depression. Its clinical effects warrant further investigation in the future.

  • tms by Double Cone coil prefrontal stimulation for medication resistant chronic depression a case report
    Neurocase, 2014
    Co-Authors: Sven Vanneste, Jan Ost, Berthold Langguth, Dirk De Ridder
    Abstract:

    A Double-Cone coil with large angled windings has been developed to modulate deeper brain areas such as the anterior cingulate cortex (ACC). Abnormal resting state activity in the pregenual ACC (pgACC), dorsal ACC (dACC) and subgenual ACC (sgACC) has been observed in depression. A patient with medication resistant chronic depression received ten sessions of transcranial magnetic stimulation (TMS) (10 Hz, 2000 stimuli/session) using a Double-Cone coil placed over the supplementary motor area, targeting the anterior cingulate. Source localized EEG recordings were conducted pre- and post-TMS. The Beck Depression Inventory (BDI-II) improved by 27%, and the two subscales of the Hospital Anxiety Depression Scale (HADS), namely depression (40%) and anxiety (33%) improved as well. Along with the clinical improvement eletrophysiological resting state activity changed in the dACC and sgACC in this patient in comparison to a normative group. The results of this case report further support the involvement of pgACC, dACC and sgACC activity in the pathophysiology of depression and indicate that modulation of neural activity in this area by high frequency TMS with a Double-Cone coil might represent a new promising approach in the treatment of medication resistant chronic depression.

  • differences between a single session and repeated sessions of 1 hz tms by Double Cone coil prefrontal stimulation for the improvement of tinnitus
    Brain Stimulation, 2013
    Co-Authors: Sven Vanneste, Dirk De Ridder
    Abstract:

    Tinnitus related distress is associated with increased activity in the anterior cingulate cortex (ACC). In a recent study, it was demonstrated that a single session of low frequency prefrontal TMS using a Double-Cone coil (DCC) modulating the ACC (AC/DC TMS, anterior cingulate cortex targeted modulation by Double-Cone coil) yields a transient improvement in subjects with chronic tinnitus. An increasing number of studies demonstrated that repeated sessions of low frequency TMS to the temporoparietal area can significantly improve tinnitus complaints. Our aim is to determine the extent to which repeated sessions of AC/DC TMS can modulate tinnitus in comparison to a single session. Seventy-three tinnitus patients received a single (N = 46) or repetitive (N = 27) session(s) of TMS using a DCC placed over the prefrontal cortex. Our results indicate that both single sessions as well as multiple sessions (i.e. 8 sessions) of AC/DC TMS suppress both tinnitus distress (respectively 7.60% vs. 26.19%) and tinnitus intensity (respectively 7.12% vs. 19.60%) transiently. It was further shown that multiple sessions of AC/DC TMS generate a higher suppression effect in comparison to a single session of AC/DC TMS and that more patients responded to repeated sessions of 1 Hz stimulation in comparison to a single session. Our findings give further support to the fact that non-auditory areas are involved in tinnitus intensity and tinnitus distress and that more patients respond to repeated sessions with a higher suppression effect in comparison to patients who received a single session, suggesting that the approach of daily TMS sessions is relevant.

  • repetitive transcranial magnetic stimulation frequency dependent tinnitus improvement by Double Cone coil prefrontal stimulation
    Journal of Neurology Neurosurgery and Psychiatry, 2011
    Co-Authors: Sven Vanneste, Mark Plazier, Paul Van De Heyning, Dirk De Ridder
    Abstract:

