Performance and efficiency analysis of a centrifugal compressor under pulsating flow
File(s)
Author(s)
Parikh, Aakeen
Type
Thesis
Abstract
The performance of a turbocharger centrifugal compressor is affected by the engine system in which it operates. This type of turbomachine experiences a pulsating backpressure caused by the opening and closing of the engine intake valves. This research studies the impact of these pulsating conditions on the behaviour of a centrifugal compressor and presents modifications to compressor designs to improve performance.
This research is conducted experimentally and computationally. The experimental facility is improved for increased accuracy in measurements and a prototype torque meter has also been developed to enable high speed measurements of compressor torque. The experimental results show that in pulsating conditions the largest drop in compressor efficiency (around 4% compared to steady conditions) takes place in the large mass flow rate conditions, as the fluctuating high-pressure amplitudes at the compressor exit lead to increased losses in the volute.
Computational investigation of the near surge operating point shows that, in pulsating flow, instantaneous changes in pressure allows the flow field near the impeller to stabilise despite low mass flow conditions that would otherwise trigger surge, resulting in the key benefit of extended operating range in low flow conditions. Further detailed computational assessments of the compressor model show that the volute and volute tongue regions are affected under pulsating flow. The volute tongue contributes to 20% of the losses on average in pulsating states.
Initial results from two compressor design modifications show an improved compressor performance, with efficiency improvement of 2% with a sharp tongue modification. This is a significant outcome from this research and has an influence on the design of turbochargers, as this improvement could indirectly impact the efficiency of the entire engine system. This would lead to greater fuel economy and reduced emissions from transport, which is necessary to address global climate change.
This research is conducted experimentally and computationally. The experimental facility is improved for increased accuracy in measurements and a prototype torque meter has also been developed to enable high speed measurements of compressor torque. The experimental results show that in pulsating conditions the largest drop in compressor efficiency (around 4% compared to steady conditions) takes place in the large mass flow rate conditions, as the fluctuating high-pressure amplitudes at the compressor exit lead to increased losses in the volute.
Computational investigation of the near surge operating point shows that, in pulsating flow, instantaneous changes in pressure allows the flow field near the impeller to stabilise despite low mass flow conditions that would otherwise trigger surge, resulting in the key benefit of extended operating range in low flow conditions. Further detailed computational assessments of the compressor model show that the volute and volute tongue regions are affected under pulsating flow. The volute tongue contributes to 20% of the losses on average in pulsating states.
Initial results from two compressor design modifications show an improved compressor performance, with efficiency improvement of 2% with a sharp tongue modification. This is a significant outcome from this research and has an influence on the design of turbochargers, as this improvement could indirectly impact the efficiency of the entire engine system. This would lead to greater fuel economy and reduced emissions from transport, which is necessary to address global climate change.
Version
Open Access
Date Issued
2023-08-02
Date Awarded
2024-03-01
Copyright Statement
Creative Commons Attribution NonCommercial Licence
License URL
Advisor
Barrera-Medrano, Maria Esperanza
Martinez-Botas, Ricardo
Sponsor
Mitsubishi Heavy Industries (Firm)
Engineering and Physical Sciences Research Council
Grant Number
EPSRC DTP 2018-2019 training grant (EP/R513052/1)
Publisher Department
Mechanical Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)