Higher Pressure Recovery Research Articles

A Mixed-Fidelity Numerical Study for Fan–Distortion Interaction

Inlet distortion often occurs under off-design conditions when a flow separates within an intake and this unsteady phenomenon can seriously impact fan performance. Fan–distortion interaction is a highly unsteady aerodynamic process into which high-fidelity simulations can provide detailed insights. However, due to limitations on the computational resource, the use of an eddy resolving method for a fully resolved fan calculation is currently infeasible within industry. To solve this problem, a mixed-fidelity computational fluid dynamics method is proposed. This method uses the large Eddy simulation (LES) approach to resolve the turbulence associated with separation and the immersed boundary method (IBM) with smeared geometry (IBMSG) to model the fan. The method is validated by providing comparisons against the experiment on the Darmstadt Rotor, which shows a good agreement in terms of total pressure distributions. A detailed investigation is then conducted for a subsonic rotor with an annular beam-generating inlet distortion. A number of studies are performed in order to investigate the fan's influence on the distortions. A comparison to the case without a fan shows that the fan has a significant effect in reducing distortions. Three fan locations are examined which reveal that the fan nearer to the inlet tends to have a higher pressure recovery. Three beams with different heights are also tested to generate various degrees of distortion. The results indicate that the fan can suppress the distortions and that the recovery effect is proportional to the degree of inlet distortion.

New Methodology for The Determination of The Failure Times in an Ammonium Carbamate Condenser

This paper presents a new methodology to determine the optimal maintenance intervention times in the most failure prone components for an ammonium carbamate condenser. The studied condenser takes part of the process of synthesis and high-pressure recovery of synthetic urea, in a plant located in south Mexico, where the substance of the operation promotes important wear effects in industrial equipment. By implementing this methodology, we can calculate the failure times due to material wear for each individual component of de condenser, and consequently schedule specific assessment periods. For this, the minimum material thicknesses required to withstand the operating pressure are calculated according to in the American Society Mechanical Engineers (ASME,2013). The excessive maintenance expenses due to the assessment of the complete industrial equipment, can be reduced by evaluating only the necessary components that integrate the equipment, according to the determined periodicity.

Design and analysis osculating general curved cone waverider

PurposeWaverider has high lift to drag ratio and will be an idea aerodynamic configuration for hypersonic vehicles. But a structure permitting aerodynamic like waverider is still difficult to generate under airframe’s geometric constrains using traditional waverider design methods. And furthermore, traditional waverider’s aerodynamic compression ability cannot be easily adjusted to satisfy the inlet entrance requirements for hypersonic air-breathing vehicles. The purpose of this paper is to present a new method named osculating general curved cone (OCC) method aimed to improve the shortcomings of traditional waveriders.Design/methodology/approachA basic curved cone is, first, designed by the method of characteristics. Then the waverider’s inlet captured curve and front captured tube are defined in the waverider’s exit plane. Osculating planes are generated along the inlet captured curve and the designed curved cone is transformed to the osculating planes. Streamlines are traced in the transformed curved cone flow field. Combining all streamlines which have been obtained, OCC waverider’s compression surface is generated. Waverider’s upper surface uses the free stream surface.FindingsIt is found that OCC waverider has good volumetric characteristics and good flow compression abilities compared with the traditional osculating cone (OC) waverider. The volume of OCC waverider is 25 per cent larger than OC waverider at the same design condition. Furthermore, OCC waverider can compress incoming flow to required flow conditions with high total pressure recovery in the waverider’s exit plane. The flow uniformity in the waverider exit plane is quite well.Practical implicationsThe analyzed results show that the OCC waverider can be a practical high performance airframe/forebody for hypersonic vehicles. Furthermore, this novel waverider design method can be used to design a structure permitting aerodynamic like waverider for a practical hypersonic vehicle.Originality/valueThe paper puts forward a novel waverider design method which can improve the waverider’s volumetric characteristics and compression abilities compared with the traditional waverider design methods. This novel design approach can extend the waverider’s applications for designing hypersonic vehicles.