    Background A Double Cone coil (DCC) with large angled windings has been developed to modulate deeper brain areas such as the dorsal and subcallosal anterior cingulate cortex. Methods Seventy-eight tinnitus patients received transcranial magnetic stimulation (TMS) using a DCC placed over the dorsal frontal cortex. Treatment effects were assessed with visual analogue scale for intensity and distress. Results The results showed that 1 and 3 Hz of DCC frontal TMS can improve both tinnitus intensity and tinnitus distress, 5 Hz is equal to sham and 20 Hz is significantly worse than sham. Of the 78 tinnitus patients, 52 had no control response. Of these 52 placebo negative participants, 21 showed no suppressive response to stimulation and 31 patients were TMS responders. For this latter group, mean transient tinnitus suppression was obtained in 34.38% for tinnitus intensity and in 26% for tinnitus related distress. Conclusion Frontal TMS using a DCC is capable of suppressing tinnitus transiently dependent on the repetitive TMS frequency used. These data further support the idea that non-auditory areas are involved in tinnitus intensity and tinnitus distress modulation.

Vassilis Theofilis - One of the best experts on this subject based on the ideXlab platform.

  • on the unsteadiness of shock laminar boundary layer interactions of hypersonic flows over a Double Cone
    Physics of Fluids, 2018
    Co-Authors: Ozgur Tumuklu, Vassilis Theofilis, Deborah A Levin
    Abstract:

    Unsteadiness of axisymmetric shock-dominated hypersonic laminar separated flow over a Double Cone is studied for the first time using a combination of time accurate Direct Simulation Monte Carlo (DSMC) calculations, linear global instability analysis, and momentum potential theory (MPT). Close to steady state linear analysis reveals the spatial structure of the underlying temporally stable global modes. At all Reynolds numbers examined, the amplitude functions demonstrate the strong coupling between the separated flow region at the Cone junction with the entire shock system, including pressure and temperature waves generated behind the shock and spatially amplified Kelvin-Helmholtz waves. In addition, as the Reynolds number is increased, temporally damped harmonic shock oscillations and multiple-reflected λ-shock patterns emerge in the eigenfunctions. Application of the MPT (valid for both linear and nonlinear signals) to the highest Reynolds number DSMC results shows that large acoustic and thermal potential variations exist in the vicinity of the separation shock, the λ-shock patterns, and the shear layers. It is further shown that the motion of the bow shock system is highly affected by non-uniformities in the acoustic field. At the highest Reynolds number considered here, the unsteadiness is characterized by Strouhal numbers in the shear layer and bow-shock regions and is found to be in qualitative agreement with earlier experimental and numerical work.Unsteadiness of axisymmetric shock-dominated hypersonic laminar separated flow over a Double Cone is studied for the first time using a combination of time accurate Direct Simulation Monte Carlo (DSMC) calculations, linear global instability analysis, and momentum potential theory (MPT). Close to steady state linear analysis reveals the spatial structure of the underlying temporally stable global modes. At all Reynolds numbers examined, the amplitude functions demonstrate the strong coupling between the separated flow region at the Cone junction with the entire shock system, including pressure and temperature waves generated behind the shock and spatially amplified Kelvin-Helmholtz waves. In addition, as the Reynolds number is increased, temporally damped harmonic shock oscillations and multiple-reflected λ-shock patterns emerge in the eigenfunctions. Application of the MPT (valid for both linear and nonlinear signals) to the highest Reynolds number DSMC results shows that large acoustic and thermal poten...

  • investigation of unsteady hypersonic laminar separated flows over a Double Cone geometry using a kinetic approach
    Physics of Fluids, 2018
    Co-Authors: Ozgur Tumuklu, Deborah A Levin, Vassilis Theofilis
    Abstract:

