Esra Sorgüven

Exergetic efficiency of ATP production in neuronal glucose metabolism

The exergetic efficiency of ATP production in the brain is assessed using two competing models: 1) the classical model, where both neuron and the astrocyte metabolise glucose; 2) the astrocyte–neuron lactate shuttle hypothesis (ANLSH), where astrocytes metabolise glucose to lactate, then shuttle it to the neuron for aerobic respiration. Exergy analyses showed that ATP production in neuronal mitochondrion is thermodynamically much more efficient than in the cytoplasm. Comparing the Cumulative Degree of Perfection (CDP) for pyruvate production under both models showed that pyruvate production in the cytoplasm causes less exergy loss when lactate is the energy source. Therefore, we predict that the lactate shuttle model is energetically more favourable to the neuron.

Thermodynamic analysis of serogroup C antigen production by Neisseria meningitidis

Kinetic and thermodynamic models are developed to relate substrate consumption, serogroup C antigen production and growth rate of Neisseria meningitidis, a meningitides causing bacterium during the uncontrolled, pH controlled and dissolved oxygen controlled cultivation. The model shows that the microorganisms used their energy metabolism the most efficiently in the case of the guaranteed presence of the dissolved oxygen, e.g., the ultimate acceptor of the electrons in the electron transport chain. The largest heat loss per unit biomass production, the largest exergy loss per unit biomass production, and the largest entropy generation per unit biomass production are accounted in the pH controlled experiment, indicating that the growth is achieved under thermodynamically unfavourable conditions. The exergetic efficiency of the microbial production and the antigen production are not parallel, confirming the discussion accounted in the literature that the antigen is produced best under the stress conditions.

Noise prediction via large eddy simulation:Application to radial fans

In this study, aerodynamics and aeroacoustics of two radial fans are investigated by using a hybrid computational aeroacoustics method. Unsteady turbulent flow field of both fans is simulated with large eddy simulation (LES).Acoustic sources are computed based on the pressure fluctuations. Inhomogeneous wave equation, which accounts for the propagation, diffraction and scattering of the acoustic waves, is solved to determine the far field sound pressure level with the boundary element method. Numerical results are validated with experimental data. Sound pressure level distribution in narrow band frequency spectrum and directivity of the acoustic waves are predicted numerically with a high accuracy. Results of the LES provide an insight into the turbulent flow and noise generation mechanisms, which can be utilized to reduce fan noise.

Flow Simulation and Optimization of a Left Ventricular Assist Device

Artificial assist devices offer a promising treatment option for patients with congestive heart failure, especially when the patient is not eligible for heart transplantation. In order to develop a left ventricular assist device an interdisciplinary research, involving engineering and medical research teams, is conducted. The left ventricular assist device investigated in this study is the MicroMed DeBakey VAD [1], an axial blood pump that provides flow from the left ventricle to the aorta. The geometry of this baseline design is generated via parametric modeling. An optimization surface around the baseline design is formed by using the design of experiments method. Accordingly, eighty parameter sets and the corresponding CAD models are created. Flow through these pumps is simulated at the operation point. Flow data are evaluated to predict the pump performance, blood damage and bearing friction. An axial pump, closer to the optimum, is found that provides 8635 Pa pressure increase at a flow rate of 6 l/min and a rotational speed of 10000 rpm. Pressure head of the selected pump is 18% higher and blood damage is 4% less than the baseline design.Copyright

Experimental Investigation on Flows in a Corrugated Channel

Flows in a corrugated channel are investigated by a high-speed camera and a particle image velocimetry (PIV) system. The bottom wall of the rectangular channel was corrugated with periodic grooves while the top wall and two sidewalls were flat plates made of Plexiglas. Flow visualization data from the high-speed camera determine the critical Reynolds number to be around 1500 by examining the stability of the vortex in the groove as well as fluid ejection from the groove. The visualization data for turbulent flow also show how a vortex evolves within the groove and triggers another vortex formation in the subsequent groove, and how fluid ejected from the groove triggers another ejection from the subsequent groove. Thus, strong hydrodynamic interactions are observed between successive corrugations. In addition, PIV data provide the profiles of velocities and Reynolds stresses as a function of Reynolds number. Time-averaged streamlines show that a large, stable vortex exists in the groove for laminar flow. On the other hand, for turbulent flow, the vortex is unstable inside the groove, often prompting fluid ejection which interacts with the bulk flow. Especially the Reynolds stress of the square of velocity fluctuation in the direction normal to the bulk flow significantly increases as the fluid ejection from the groove intensifies with increasing Reynolds number.