Numerical Analysis of Swirl Effects on Conical Diffuser Flows

The present paper focuses on the effect of swirl on important parameters of conical diffusers flows such as static pressure evolution, recirculation zones and wall shear stress. Governing equations are solved using a software based on the finite volume method. Moreover, turbulence effects are taken into account employing the k-e RNG model with an ennhaced wall treatment. The Reynolds number has been kept constant at 105, and various diffuser geometries were simulated, maintaining a high area ratio of 7 and varying the total divergence angle (16°, 24°, 40°, and 60°). Results showed that the swirl velocity component develops into a Rankine-vortex type or a forced-vortex type. In the former, swirl is not effective to prevent boundary layer separation, and a tailpipe is recommended to allow a large-scale mixing to enhance the pressure recovery process. In the latter case, boundary layer separation is prevented but an intermediary recirculation zone appears. Higher pressure recovery is attained at the exit of the diffuser with swirl addition, without the need of a tailpipe. Results also suggest that there is exists an imposed swirl intensity where the energy losses are minimum thus leading pressure recovery to an optimum level.

Schmale Aortenwurzel bei der Aortenklappenstenose – prognostische Implikationen

In patients with aortic stenosis a small aortic root has impact on the severity assessment as well as treatment strategy. The prognostic implications of a small aortic root were analyzed in a large prospective study of initially asymptomatic mild to moderate AS included in the Simvastatin and Ezetimibe in AS study (SEAS). A small aortic root was defined as aortic sinotubular junction diameter indexed for body size of < 1,4 cm/m in women and < 1,5 cm/m in men. A small aortic root was present in 270 patients (17,3 %) at baseline. A small aortic root was associated with larger aortic root wall thickness, higher pressure recovery, lower systemic arterial compliance and left ventricular mass index and with female sex. In patients with aortic stenosis and no evidence for cardiovascular diseases or diabetes the presence of a small aortic root was associated with higher cardiovascular events and mortality. The results suggest an association between the presence of a small aortic root and subclinical atherosclerosis.

Area Schedule Based Design of High-Pressure Recovery Radial Diffusion Systems

High-pressure ratio centrifugal compressors require advanced diffusion systems to achieve enhanced efficiencies set by future turbocharger applications. To address the shortcomings of the commonly used channel diffuser and airfoil cascade design perspectives, a streamtube based area schedule is adopted paying special attention to the diffuser entry region. It is shown that the diffusion in the semivaneless space, controlled chiefly by inlet flow angle and the vane suction side geometry, plays a key role in improving diffuser performance. Removing excess thickness from the suction side eliminates flow overspeed, increases effective diffusion length, and leads to higher pressure recovery at reduced stagnation pressure loss. The pressure side thickness distribution controls the channel area schedule. Thin leading edges (LEs) ensure smooth flow area transition into the channel and reduce the vane upstream influence, mitigating high-cycle fatigue related mechanical issues.

Small aortic root in aortic valve stenosis: clinical characteristics and prognostic implications.

In aortic valve stenosis (AS), having a small aortic root may influence both the assessment of AS severity and the treatment strategy. The aim was to test the prognostic implications of having a small aortic root in AS within a large prospective study. We used data from 4.3-year follow-up of 1560 patients with asymptomatic, initially mostly moderate AS enrolled in the Simvastatin and Ezetimibe in Aortic Stenosis study. A small aortic root was defined as inner aortic sinotubular junction diameter indexed for body height <1.4 cm/m in women and <1.5 cm/m in men. A small aortic root was found in 270 patients (17.3%) at baseline. Having a small aortic root was associated with larger aortic root wall thickness, higher pressure recovery, lower systemic arterial compliance, left ventricular mass index, and female sex in a multivariable logistic regression analysis (all P < 0.05). In the Cox regression analysis, having a small aortic root at baseline was associated with higher hazard rates of ischaemic cardiovascular events (n = 268; HR 1.55, 95% CI 1.16-2.06), non-haemorrhagic stroke (n = 55; HR 1.88, 95% CI 1.04-3.41), and cardiovascular death (n = 81; HR 2.08, 95% CI 1.28-3.39) (all P < 0.05) after adjusting for confounders, including randomized study treatment, sex, hypertension, AS severity, and aortic valve replacement. In AS patients without known cardiovascular disease or diabetes, having a small aortic root was associated with increased ischaemic cardiovascular events and mortality. The results suggest a relation between the presence of a small aortic root and that of subclinical atherosclerosis. ClinicalTrials.gov identifier: NCT00092677.

