Numerical Evaluation of the Effects of Low Pressure EGR Mixer Configuration on Turbocharger Compressor Performance

2018 ◽  
Author(s):  
Amin Reihani ◽  
John Hoard ◽  
Stefan Klinkert ◽  
Chih-Kuang Kuan ◽  
Daniel Styles
Keyword(s):  
Flow Field ◽  
Incidence Angle ◽  
Pressure Ratio ◽  
Low Flow ◽  
Exhaust Gas ◽  
Compressor Pressure Ratio ◽  
Compressor Performance ◽  
Velocity Triangle ◽  
Induced Flow ◽  
Compressor Efficiency

Low-pressure exhaust gas recirculation (LP-EGR) is an EGR configuration in which clean exhaust gas is taken downstream of the turbine and aftertreatment, and then reintroduced upstream of the compressor (1). Employing LP-EGR on Diesel engines can improve fuel economy by reducing pumping losses, lowering intake manifold temperature and facilitating advanced combustion phasing (2, 3). The LP-EGR can also improve compressor and turbine performance by moving their operating points towards higher flow rate and higher efficiency points, which is reflected as a net reduction in pumping losses of the engine. In this study, we focus on effects of introducing LP-EGR on the compressor pressure ratio, and isentropic total-to-total efficiency. The flow field of LP-EGR and air mixing upstream of the compressor as well as the entire compressor stage were studied using a CFD RANS model. The model was validated against turbocharger gas stand measurements. A T-junction mixer was chosen as the design baseline, and various configurations of this mixer were evaluated. The impact of the geometric configuration of the mixer was studied by varying mixing length, EGR jet introduction angle, and EGR-to-air cross section area ratio over a wide range of relevant engine operating conditions. The flow field upstream of the compressor is strongly affected by the dimensionless quantity EGR-to-air momentum ratio. At intermediate momentum ratios, stream-wise counter-rotating vortex pairs (4) are induced in the flow. These vortices can reach the impeller inlet, and depending on vorticity and length scale, perturb the local velocity triangle. At low and high momentum ratios, creeping or impinging jets respectively are formed. In addition prewhirl can be induced by eccentric introduction of EGR. The EGR-induced prewhirl acts similar to an inlet guide vane and can alter the incidence angle at the impeller inlet. The performance of the compressor is altered by the EGR-induced flow field. Compressor pressure ratio is either increased or decreased depending on the direction of EGR-induced prewhirl with eccentric EGR introduction. The compressor efficiency decreases at low flow rates by introduction of concentric EGR due to perturbation of the velocity triangle at the impeller inlet. On the other hand, at low flow rates compressor efficiency can be improved by eccentric EGR introduction, which generates prewhirl in the direction of rotation of the impeller leading to improved incidence angle. The extent to which the compressor is influenced by the EGR-induced flow field is generally reduced by increasing the EGR mixing length, due to viscous damping and breakdown of large-scale EGR-induced vortices. The LP-EGR configuration provides a potential pathway towards improvement of compressor performance, not only by increasing compressor flow rate, but also by manipulation of the flow field. Given that the engine pumping losses are strongly dependent on compressor performance, specifically the compressor efficiency, this study indicates that LP-EGR provides an important path towards reducing pumping loss and improving fuel conversion efficiency.

scholarly journals Influence of Seal Cavity Leakage Flow on Compressor Performance Investigated with a Circumferentially Averaged Method

2021 ◽  
Vol 11 (2) ◽  
pp. 780
Author(s):  
Dong Liang ◽  
Xingmin Gui ◽  
Donghai Jin
Keyword(s):  
Flow Field ◽  
Pressure Ratio ◽  
Interaction Mechanism ◽  
Main Flow ◽  
Leakage Flow ◽  
Destructive Effect ◽  
Through Flow ◽  
Compressor Performance ◽  
Overall Performance ◽  
Flow Blockage