    Shock-dominated hypersonic laminar flows over a Double Cone are investigated using time accurate direct simulation Monte Carlo combined with the residuals algorithm for unit Reynolds numbers gradually increasing from 9.35 × 104 to 3.74 × 105 m−1 at a Mach number of about 16. The main flow features, such as the strong bow-shock, location of the separation shock, the triple point, and the entire laminar separated region, show a time-dependent behavior. Although the separation shock angle is found to be similar for all Re numbers, the effects of Reynolds number on the structure and extent of the separation region are profound. As the Reynolds number is increased, larger pressure values in the under-expanded jet region due to strong shock interactions form more prominent λ-shocklets in the supersonic region between two contact surfaces. Likewise, the surface parameters, especially on the second Cone surface, show a strong dependence on the Reynolds number, with skin friction, pressure, and surface heating rates increasing and velocity slip and temperature jump values decreasing for increasing Re number. A Kelvin-Helmholtz instability arising at the shear layer results in an unsteady flow for the highest Reynolds number. These findings suggest that consideration of experimental measurement times is important when it comes to determining the steady state surface parameters even for a relatively simple Double Cone geometry at moderately large Reynolds numbers.Shock-dominated hypersonic laminar flows over a Double Cone are investigated using time accurate direct simulation Monte Carlo combined with the residuals algorithm for unit Reynolds numbers gradually increasing from 9.35 × 104 to 3.74 × 105 m−1 at a Mach number of about 16. The main flow features, such as the strong bow-shock, location of the separation shock, the triple point, and the entire laminar separated region, show a time-dependent behavior. Although the separation shock angle is found to be similar for all Re numbers, the effects of Reynolds number on the structure and extent of the separation region are profound. As the Reynolds number is increased, larger pressure values in the under-expanded jet region due to strong shock interactions form more prominent λ-shocklets in the supersonic region between two contact surfaces. Likewise, the surface parameters, especially on the second Cone surface, show a strong dependence on the Reynolds number, with skin friction, pressure, and surface heating rat...

  • investigation of unsteady hypersonic laminar separated flows over a Double Cone geometry using a kinetic approach
    Physics of Fluids, 2018
    Co-Authors: Ozgur Tumuklu, Deborah A Levin, Vassilis Theofilis
    Abstract:

    Shock-dominated hypersonic laminar flows over a Double Cone are investigated using time accurate direct simulation Monte Carlo combined with the residuals algorithm for unit Reynolds numbers gradually increasing from 9.35 × 104 to 3.74 × 105 m−1 at a Mach number of about 16. The main flow features, such as the strong bow-shock, location of the separation shock, the triple point, and the entire laminar separated region, show a time-dependent behavior. Although the separation shock angle is found to be similar for all Re numbers, the effects of Reynolds number on the structure and extent of the separation region are profound. As the Reynolds number is increased, larger pressure values in the under-expanded jet region due to strong shock interactions form more prominent λ-shocklets in the supersonic region between two contact surfaces. Likewise, the surface parameters, especially on the second Cone surface, show a strong dependence on the Reynolds number, with skin friction, pressure, and surface heating rat...

Guy M Goodwin - One of the best experts on this subject based on the ideXlab platform.

  • exploring the physiological effects of Double Cone coil tms over the medial frontal cortex on the anterior cingulate cortex an h215o pet study
    European Journal of Neuroscience, 2007
    Co-Authors: Gail Hayward, Mitul A Mehta, Catherine J Harmer, T J Spinks, Paul M Grasby, Guy M Goodwin
    Abstract:

    Transcranial magnetic stimulation (TMS) using a Double-Cone coil over the medial frontal cortex has the potential to clarify the function of the anterior cingulate cortex (ACC) in cognition, emotion and mood disorders. Following demonstration of disruption of performance on psychological tasks closely linked to cingulate function using this TMS technique, the current study aimed to directly measure the regional distribution of physiological effects of stimulation in the brain with H215O PET. Experiment 1 assessed the effect of increasing numbers of pulse trains of TMS on regional cerebral blood flow (rCBF). Experiment 2 assessed the capacity of medial frontal TMS to modulate brain activity associated with the Stroop task using medial parietal TMS as a control site of stimulation. SPM99 analyses, using the ACC as a region of interest, revealed clusters of increased rCBF during medial frontal TMS in Brodmann area 24 and reduced rCBF in more ventral ACC, the latter occurring in both experiments. In a whole-brain analysis, striking changes in rCBF were observed distal to the ACC following medial frontal TMS. Although TMS reliably affected Stroop task performance in early trials, there was no interaction between TMS and Stroop condition in rCBF. Our results suggest that medial frontal TMS using the Double-Cone coil can affect ACC activity. However, a number of more distal cortical areas were also affected in these experiments. These additional changes may reflect either 'downstream' effects of altered cingulate cortex activity or direct effects of the coil. © The Authors (2007).

