Improved Pressure Recovery Research Articles

Design and Numerical Study of Serpentine Duct using Flow Controllers for Flow Characteristics Enhancement

In the current work, computational study has been carrying out on the both baseline serpentine duct to know the flow behaviour and baseline with vortex generator to know the effect of vortex generators on the flow properties of the duct. A set of vortex generators are chosen for the study, by keeping all other parameters constant. Here in current work, for modelling the duct and vortex generator CATIA V5 is used; to discretizing the geometry ICEM CFD is used. For the analysis, the computational fluid dynamics tool FLUENT is used, SST k-ù model available in the FLUENT is used for the computations, and the results of current work will be validated with experimental results and shows that they are converged. Use of vortex generator in the current work proved extremely effective in enforcing the active flow control. Results obtained in this work are to study the pressure recovery at the engine face. The results ensure that the current work on the baseline model of serpentine inlet duct and model with vortex generator comparison is well established in case of pressure recovery and decrease in engine face distortion. After comparing the result of both baseline duct and duct with vortex generator we are expecting at least 25-35% of pressure recovery at the engine face. In the present study significant improvements characterized by an improved pressure recovery and decrease in distortion are observed over the baseline model of serpentine duct for vortex generator model. This reduction in pressure loss and distortion enhances the engine performance of thrust and also improves the overall performance of the engine.

Aerodynamic Shape Optimization of an Aircraft Propulsor Air Intake with Boundary Layer Ingestion

The growth of the airline industry has highlighted the need for more environmentally conscious aviation, leading to the conceptualization of more fuel-efficient aircraft. One concept that has received significant attention and has been associated with improved fuel efficiency is the boundary layer ingesting (BLI) propulsion system, which refers to the ingesting of the aircraft wake by the propulsors. Although BLI has theoretically been proven to reduce fuel burn, this can potentially be offset by the reduced efficiency and stability experienced by the propulsor in the presence of distorted inflow. Therefore, engine intakes must be optimized in order to mitigate the effects of BLI on the propulsion system. In this work, the shape optimization of a BLI intake is investigated using a free-form deformation technique in combination with a multi-objective genetic algorithm, in order to minimize pressure losses and distortion at the engine inlet. The optimization is performed on an S-duct intake at a cruise altitude of approximately 37,000 feet and a free stream Mach number of 0.7. An optimization strategy was developed for the task which was able to produce a Pareto optimal set of designs with improved pressure recovery and distortion. The general trend of the optimal designs shows that to reduce distortion the optimizer accelerates the flow to reduce the size of the low total pressure region and increase the dynamic pressure at the engine inlet. In contrast, the pressure recovery was increased by reducing velocity as well as shifting the maximum velocity region to the outlet, which reduces the viscous dissipation losses within the intake. The final result is a fully autonomous optimization strategy resulting in reduced pressure losses and reduced distortion leading to higher efficiency BLI S-duct intake designs.

Performance Improvement of a Mixed Flow Turbine Using 3D Blading

Abstract Mixed flow turbines have reached a level of maturity where iterative performance improvements are very small, with real performance benefits coming from better matching to a given application as opposed to improvements in technology. One ubiquitous design feature of mixed flow turbines used to control stress within the wheel is the radial fiber constraint, wherein blade material is stacked radially outward along the entirety of the blade. While this constraint yields a mechanical benefit, it constrains the aerodynamic design significantly, with the blade shape defined by one camberline. One potential means of realizing a performance improvement is the use of 3D blading, where the blade is not constrained to a radially fibered structure. In such a design, the blade shape could be freely modified to better control blade loading and secondary flows. This study investigated the viability of such 3D blading through optimization of a state of the art mixed flow turbine. An equivalent design was ensured by maintaining the meridional shape and operating conditions of the baseline (BL) wheel, thus facilitating a fair comparison between the radial and 3D wheels. The paper details the optimization including an innovative constraint-driven geometry modification tool, experimental validation of performance predictions, and an investigation into why 3D blading facilitated a performance improvement. The optimization process identified a performance improvement across the entire turbocharger operating line. With performance improvements facilitated through a reduction in tip leakage loss and improved pressure recovery within the conical diffuser. Importantly, the optimized design met targets for mass flow, maximum stress levels, and modal behavior, through the use of the novel geometry modification process.