In order to investigate the effect of seal cavity leakage flow on a compressor’s performance and the interaction mechanism between the leakage flow and the main flow, a one-stage compressor with a cavity under the shrouded stator was numerically simulated using an inhouse circumferentially averaged through flow program. The leakage flow from the shrouded stator cavity was calculated simultaneously with main flow in an integrated manner. The results indicate that the seal cavity leakage flow has a significant impact on the overall performance of the compressor. For a leakage of 0.2% of incoming flow, the decrease in the total pressure ratio was 2% and the reduction of efficiency was 1.9 points. Spanwise distribution of the flow field variables of the shrouded stator shows that the leakage flow leads to an increased flow blockage near the hub, resulting in drop of stator performance, as well as a certain destructive effect on the flow field of the main passage.

An Impact of Various Shroud Bleed Slot Configurations and Cavity Vanes on Compressor Map Width and the Inducer Flow Field

2013 ◽  
Vol 135 (4) ◽  
Author(s):  
Subenuka Sivagnanasundaram ◽  
Stephen Spence ◽  
Juliana Early ◽  
Bahram Nikpour
Keyword(s):  
Flow Field ◽  
Incidence Angle ◽  
Pressure Ratio ◽  
Leading Edge ◽  
Operating Conditions ◽  
Choked Flow ◽  
Recirculating Flow ◽  
Heavy Duty Diesel ◽  
Compressor Map ◽  
The Impact

This paper describes an investigation of map width enhancement and a detailed analysis of the inducer flow field due to various bleed slot configurations and vanes in the annular cavity of a turbocharger centrifugal compressor. The compressor under investigation is used in a turbocharger application for a heavy duty diesel engine of approximately 400 hp. This investigation has been undertaken using a computational fluid dynamics (CFD) model of the full compressor stage, which includes a manual multiblock-structured grid generation method. The influence of the bleed slot flow on the inducer flow field at a range of operating conditions has been analyzed, highlighting the improvement in surge and choked flow capability. The impact of the bleed slot geometry variations and the inclusion of cavity vanes on the inlet incidence angle have been studied in detail by considering the swirl component introduced at the leading edge by the recirculating flow through the slot. Further, the overall stage efficiency and the nonuniform flow field at the inducer inlet have been also analyzed. The analysis revealed that increasing the slot width has increased the map width by about 17%. However, it has a small impact on the efficiency, due to the frictional and mixing losses. Moreover, adding vanes in the cavity improved the pressure ratio and compressor performance noticeably. A detail analysis of the compressor with cavity vanes has also been presented.

Parameter Optimization on Combined Gas Turbine-Fuel Cell Power Plants

2005 ◽  
Vol 2 (4) ◽  
pp. 268-273 ◽  
Author(s):  
Rainer Kurz
Keyword(s):  
Fuel Cell ◽  
Gas Turbine ◽  
Power Plants ◽  
Pressure Ratio ◽  
Design Parameters ◽  
Turbine Efficiency ◽  
Compressor Pressure Ratio ◽  
Turbine Design ◽  
Cycle Efficiency ◽  
Compressor Efficiency

A thermodynamic model for a gas turbine-fuel cell hybrid is created and described in the paper. The effects of gas turbine design parameters such as compressor pressure ratio, compressor efficiency, turbine efficiency, and mass flow are considered. The model allows to simulate the effects of fuel cell design parameters such as operating temperature, pressure, fuel utilization, and current density on the cycle efficiency. This paper discusses, based on a parametric study, optimum design parameters for a hybrid gas turbine. Because it is desirable to use existing gas turbine designs for the hybrids, the requirements for this hybridization are considered. Based on performance data for a typical 1600hp industrial single shaft gas turbine, a model to predict the off-design performance is developed. In the paper, two complementary studies are performed: The first study attempts to determine the range of cycle parameters that will lead to a reasonable cycle efficiency. Next, an existing gas turbine, that fits into the previously established range of parameters, will be studied in more detail. Conclusions from this paper include the feasibility of using existing gas turbine designs for the proposed cycle.