  • exploring the physiological effects of Double Cone coil tms over the medial frontal cortex on the anterior cingulate cortex an h2 15 o pet study
    European Journal of Neuroscience, 2007
    Co-Authors: Gail Hayward, Mitul A Mehta, Catherine J Harmer, T J Spinks, Paul M Grasby, Guy M Goodwin
    Abstract:

    Transcranial magnetic stimulation (TMS) using a Double-Cone coil over the medial frontal cortex has the potential to clarify the function of the anterior cingulate cortex (ACC) in cognition, emotion and mood disorders. Following demonstration of disruption of performance on psychological tasks closely linked to cingulate function using this TMS technique, the current study aimed to directly measure the regional distribution of physiological effects of stimulation in the brain with H2(15)O PET. Experiment 1 assessed the effect of increasing numbers of pulse trains of TMS on regional cerebral blood flow (rCBF). Experiment 2 assessed the capacity of medial frontal TMS to modulate brain activity associated with the Stroop task using medial parietal TMS as a control site of stimulation. SPM99 analyses, using the ACC as a region of interest, revealed clusters of increased rCBF during medial frontal TMS in Brodmann area 24 and reduced rCBF in more ventral ACC, the latter occurring in both experiments. In a whole-brain analysis, striking changes in rCBF were observed distal to the ACC following medial frontal TMS. Although TMS reliably affected Stroop task performance in early trials, there was no interaction between TMS and Stroop condition in rCBF. Our results suggest that medial frontal TMS using the Double-Cone coil can affect ACC activity. However, a number of more distal cortical areas were also affected in these experiments. These additional changes may reflect either 'downstream' effects of altered cingulate cortex activity or direct effects of the coil.

Andrew T Conn - One of the best experts on this subject based on the ideXlab platform.

  • power optimization of a conical dielectric elastomer actuator for resonant robotic systems
    Extreme Mechanics Letters, 2020
    Co-Authors: Chongjing Cao, Andrew T Conn, Xing Gao, Stuart C Burgess
    Abstract:

    Abstract Insects utilize resonant actuation to amplify the flapping stroke and improve the energy efficiency. The inherent elasticity in dielectric elastomer actuators (DEAs) offers the advantage over conventional actuators of achieving resonant actuations with no additional elastic elements required. Despite that the resonant actuation of the DEAs have attracted great research interests, no optimization has been done on the output performance of resonating DEAs. In this work, a Double Cone DEA (DCDEA) configuration is adopted and a numerical model is developed to characterize its dynamic response. An effective power study framework is developed and the power output of the DCDEA is optimized against its pre-stretch ratios and spacer length. To demonstrate the potential exploitation of resonant DEA performance, a bioinspired flapping wing mechanism driven by the optimized DCDEA design is developed with a peak flapping stroke of 31°at its resonance of 30 Hz.

  • a compliantly coupled dielectric elastomer actuator using magnetic repulsion
    Applied Physics Letters, 2019
    Co-Authors: Chongjing Cao, Xing Gao, Andrew T Conn
    Abstract:

    Dielectric elastomer actuators (DEAs) have attracted growing research interest over the past two decades for their large actuation strain, inherent compliance, and low cost. The conical DEA configuration is particularly attractive thanks to their simple structure and high force/stroke actuation. A Double Cone DEA design with two antagonistic membranes allows active bidirectional actuation. However, in existing Double Cone DEA designs, the two membranes are rigidly coupled, which restricts their relative actuation response under periodic electrical input to 180° out-of-phase operation. This work presents a magnetically coupled DEA with compliant coupling by a magnetic repulsion. The compliant coupling allows two separate inputs with a fully adjustable phase difference. The current prototype demonstrates a peak normalized stroke of 14% (relative to the nominal DEA height) at a phase shift of 180° and a normalized linear expansion between the two membranes of up to 8.3% (relative to the nominal DEA height) at a phase shift of 0° at 0.5 Hz. This results in several emerging actuation behaviors, which could potentially be suitable for controllable shape changing actuations, active vibration damping, and bioinspired locomotion.

  • performance optimization of a conical dielectric elastomer actuator
    Actuators, 2018
    Co-Authors: Chongjing Cao, Andrew T Conn
    Abstract:

    Dielectric elastomer actuators (DEAs) are known as ‘artificial muscles’ due to their large actuation strain, high energy density and self-sensing capability. The conical configuration has been widely adopted in DEA applications such as bio-inspired locomotion and micropumps for its good compactness, ease for fabrication and large actuation stroke. However, the conical protrusion of the DEA membrane is characterized by inhomogeneous stresses, which complicate their design. In this work, we present an analytical model-based optimization for conical DEAs with the three biasing elements: (I) linear compression spring; (II) biasing mass; and (III) antagonistic Double-Cone DEA. The optimization is to find the maximum stroke and work output of a conical DEA by tuning its geometry (inner disk to outer frame radius ratio a/b) and pre-stretch ratio. The results show that (a) for all three cases, stroke and work output are maximum for a pre-stretch ratio of 1 × 1 for the Parker siliCone elastomer, which suggests the stretch caused by out-of-plane deformation is sufficient for this specific elastomer. (b) Stroke maximization is obtained for a lower a/b ratio while a larger a/b ratio is required to maximize work output, but the optimal a/b ratio is less than 0.3 in all three cases. (c) The Double-Cone configuration has the largest stroke while single Cone with a biasing mass has the highest work output.

Ozgur Tumuklu - One of the best experts on this subject based on the ideXlab platform.

  • on the unsteadiness of shock laminar boundary layer interactions of hypersonic flows over a Double Cone
    Physics of Fluids, 2018
    Co-Authors: Ozgur Tumuklu, Vassilis Theofilis, Deborah A Levin
    Abstract:

    Unsteadiness of axisymmetric shock-dominated hypersonic laminar separated flow over a Double Cone is studied for the first time using a combination of time accurate Direct Simulation Monte Carlo (DSMC) calculations, linear global instability analysis, and momentum potential theory (MPT). Close to steady state linear analysis reveals the spatial structure of the underlying temporally stable global modes. At all Reynolds numbers examined, the amplitude functions demonstrate the strong coupling between the separated flow region at the Cone junction with the entire shock system, including pressure and temperature waves generated behind the shock and spatially amplified Kelvin-Helmholtz waves. In addition, as the Reynolds number is increased, temporally damped harmonic shock oscillations and multiple-reflected λ-shock patterns emerge in the eigenfunctions. Application of the MPT (valid for both linear and nonlinear signals) to the highest Reynolds number DSMC results shows that large acoustic and thermal potential variations exist in the vicinity of the separation shock, the λ-shock patterns, and the shear layers. It is further shown that the motion of the bow shock system is highly affected by non-uniformities in the acoustic field. At the highest Reynolds number considered here, the unsteadiness is characterized by Strouhal numbers in the shear layer and bow-shock regions and is found to be in qualitative agreement with earlier experimental and numerical work.Unsteadiness of axisymmetric shock-dominated hypersonic laminar separated flow over a Double Cone is studied for the first time using a combination of time accurate Direct Simulation Monte Carlo (DSMC) calculations, linear global instability analysis, and momentum potential theory (MPT). Close to steady state linear analysis reveals the spatial structure of the underlying temporally stable global modes. At all Reynolds numbers examined, the amplitude functions demonstrate the strong coupling between the separated flow region at the Cone junction with the entire shock system, including pressure and temperature waves generated behind the shock and spatially amplified Kelvin-Helmholtz waves. In addition, as the Reynolds number is increased, temporally damped harmonic shock oscillations and multiple-reflected λ-shock patterns emerge in the eigenfunctions. Application of the MPT (valid for both linear and nonlinear signals) to the highest Reynolds number DSMC results shows that large acoustic and thermal poten...