Influence of U-tube type casing treatment on pressure fluctuations of a centrifugal pump at low flow conditions

The existence of pressure pulsations greatly increases the vibration and noise of pumps and harms their service life. In this paper, a casing treatment was employed to explore its impact on the pressure pulsations. A U-tube type groove was created at the inlet end-wall of a centrifugal pump and front cover of the impeller to connect the impeller with the inlet pipe by passing impeller leading edge. An unsteady numerical investigation was launched of the pump with and without this casing treatment, to study its influence on the pressure pulsations inside the pump and the mechanisms behind. The numerical results of the pump without casing treatment was first compared with the test performance of the pump to validate the numerical method, and gave excellent agreements with the test results. The CFD results also showed that the casing treatment increases the head coefficient and efficiency of the pump. Pressure pulsations at a reduced mass flow condition were studied by monitoring unsteady pressure signals generated by the CFD at various locations inside the pump. A Fast Fourier transform (FFT) was performed on the signals. The pump employs a double tongues volute with each tongue covering 180[Formula: see text] circumference. However, the two tongues are not identical with regard to the discharge of the pump. These geometric features of the volute and the pump’s operating condition generate several pressure pulsations in the frequencies of [Formula: see text], [Formula: see text], [Formula: see text] in the original pump. Due to the circumferential unifying capability of the casing treatment and its improvement to the impeller flow, these pulsations at impeller inlet are weakened or disappear when the U-tube is present. The pressure pulsation inside the impeller is less affected by the treatment. The [Formula: see text] pulsation at volute tongues also decreases or disappears for the same reasons, but [Formula: see text] pulsation increases slightly and this is due to the improved pressure recovery in the volute by the treatment which increases the pressure difference across one of the volute tongues. The unsteady radial force of the impeller exerting on journal bearings becomes more uniform and smaller when the casing treatment is employed.

Effect of body shape on riblets performance

By adopting a proper slip length boundary condition in Large Eddy Simulations of airfoil flows at high Reynolds numbers it can be shown that riblets reduce both friction and form drag. We show that riblets induce small but significant modifications of the pressure distribution which tends towards inviscid with improved pressure recovery in the airfoil aft. A quantitative analysis using a classical matched asymptotic expansion reveals that riblets reduce the boundary layer displacement thickness. Reduced thickening of the equivalent body introduced by the boundary layer reduces form drag leading to the unexpected improvement in pressure gradient flows measured in various experiments.

Application of laser energy deposition to improve performance for high speed intakes

Research interest has been growing in recent years in supersonic transport, particularly supersonic propulsion systems. A key component of a commonly studied propulsion system, ramjets, is the air intake. For supersonic propulsion systems a major factor in the overall efficiency is the intake pressure recovery. This refers to the ratio of the average total pressure after the intake to that of the freestream. One phenomenon that can have a large effect on this performance index is flow separation at the inlet. The aim of this work is to examine how pulsed laser energy deposition can be used to improve pressure recovery performance by reducing flow separation at the inlet. This research examines the effects of pulsed laser energy deposition upstream of an intake with an axisymmetric centrebody in a Mach 1.92 indraft wind tunnel. Laser frequency was varied between 1 and 60 kHz with an energy per pulse of 5.6 mJ. Schlieren photography was used to examine the fundamental fluid dynamics while total and static pressure downstream of the intake diffuser were measured to examine the resulting effect on the performance. Schlieren imaging shows that the interaction between the laser generated thermal bubble and the leading edge shock produced by the centrebody results in a significant reduction in separation along the intake cone. Analysis of the schlieren results and the pressure results in tandem illustrate that the average separation location along the length of the centrebody directly correlates to the pressure recovery observed in the intake. At the optimal laser frequency, found for this Mach number to be 10 kHz, the pressure recovery is found to increase by up to 4.7%. When the laser power added to the system is considered, this results in an overall increase in propulsive power of 2.47%.