Control strategies for the left ventricular assist devices

In this study numerical models for the cardiovascular system and an axial left ventricular assist device were developed and control studies have been done in the scope of a TUBITAK funded project entitled “Design, analysis, and prototype production of a miniature implantable rotary blood pump.” Diseased cardiovascular system model was obtained by adjusting the parameters of the cardiovascular system model and the rotary blood pump model was integrated to this model. At first the effects of the rotation speed of the pump was considered and then control studies have been done for the pressure difference between outlet and inlet of the pump and the pump flow.

COMPUTATIONAL NOISE PREDICTION OF A CENTRIFUGAL FAN

In this study, computational aeroacoustics methods are employed to analyze the flow and the noise emission in a centrifugal fan. Unsteady flow inside the centrifugal fan is predicted with large eddy simulation. Acoustic sources are computed based on the results of the time-dependent flow simulation. The turbulent pressure fluctuations on the blades and on the volute of the fan are used as the source terms in the acoustic analogy of Ffowcs Williams and Hawkings. Propagation, diffraction and scattering of the acoustic sources inside the volute are computed with the boundary element method. Numerically obtained sound pressure level distribution in narrow band frequency spectrum is compared with experimental measurements at certain microphone points. The numerical and experimental sound intensity maps are also compared to validate the numerical prediction of directivity. Computational results agree well with the experimental data and provide an insight of the noise emission mechanisms.Copyright

Experimental Investigation of Vortex Structure in the Corrugated Channel

Vortex structure in a corrugated channel has been studied with a PIV system measuring two-dimensional velocity fields at different locations and Reynolds numbers. The geometry of corrugation under investigation is the two-dimensional reflection of the circular cross-sectional stainless-steel flex pipe. The results show that turbulence caused by the corrugated wall affects the whole flow field in the channel even at low Reynolds number. The bulk flow field is rather chaotic in the entire channel. Moreover, the velocity vectors show significant interaction between the flow in the groove and the bulk flow. Vortex generated from the groove is very unstable and intermittent, and the vortex is not confined within the groove even at low Reynolds number. Vortex in the groove either migrates out of the groove without breaking up, or causes bursting flow from the groove to the bulk. In addition, intermittent and time-mean flow reversals are observed near the crest of the corrugation at low Reynolds number. Though the channel design is intended to be two-dimensional, flow structures in the groove appear to be three-dimensional at high Reynolds number while two-dimensional at low Reynolds number.Copyright

Computational Investigation of Vortex Structure in the Corrugated Channel

Characteristics of the flow on a corrugated wall are investigated using computational fluid dynamics. Steady and unsteady k-w simulations and large eddy simulations (LES) are performed. Results are compared with the experimental data obtained via particle image velocimetry (PIV). RANS simulations predict a coherent vortex motion, which is contained within the cavity and has little effect on the outer flow. RANS results demonstrate a mainly 2-dimensional flow and underestimate the pressure loss and friction coefficient by about 25%, compared to LES results. LES results show that the flow is highly turbulent, 3-dimensional, unsteady, and there is a strong interaction between the flow inside the corrugations and the bulk flow. Both LES and PIV represent that the separation and reattachment points vary spatially and temporally, resulting in a thick boundary layer and high friction coefficient. Sudden ejection of the flow from the cavity to the outer flow is also observed in the instantaneous snapshots taken from LES and PIV. These flow ejections prevail in the time-averaged PIV results, indicating a mean inflow towards the cavity near the side walls and a mean outflow from the cavity at the channel center. Even though instantaneous LES results show similar flow bursts, time-averaged LES results even out the inflow and outflow from the cavities, yielding no net flow in and out of the cavities.Copyright

Acoustic optimization for centrifugal fans

The aim of this study is to perform a multi-objective optimization in order to reduce the noise level of a centrifugal fan in early design stages. The main goal is to minimize the flow-induced noise while providing the required pressure rise at the operating flow rate. The design procedure begins with a baseline fan. An optimization surface around the baseline design is formed by using the design of experiments method. Accordingly, geometric parameter sets and the corresponding CAD models are generated. Flow through these fans is simulated via Reynolds averaged Navier-Stokes equations. Flow data are evaluated to predict the noise level and the fan performance. Neural network method is employed to determine the family of optimum points. Two of the Pareto designs are manufactured with rapid prototyping in order to validate the numerical optimization procedure via aerodynamic and aeroacoustic experiments. Experiments show that both designs satisfy optimization goals.