scholarly journals Meridional Considerations of the Centrifugal Compressor Development

2012 ◽  
Vol 2012 ◽  
pp. 1-11 ◽  
Author(s):  
C. Xu ◽  
R. S. Amano
Keyword(s):  
Centrifugal Compressor ◽  
High Efficiency ◽  
Pressure Ratio ◽  
Angle Distribution ◽  
High Pressure Ratio ◽  
Structure Reliability ◽  
Compressor Performance ◽  
Meridional Profile ◽  
Compressor Efficiency ◽  
Wide Operating

Centrifugal compressor developments are interested in using optimization procedures that enable compressor high efficiency and wide operating ranges. Recently, high pressure ratio and efficiency of the centrifugal compressors require impeller design to pay attention to both the blade angle distribution and the meridional profile. The geometry of the blades and the meridional profile are very important contributions of compressor performance and structure reliability. This paper presents some recent studies of meridional impacts of the compressor. Studies indicated that the meridional profiles of the impeller impact the overall compressor efficiency and pressure ratio at the same rotational speed. Proper meridional profiles can improve the compressor efficiency and increase the overall pressure ratio at the same blade back curvature.

An Impact of Various Shroud Bleed Slot Configurations and Cavity Vanes on Compressor Map Width and the Inducer Flow Field

2011 ◽  
Author(s):  
Subenuka Sivagnanasundaram ◽  
Stephen Spence ◽  
Juliana Early ◽  
Bahram Nikpour
Keyword(s):  
Flow Field ◽  
Incidence Angle ◽  
Pressure Ratio ◽  
Leading Edge ◽  
Operating Conditions ◽  
Choked Flow ◽  
Recirculating Flow ◽  
Heavy Duty Diesel ◽  
Compressor Map ◽  
The Impact

This paper describes an investigation of map width enhancement and a detailed analysis of the inducer flow field due to various bleed slot configurations and vanes in the annular cavity of a turbocharger centrifugal compressor. The compressor under investigation is used in a turbocharger application for a heavy duty diesel engine of approximately 400hp. This investigation has been undertaken using a CFD model of the full compressor stage which includes a manual multi-block structured grid generation method. The influence of the bleed slot flow on the inducer flow field at a range of operating conditions has been analysed, highlighting the improvement in surge and choked flow capability. The impact of the bleed slot geometry variations and the inclusion of cavity vanes on the inlet incidence angle have been studied in detail by considering the swirl component introduced at the leading edge by the recirculating flow through the slot. Further, the overall stage efficiency and the non-uniform flow field at the inducer inlet have been also analysed. The analysis revealed that increasing the slot width has increased the map width by about 17%. However, it has a small impact on the efficiency due to the frictional and mixing losses. Moreover, adding vanes in the cavity improved the pressure ratio and compressor performance noticeably. A detail analysis of the compressor with cavity vanes has also been presented.

Experimental Investigation of High Pressure Ratio Centrifugal Compressor With Axisymmetric and Nonaxisymmetric Recirculation Device

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Hideaki Tamaki ◽  
Xinqian Zheng ◽  
Yangjun Zhang
Keyword(s):  
High Pressure ◽  
Pressure Drop ◽  
Flow Rate ◽  
Average Distance ◽  
Pressure Ratio ◽  
Low Flow ◽  
Blade Loading ◽  
Recirculation Flow ◽  
High Pressure Ratio ◽  
Compressor Efficiency