Pressure Retarded Osmosis (PRO): Past experiences, current developments, and future prospects

Pressure Retarded Osmosis (PRO) has attracted worldwide attention with respect to its salinity gradient energy production potential, and low energy desalination applications. PRO processes, which use Seawater Reverse Osmosis (SWRO) brine as draw solutions, have a higher potential of being applied to any new, and existing membrane based seawater desalination systems, as an energy production and/or conservation process. Hydraulic pressure is applied on a high salinity draw solution, and the hydraulic pressure of the high salinity draw solution can be kept relatively constant during operation, even though the volumetric flow rate is to be increased. Therefore, the draw side of the PRO process can be considered near-isobaric, in most cases. The harvested Gibbs free energy of mixing, and the volumetric expansion can explain this near-isobaric behavior of the draw side in the PRO process. Thus, PRO can be used to multiply the internal energy of the draw solution with respect to the ratio of the permeated water flux. Even though PRO has very high theoretical potential for energy production and/or recovery, there are several shortcomings, which should be answered before the realization of the scale up applications, such as; thermodynamic process optimization, high power density membranes, and high efficiency hydraulic pressure conversion and recovery systems. This review gives detailed information about the PRO process including; (1) theoretical background, (2) membranes for PRO, (3) experimental and large scale applications, and (4) economic feasibility of PRO applications.

Abstract 10031: Small Aortic Root Size Has Prognostic Implications Both for Women and Men With Asymptomatic Aortic Stenosis

Background: Sex-specific analysis of small aortic root has not been reported in asymptomatic aortic stenosis (AS) patients. Methods: We used echocardiographic and outcome data from 1560 patients with asymptomatic initially mild-moderate AS enrolled in the Simvastatin and Ezetimibe in Aortic Stenosis study. A small aortic root was defined as an inner diameter at the aortic sinotubular junction &lt; 1.5cm/m in women and &lt; 1.6cm/m in men. Results: A small aortic root was found in 17.4% patients at baseline and independently associated with higher pulse pressure/stroke volume index and aortic root wall thickness, higher pressure recovery, lower LV mass index and female sex in multivariate logistic regression analysis (all p&lt;0.05). In sex-specific multivariate Cox regression analysis, adjusting for the known prognosticators age, hypertension and AS severity and for randomized study treatment, having a small aortic root predicted a 66% higher rate of ischemic cardiovascular events and a 2-fold higher rate of non-haemorrhagic stroke and cardiovascular death (all p&lt;0.05) in men and a 2-fold higher rate of CABG in women (Table). Presence of small aortic root did not influence total mortality or aortic valve replacement in either gender. Conclusion: In asymptomatic AS patients without known cardiovascular disease or diabetes, having a small aortic root was associated with increased rate of cardiovascular events in both women and men. Table. Small aortic root as predictor of different cardiovascular events in multivariate analyses in women and men [HR (95%CI)].

The dehydration performance evaluation of a new supersonic swirling separator

A new supersonic swirling separator with an ellipsoidal central body has been designed, and an indoor experimental system and simulation method are utilised to evaluate the dehydration performance of the designed separator. The dew point depression and adaptability of the separator inlet and outlet working conditions are analysed to evaluate the dehydration performance. The experimental results show that the separator has a good dehydration performance, with the pressure recovery coefficient ranging from 20.6% to 69.8%. The maximum dew point depression is 34.9 °C, with the dew point depression decreasing as the pressure recovery coefficient increases, where the former is 18.3 °C°C at a high pressure recovery coefficient (69.8%). The inlet pressure and inlet temperature have a weak influence on the dehydration performance when the mass flow rate meets the separator working requirement. In addition, dehydration performance is not affected by the liquid outlet pressure. This means that the designed separator can operate normally across a large range of inlet and outlet working conditions.

Secondary Flows in Radial Diffusing Channels

An approximate method has been developed for the estimation of the secondary flow through a radial diffusing cascade. The basis of this numerical treatment is on the Reynolds Navier Stokes method.The theoretical development is based on the channel approach, in that the flow emerging out of the channel is assumed to consist of two sets of symmetrical vortices, which includes the shroud cross flow principle. The flow is considered to be ir-rotational and incompressible. This however is a bad approximation for high pressure recovery diffusers. The solution could be extended to compressible situations – approximate solutions only.

Effect of Convergent Angle on Flow Characteristics of Y-Shaped Diffusers Using CFD

Diffusing ducts are used in fluid flow systems, mainly in aeroplane engine inlets to decelerate the flow and to correspondingly increase the static pressure. The main problem in achieving a high pressure recovery is the flow separation which results in non-uniform distribution and excessive losses. The present work is aimed to study the flow characteristics in Y-shaped diffusing ducts. The Y-shaped diffuser has rectangular inlets and the outlet is circular with a certain settling length for the flow to be stabilized. The diffuser is modeled in CATIA V5 and further discretized using ICEMCFD12.1. Hexahedral mesh is generated for all diffuser cases, which have been used to capture the hydrodynamic boundary layers. ANSYS CFX 12.1 based on finite volume technique, using k-ε turbulence model is adopted for predicting the flow. The flow field through the 3-dimensional domain is captured by solving the appropriate governing equations namely, the continuity equation and the momentum equation. The convergence criterion is set to 10E-06 for mass and momentum. The whole investigation is done in two phases: in the first phase a commercial CFD code is validated for the results obtained for an S-shaped diffuser and in the second phase the same idea is then extended for the analysis of Y-shaped diffuser. The coefficient of static pressure, cross flow and axial flow velocity distributions are calculated based on the mass averaged quantities for the Y-shaped diffusers (30o and 40o).