Diffuser Augmented Wind Turbine (DAWT) Technologies: A Review

Diffuser Augmented Wind Turbines (DAWT) are an optimised class of wind turbines that use the theory of a Diffuser to accelerate and direct air flow onto a wind turbine rotor to drive it for higher rotations-per-minute and power output. This power output is typically measured and rated in terms of the power augmentation. Diffuser theory was pioneered in the 1970’s and has re-emerged in recent years with a range of new technological approaches to achieving laminar wind profiles, low exit pressures, improved pressure recovery, reduced blade tip losses, improved torque generation and adaptability to wind directional and speed changes. Research has been pivotal in the advancement of design and performance of DAWT’s with CFD remaining a critical analysis tool. Power augmentations have been realistically achieved within the range of 2-3 for small-medium scale turbines. In this review, ground-based Diffuser technologies have been presented primarily according to rotor type. Large-scale on-shore and off-shore concepts have been presented along with airborne technologies. Building-integrated DAWT’s are then presented with a description of some of the influential economic and technical factors that currently affect and will continue to affect the development of the DAWT industry. DAWT’s prove to have a realisable significant potential even when considered in applications across the wind turbine sector. The current DAWT industry is mostly research-based with very little commercialisation as the majority of technologies presented here are in their early developmental stages. It is expected that subsequent research and innovation in this field will be able to advance this issue to allow DAWT’s a credible chance as a key player in the wind technology sector.

An experimental and computational study of the flow pattern in a refrigerant ejector. Validation of turbulence models and real-gas effects

This investigation presents a study based on experimental and numerical flow pattern in a R134-a ejector. Furthermore, the entrainment ratio has also been analysed. The geometry of the ejector has a long tapered mixing chamber designed to improve pressure recovery. The numerical simulation is used to explain the flow features related with the static pressure profiles measurements, as well as a test case for the CFD validation. In this regard, an initial study has been undertaken in order to gain an insight into the CFD uncertainties in three relevant cases related to the ejector flow physics, namely turbulence modelling, real gas thermodynamics and shock-wave turbulent boundary layer interaction.The double-choked and mixed regime have been realized in this study. Both the standard k−ε and the SST k−ω turbulence models show good agreement between the experimental and computed pressure profiles. Regarding the entrainment ratio prediction, it was better for the latter in the double-choked regime. However, for the mixed regime, it was found that the numerical analysis could not yield a reliable entrainment ratio value using any of the turbulence models employed, although the pressure profile was accurately computed. An explanation for this contradiction has been found in this investigation. Furthermore, the numerical analysis has helped to explain the differences found between the measured pressure profiles and the one-dimensional theory prediction.

Maximizing pressure recovery using lobed nozzles in a supersonic ejector

Abstract Novel designs for supersonic ejectors in refrigeration applications focus on the reduction of the primary fluid flow rates required (entrainment ratio), as well as, increasing the total pressure recovery. This work improves the performance by enhanced mixing through flow instability by adding lobes to the circular nozzle design, combined with the profiling of the mixing channel. The objective was to determine the impact of the aspect ratio and total perimeter of the lobes on system pressure recovery and entrainment ratio. Using the conditions and geometry from the Eames [1] profiled mixing channel as the baseline and integrating a lobed nozzle, an improved pressure recovery of 6.4 from 4.0 with a perimeter value of 30 mm was achieved. Increasing the perimeter beyond this value drives the frictional losses along the wall surfaces to dominate the process and the recovered pressure reduces back to the circular nozzle.

Post‐ischaemic activation of kinases in the pre‐conditioning‐like cardioprotective effect of the platelet‐activating factor

Platelet-activating factor (PAF) triggers cardiac pre-conditioning against ischemia/reperfusion injury. The actual protection of ischaemic pre-conditioning occurs in the reperfusion phase. Therefore, we studied in this phase the kinases involved in PAF-induced pre-conditioning. Langendorff-perfused rat hearts underwent 30 min of ischaemia and 2 h of reperfusion (group 1, control). Before ischaemia, group 2 hearts were perfused for 19 min with PAF (2 x 10(-11) M); groups 3-5 hearts were co-infused during the initial 20 min of reperfusion, with the protein kinase C (PKC) inhibitor chelerythrine (5 x 10(-6) M) or the phosphoinositide 3-kinase (PI3K) inhibitor LY294002 (5 x 10(-5) M) and atractyloside (2 x 10(-5) M), a mitochondrial permeability transition pore (mPTP) opener respectively. Phosphorylation of PKCepsilon, PKB/Akappat, GSK-3beta and ERK1/2 at the beginning of reperfusion was also checked. Left ventricular pressure and infarct size were determined. PAF pre-treatment reduced infarct size (33 +/- 4% vs. 64 +/- 5% of the area at risk of control hearts) and improved pressure recovery. PAF pre-treatment enhanced the phosphorylation/activation of PKCepsilon, PKB/Akappat and the phosphorylation/inactivation of GSK-3beta at reperfusion. Effects on ERK1/2 phosphorylation were not consistent. Infarct-sparing effect and post-ischaemic functional improvement induced by PAF pre-treatment were abolished by post-ischaemic infusion of either chelerythrine, LY294002 or atractyloside. The cardioprotective effect exerted by PAF pre-treatment involves activation of PKC and PI3K in post-ischaemic phases and might be mediated by the prevention of mPTP opening in reperfusion via GSK-3beta inactivation.