Centrifugal compressors used for turbochargers are required to have a wide operating range. A recirculation device, which consists of a bleed slot, an upstream slot, and an annular cavity connecting both slots, is often used with them. It improves the incidence angle of the impeller leading edge, i.e., the blade loading of the inducer, at low flow rates due to the recirculation flow supplied to the compressor inlet. However, the compressor efficiency drops when there is a recirculation flow from the bleed slot to the upstream slot. A one dimensional analysis in the first section of this paper showed that the reduction in the compressor efficiency can be lowered by decreasing the pressure drop or reducing the recirculation flow rate within the recirculation device. This study examined the possibility of improvement in the compressor efficiency by the use of a recirculation device with an asymmetric bleed slot. An impeller of a turbocharger compressor is normally contained in a volute. Since the geometry of the volute is not axisymmetric, the impeller is surrounded by an asymmetric flow field. Hence each impeller passage, which is formed by two adjacent full blades, is operated at a different operating point. This means that some of the passages need the improvement in the blade loading by the recirculation device but others do not. There is a possibility that this is realized by a recirculation device with an asymmetrically distributed bleed slot, called a nonaxisymmetric recirculation device in this paper. If the asymmetric bleed slot shortens the average distance between the bleed slot and upstream slot or reduces the area of the bleed slot, it can reduce the pressure drop or recirculation flow rate within the recirculation deviceand, hence, can improve the compressor efficiency. This study discusses the characteristics of high pressure ratio compressors for turbochargers without the recirculation device and those with the recirculation device with an axisymmetric bleed slot. Furthermore, the effects of nonaxisymmetric recirculation devices on the compressor characteristics are experimentally investigated. Two types of nonaxisymmetric recirculation devices were tested. One had the bleed slot of a sine wave pattern. The other had the bleed slot partially channeled in the circumferential direction. There were appropriate positions relative to the volute for both nonaxisymmetric recirculation devices. The compressor efficiency with nonaxisymmetric recirculation devices was higher than that with axisymmetric recirculation devices and the surge lines of the compressor with nonaxisymmetric recirculation devices were located at a flow rate lower than or equal to those with the axisymmetric recirculation devices.

An Enhanced Off-Design Performance Model for Single Stage Fans

2014 ◽  
Author(s):  
Joachim Kurzke
Keyword(s):  
Flow Field ◽  
Mass Flow ◽  
Rotor Blade ◽  
Total Mass ◽  
Pressure Ratio ◽  
Fan Performance ◽  
The Core ◽  
Velocity Triangle ◽  
Tip Radius ◽  
Bypass Ratio

Modern high bypass turbofan engines have single stage fans with a low hub-tip radius ratio. The fan map is a very important element for off-design performance simulations. Such a map consists of tables with corrected mass flow, pressure ratio and efficiency for a range of corrected spool speeds. Applying the data read from a fan map to both the core and the bypass stream is inaccurate because the transonic flow field of the bypass stream is very different to the subsonic flow field of the core stream. A better approximation of reality is to use a hybrid map with total mass flow, bypass pressure ratio and efficiency. Constant factors are employed to derive the core stream pressure ratio and efficiency. For more accurate simulations two maps may be employed, one for the core and another one for the bypass stream. The total mass flow of the fan is the same in these two maps while pressure ratio and efficiency are different for the two streams. The data for each point in this so-called “Split Map” are valid for a pre-defined bypass ratio. This paper describes an alternative to the split map methodology which takes the variability of the bypass ratio into account in a different way. The hypothesis is that the overall fan performance is not affected by variations in bypass ratio. The fan performance map is completed by an additional table with core stream efficiency. This enhanced map is used as follows. When scaling the map, the bypass ratio as well as the pressure ratio and efficiencies for the core and bypass streams are known. Assumed values for fan tip speed, hub-tip radius ratio and fan inlet Mach number yield the core stream velocity triangle. The rotor blade exit flow angle from this triangle remains the same in all other operating conditions. The core flow velocity triangle analysis with known rotor blade exit angle yields the work done on the core stream during off-design. The pressure ratio is calculated from this work and the efficiency read from the core stream efficiency table mentioned above. Finally, the bypass stream pressure ratio and efficiency are calculated from the overall map and the core stream data applying the actual bypass ratio.