Design Method for Channel Diffusers of Centrifugal Compressors

The design method for channel diffusers of centrifugal compressors, which is based on the solving of the inverse problem of gas dynamics, is presented in the paper. The concept of the design is to provide high pressure recovery of the diffuser by assuming the preseparation condition of the boundary layer along one of the channel surfaces. The channel diffuser was designed with the use of developed method to replace the vaned diffuser of the centrifugal compressor model stage. The numerical simulation of the diffusers was implemented by means of CFD software. Obtained gas dynamic characteristics of the designed diffuser were compared to the base vaned diffuser of the compressor stage.

Optimal Terminal Shock Position Under Disturbances for Ramjet Supercritical Operation

This paper presents a procedure to determine the optimal terminal shock position for a ramjet engine, balancing the conflicting requirements of high total pressure recovery and guaranteed stability in the face of disturbances. We classify and quantify the disturbances, both external and internal, that may affect the shock position in supercritical operation. This includes disturbances in the freestream and those due to flow and thermal processes in the combustion chamber. A sensitivity analysis is carried out to establish the effect of these bidirectional (from upstream and downstream) disturbances on the terminal shock position in the intake. The tip-to-tail ramjet engine model required for this purpose is sourced from the authors’ recent work. The analysis makes it possible to determine a shock position margin (supercritical margin) that simultaneously induces good engine performance and stable operation at a level of guaranteed probability.

Aerodynamic Design Investigation on Inlet-Exhaust System Using Super-Ellipse Method

Generally, the shape index n is selected in a form when design the inlet-exhaust system using traditional super-ellipse method. Unfortunately, this selection process is time-consuming and not precise enough, so the cross-section designed by super-ellipse method may get distortions easily, which influences the inner flow and the total pressure of the inlet-exhaust system greatly. Associating the shape index n with the variation pattern of the inlet-exhaust cross-section, an improved super-ellipse method is developed to design the inlet-exhaust system. This method ensures the precision and uniqueness of shape index n for any cross-section in an adaptive way. The numerical simulation results show that the S-shape inlet designed using this method has high total pressure recovery coefficient and lower distortion coefficient, the S-shaped nozzle has high total pressure recovery coefficient and thrust coefficient.

Numerical and Experimental Investigations of a Compressor Cascade Flow With Secondary Air Removal

The paper presents numerical and experimental results for a low speed compressor cascade with bleed air removal at the endwall. The aerofoil design is representative for a stator blade in a modern high pressure compressor near the casing wall. Secondary air is commonly supplied by simple bleed geometries downstream of stator rows. The focus of the present investigation was the systematic development of a passage integrated bleed configuration. With the assumption of an invariable bleed mass flow rate it should be designed to provide an advantageous effect on the main flow. Furthermore, a high pressure recovery in the bleed flow was aspired. Steady 3D RANS simulations were performed using the Spalart-Allmaras turbulence model. In both numerical simulations and experiments, an improved performance was found. Beside reduced losses and increased pressure rise, the wake flow downstream of the customized bleed geometry was found to be more homogeneous with decreased deviations due to a favorable influence on the secondary flow.

Aerodynamic Performance of a Coolant Flow Off-Take Downstream of an Outlet Guide Vane

Within the compression system of a gas turbine engine a significant amount of air is removed to fulfill various requirements associated with cooling, ventilation, and sealing. Flow is usually removed through off-takes located in regions where space is restricted, while the flow is highly complex containing blade wakes, secondary flows, and other flow features. This paper investigates the performance of a pitot style off-take aimed at providing a high pressure recovery in a relatively short length. For this to be achieved some prediffusion of the flow is required upstream of the off-take (i.e., by making the off-take larger than the captured streamtube). Although applicable to a variety of applications, the system is targeted at an intercooled aero-engine concept where the off-take would be located aft of the fan outlet guide vane (OGV) root and provide coolant flow to the heat exchangers. Measurements and numerical predictions are initially presented for a baseline configuration with no off-take present. This enabled the OGV near field region to be characterized and provided a datum, relative to which the effects of introducing an off-take could be assessed. With the off-take present a variety of configurations were investigated including different levels of prediffusion, prior to the off-take, and different off-take positions. For very compact systems of short length, such that the gap between the OGV and off-take is relatively small, the amount of prediffusion achievable is limited by the off-take pressure field and its impact on the upstream OGV row. This pressure field is also influenced by parameters such as the nondimensional off-take height and splitter thickness. The paper analyses the relative importance of these various effects in order to provide some preliminary design rules. For systems of increased length a significant amount of flow prediffusion can be achieved with little performance penalty. However, the prediffusion level is eventually limited by the increased distortion and pressure losses associated with the captured streamtube.