Preconditioning-like cardioprotective effect of the platelet activating factor: Pre- and post-ischemic signaling pathway

We previously showed that endogenous platelet activating factor (PAF) is involved in heart preconditioning. We studied the intracellular pathways involved in PAF-induced cardioprotection. In Group 1 control hearts, Langendorff-perfused rat hearts underwent 30 min ischemia and 2 h of reperfusion. Group 2 hearts, before ischemia, were perfused for 19 min with PAF (2×10–11 M); Groups 3 and 4 hearts were co-infused with PAF and N-acetyl-l-cysteine or 5-hydroxydecanoate to scavenge ROS or to block mitochondrial-ATP-sensitive K+ (mKATP) channels, respectively. In Group 5, PAF pretreated hearts were infused during the initial 20 min of reperfusion with Atractyloside, a mitochondrial permeability transition pore (mPTP) opener. Left ventricular pressure and infarct size were determined. In sixteen additional hearts the phosphorylation of kinases by PAF was determined both in pre- and post-ischemic period. PAF-pretreatment reduced infarct size (33±4% vs 64±4.6 % of the area at risk of control hearts) and improved pressure recovery. Infarct-sparing effect of PAF was abolished by N-acetyl-l-cysteine, 5-hydroxydecanoate and Atractyloside. PAF-pretreatment enhanced the phosphorylation/activation of protein kinases (PKCB and PKB/Akt) both in the pre- and post-ischemic period, and preserved the phosphorylation/inactivation of glycogen synthase kinase-3β (GSK-3β) in reperfusion. Thus, PAF-pretreatment involves activation of mKATP channels and redox signaling in pre-ischemic phase, and PKB/Akt activation, GSK-3β inhibition and closing of mPTP in reperfusion, which explain cardioprotection.

Inverse Design of Centrifugal Compressor Vaned Diffusers in Inlet Shear Flows

A three-dimensional inverse design method in which the blade (or vane) geometry is designed for specified distributions of circulation and blade thickness is applied to the design of centrifugal compressor vaned diffusers. Two generic diffusers are designed, one with uniform inlet flow (equivalent to a conventional design) and the other with a sheared inlet flow. The inlet shear flow effects are modeled in the design method by using the so-called “Secondary Flow Approximation” in which the Bernoulli surfaces are convected by the tangentially mean inviscid flow field. The difference between the vane geometry of the uniform inlet flow and nonuniform inlet flow diffusers is found to be most significant from 50 percent chord to the trailing edge region. The flows through both diffusers are computed by using Denton’s three-dimensional inviscid Euler solver and Dawes’ three-dimensional Navier–Stokes solver under sheared in-flow conditions. The predictions indicate improved pressure recovery and internal flow field for the diffuser designed for shear inlet flow conditions.

Tests to establish flow distortion criteria for lift engines

A test program was conducted to investigate performance of lift-engine inlets and to develop a static-test device that would simulate flow distortions at the face of a lift engine. Windtunnel tests indicated that the combination of high forward speed and low engine power would cause flow separation and excessive distortion. A scoop inlet was developed that enabled the flow to turn without separation. For improved pressure recovery in static and near-static operation, longitudinal vanes in the scoop were used to augment the inlet area. By opening the vanes at low speed and closing them for engine restart, acceptable inlet performance was obtained. The wind-tunnel data showed that for a given engine-face velocity the pressure losses, both with and without scoops, were in good agreement when compared at the same approach velocity. This led to the development of a static-test distortion generator that simulated the pressure gradients measured in the wind tunnel. The distortion-generator data agree well with the wind-tunnel data, which indicated that the generator technique should be useful for engine development testing.