Variance in Compressor Turndown When Implementing Surge Control Fallback Strategies

2020 ◽  
Author(s):  
Sean W. Garceau
Keyword(s):  
Control System ◽  
Specific Gravity ◽  
Pressure Ratio ◽  
Compressor Pressure Ratio ◽  
Performance Map ◽  
Prevention System ◽  
Compressor Surge ◽  
Surge Control ◽  
Compressor Performance ◽  
Surge Protection

Abstract A centrifugal compressor surge prevention system is used to protect a compressor from surging while in operation. When using an invariant coordinate system for the compressor performance map within the surge protection system, reduced head versus reduced flow, surge control fallback strategies can be implemented within the control system to maintain operation of the compressor when instrumentation fails without placing the unit into a surge event, increasing unit availability. This paper reviews the different fallback strategies that can be implemented based on the function of the instrumentation that faulted and determine the variance between the calculated and actual turndown when different fallback strategies are active. Depending on the fallback strategy implemented, additional turndown margin may be required to ensure compressor surge is prevented by the surge prevention control system. This paper also reviews how the specific gravity, compressor pressure ratio, and compressor flow impact the variance between actual and calculated turndown when a given fallback strategy is active. Knowing the variance in the turndown allows the operator of the compressor to correctly select the desired fallback strategies and determine the needed control margin to safety operate the compressor without process disruptions. Several recommendations are outlined in the paper.

Performances and Application Perspectives of Air Heat Recovery Turbine Units

2010 ◽  
Author(s):  
Vyacheslav V. Romanov ◽  
Sergey N. Movchan ◽  
Vladimir N. Chobenko ◽  
Oleg S. Kucherenko ◽  
Valeriy V. Kuznetsov ◽  
...  
Keyword(s):  
Power Output ◽  
Gas Turbines ◽  
Heat Recovery ◽  
Pressure Ratio ◽  
Inlet Temperature ◽  
Exhaust Gas ◽  
Turbine Inlet Temperature ◽  
Compressor Pressure Ratio ◽  
Recovery System ◽  
Main Component

Adding an exhaust gas heat recovery system to a gas turbine (GT) increases its overall power output and efficiency. The introduction of an Air Heat Recovery Turbine Unit (AHRTU) using air as the heat-transfer agent is one of the ways of this increasing. This article presents the results of a GT with AHRTU for a turbine inlet temperature range from 573K to 873K and a compressor pressure ratio from 2.5 to 12. Main component performance of the AHRTU, weight and size are determined and optimized to match gas turbines. The potential for use of GT with AHRTU is specified. Exhaust gas heat recovery using a GT with AHRTU enable 4%–6% increases in efficiency (absolute), and 12%–20% increases in power output of mechanical drive plants.

Part Load Behavior of the LP Part of an Industrial Gas Turbine

2017 ◽  
Author(s):  
Milan V. Petrovic ◽  
Alexander Wiedermann ◽  
Srecko M. Nedeljkovic ◽  
Milan Banjac
Keyword(s):  
Flow Field ◽  
Gas Turbine ◽  
Incidence Angle ◽  
Pressure Ratio ◽  
Solution Procedure ◽  
Turbine Efficiency ◽  
Through Flow ◽  
Wide Range ◽  
Design Speed ◽  
Industrial Gas Turbine

The operation under off-design conditions of a two-stage LP part of a 6.5 MW industrial gas turbine was analyzed in this work. Since the turbine is able to vary the rotation speed in a wide range from 40 to 140% of the design speed, a flow with extremely large positive and negative incidence angle appears. The flow field was calculated applying 2D through-flow code for the analysis of axial multistage turbines with cooling by air from compressor bleed. The code was developed by the authors and validated by calculation of a number of test cases with different configurations. The method is based on a stream function approach and a finite element solution procedure. In parallel, the flow in the turbine was calculated using a commercial CFD code. Based on the calculated flow field, the turbine efficiency and pressure ratio and also different stage parameters were determined for the design point and for a wide range of off-design conditions. Comparison of the predicted results and measured test data for a number of parameters showed good agreement.

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