Control of secondary flow in a low solidity circular cascade diffuser

According to the previous experimental works on the low solidity circular cascade diffuser (LSD), a pressure recovery of a centrifugal blower was improved by the LSD significantly in a wide range of flow rate, and the pressure recovery was improved further by the LSD with a tandem cascade in comparison with the LSD with a single-row cascade. In the present study, the flow behavior in the LSD with the tandem cascade has been analyzed numerically by using the commercial CFD code of ANSYS-CFX12. It was shown clearly that the higher pressure recovery was achieved by applying the LSD with the tandem cascade, and the high pressure recovery is based on the high pressure rise in the vaneless space upstream of the LSD and the high blade loading of the front blade of the LSD. The high pressure recovery in the LSD could be achieved by controlling the flow separation on the suction surface of the front blade and also on that of the rear blade due to formation of the favorable secondary flow and due to increase in mass flow passing through the slit section between the front and rear blades.

BioDiesel as Additive in High Pressure and Temperature Steam Recovery of Heavy Oil and Bitumen

Use of additives to improve the efficiency of thermal heavy oil and bitumen recovery processes has been studied extensively over the decades. Two common types of additives used in thermal applications, mainly steam assisted recovery, are solvents and surfactants. Commercial use of solvents has setbacks due to their high costs and retrieval difficulties. Cost and stability of the surfactants under reservoir operating temperature and pressure are the major concerns. We propose the use of bioDiesel such as fatty acids methyl ester as a surfactant additive reducing heavy oil/bitumen-water interfacial tension in steam assisted recovery processes. Advantages of using bioDiesel as a surfactant additive are that bioDiesel is chemically stable under the operating pressure and temperature of the reservoir, it causes no harm on bitumen fuel quality and on release water chemistry and its use is economically feasible.We conducted a series of steam assisted bitumen recovery experiments to clarify the additional recovery potential and efficiency improvement capacity of bioDiesel. High pressure steam at 1.8 MPa pressure, 205°C was used in these tests at a 900 g/h feed rate. The porous media used was a normal grade oil sands ore obtained from a surface mine operation in Northern Alberta, Canada. Oil sands ore was packed in a basket and placed in a high pressure cell. Bitumen recovery experiments were performed by spraying canola oil fatty acid methyl ester on oil sands ore at a 2 g/kg-bitumen dosage. These tests show that bitumen recovery efficiency increases over 40%. In another series of tests, tall oil fatty acids methyl ester was injected into a high pressure steam line at a 8.3 g-bioDiesel/kg-steam dosage. Because of the solubility of bioDiesel in bitumen, the effect of bioDiesel on bitumen recovery could not be accurately concluded. Vapor pressure measurements performed on canola oil and tall oil derived bioDiesel samples suggest that saturation compositions of bioDiesel in steam at 1.8 MPa pressure and 205°C are at least one order of magnitude higher than the requested bioDiesel dosages. Further tests are planned by reducing bioDiesel dosages to about 0.5 to 1.0 g-bioDiesel/kilogram-steam and by monitoring the solubility of bioDiesel in bitumen.

Numerical simulation of natural gas flows in diffusers for supersonic separators

Diffusers play a vital role in the supersonic separator to convert kinetic energy into pressure energy. The natural gas flows in diffusers were numerically calculated using the navier-stokes equations with the RSM (reynolds stress model). The behavior of gas dynamic parameters was analyzed under conditions of shock waves and boundary layers. The results show that the conical diffuser with high pressure recovery performance is a good choice for the supersonic separator. The shock waves appear as bifurcation structures as a result of the interaction between the shocks and the boundary layer in the conical diffuser. When the swirling flow goes into the diffuser, the strength of the swirl changes the shock positions and the static pressure. The strong swirl results in the shift forward of the shock and the non-uniform distributions of the static pressure.