  • investigation of unsteady hypersonic laminar separated flows over a Double Cone geometry using a kinetic approach
    Physics of Fluids, 2018
    Co-Authors: Ozgur Tumuklu, Deborah A Levin, Vassilis Theofilis
    Abstract:

    Shock-dominated hypersonic laminar flows over a Double Cone are investigated using time accurate direct simulation Monte Carlo combined with the residuals algorithm for unit Reynolds numbers gradually increasing from 9.35 × 104 to 3.74 × 105 m−1 at a Mach number of about 16. The main flow features, such as the strong bow-shock, location of the separation shock, the triple point, and the entire laminar separated region, show a time-dependent behavior. Although the separation shock angle is found to be similar for all Re numbers, the effects of Reynolds number on the structure and extent of the separation region are profound. As the Reynolds number is increased, larger pressure values in the under-expanded jet region due to strong shock interactions form more prominent λ-shocklets in the supersonic region between two contact surfaces. Likewise, the surface parameters, especially on the second Cone surface, show a strong dependence on the Reynolds number, with skin friction, pressure, and surface heating rates increasing and velocity slip and temperature jump values decreasing for increasing Re number. A Kelvin-Helmholtz instability arising at the shear layer results in an unsteady flow for the highest Reynolds number. These findings suggest that consideration of experimental measurement times is important when it comes to determining the steady state surface parameters even for a relatively simple Double Cone geometry at moderately large Reynolds numbers.Shock-dominated hypersonic laminar flows over a Double Cone are investigated using time accurate direct simulation Monte Carlo combined with the residuals algorithm for unit Reynolds numbers gradually increasing from 9.35 × 104 to 3.74 × 105 m−1 at a Mach number of about 16. The main flow features, such as the strong bow-shock, location of the separation shock, the triple point, and the entire laminar separated region, show a time-dependent behavior. Although the separation shock angle is found to be similar for all Re numbers, the effects of Reynolds number on the structure and extent of the separation region are profound. As the Reynolds number is increased, larger pressure values in the under-expanded jet region due to strong shock interactions form more prominent λ-shocklets in the supersonic region between two contact surfaces. Likewise, the surface parameters, especially on the second Cone surface, show a strong dependence on the Reynolds number, with skin friction, pressure, and surface heating rat...

  • investigation of unsteady hypersonic laminar separated flows over a Double Cone geometry using a kinetic approach
    Physics of Fluids, 2018
    Co-Authors: Ozgur Tumuklu, Deborah A Levin, Vassilis Theofilis
    Abstract:

    Shock-dominated hypersonic laminar flows over a Double Cone are investigated using time accurate direct simulation Monte Carlo combined with the residuals algorithm for unit Reynolds numbers gradually increasing from 9.35 × 104 to 3.74 × 105 m−1 at a Mach number of about 16. The main flow features, such as the strong bow-shock, location of the separation shock, the triple point, and the entire laminar separated region, show a time-dependent behavior. Although the separation shock angle is found to be similar for all Re numbers, the effects of Reynolds number on the structure and extent of the separation region are profound. As the Reynolds number is increased, larger pressure values in the under-expanded jet region due to strong shock interactions form more prominent λ-shocklets in the supersonic region between two contact surfaces. Likewise, the surface parameters, especially on the second Cone surface, show a strong dependence on the Reynolds number, with skin friction, pressure, and surface heating rat...