• Journal of Mechanical Science and Technology
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• v.16 no.8
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• pp.1144-1153
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• 2002

A hybrid performance prediction method is proposed in the present study. A channel diffuser is divided into four subregions: vaneless space, semi-vaneless space, channel, and channel exit region. One-dimensional compressible core flow and boundary layer calculation of each region with an incidence loss model and empirical correlation of residuary pressure recovery coefficient of a channel predict the performance of diffusers. Three channel diffusers are designed and tested for validating the developed prediction method. The pressure distributions from an impeller exit to the channel diffuser exit are measured and discussed for various operating conditions from choke to nearly surge conditions. The strong non-uniform pressure distribution which is caused by impeller-diffuser interaction is obtained over the vaneless and semi-vaneless spaces. The predicted performance shows good agreement with the measured performance of diffusers at a design condition as well as at off-design conditions.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.1
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• pp.419-425
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• 2019

The objective of this study was to investigate the cooling performance characteristics of a hybrid refrigeration system in a heavy duty vehicle. The tested hybrid refrigeration system had additionally an electric compressor besides the present mechanical compressor for selective use according to the operating conditions. The applied electric compressor was a scroll type and with 18.0 cc displacement. In order to analyze the performance characteristics of the hybrid refrigeration system with respect to the cooling capacity and Coefficient of Performance (COP), other components, including two different types of compressors, were installed and tested under various operating conditions such as compressor speed and air flow rate of the evaporator. When the electric compressor was operated at 4,500 rev/min, the cooling capacity was about 4.0kW and COP was 3.5. When the mechanical compressor was operated, whereas the cooling capacity was higher than the electric controlled compressor, COP was lower due to the larger displacement and higher power consumption. To analyze the hybrid system operating characteristics due to reasonable cooling capacity with electric compressor operation, the mechanical compressor and electric compressor were operated by turns every 10 minutes under certain system operating conditions. Because surge pressure occurred when both compressors were switched on, the operating strategy required some time to balance the system pressure.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2005.11a
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• pp.299-303
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• 2005

In the present study, in order to improve precision of the component characteristic maps generated by the scaling method, a map generation method which can produce a compressor map from some experimental performance data using GAs(Genetic Algorithms) was proposed. However, in case of the proposed map generation method only using GAs, because it has a drawback for estimating correctly the surge points and the choke points of the compressor map, a modified GAs method was additionally proposed through complementally use of the scaling method to determine obviously those points of the compressor map.

• Journal of the Korean Society of Propulsion Engineers
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• v.16 no.4
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• pp.23-32
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• 2012

The present study is aimed to develop an integrated performance analysis approach for the application of a compressor with variable inlet guide vane (VIGV) and vairable stator vane (VSV) in a small turbofan engine. For the integrated analysis approach, an engine performance analysis program, NPSS and a computer program used for predicting of axial flow compressor performance based on stage stacking method, STGSTK were linked with an optimisation package, Isight. This enables off-design performance analysis for the turbofan engine with VIGV and VSV hence provides the capability to predict stable operation condition of the engine with acceptable surge margin.

• Journal of Power System Engineering
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• v.3 no.3
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• pp.60-69
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• 1999

The noise and vibration sources of rotary compressor for room air-conditioner are pressure pulsation of compression process, cavity resonance of inner space, structural radiation noise of shell and impact noise of discharge valve. Among them, pressure pulsation is very important noise and vibration source. Because it transferred various kinds of noise and vibration like as mentioned above. In this reason, muffler and resonator are used in order to absorb and remove these noises. But an analytical prediction using acoustic analysis does not coincident with the experimental result. The difference between analysis and actual state is due to the assumption of analysis. This paper covered with new concept of muffler design based on the turbulence kinetic energy of flow by using CFD. From this analysis, it is possible to decide the best position of discharge port of muffler. Therefore $2{\sim}3dB$ noise reduction effect is acquired in rotary compressor of 5000 BTU grade. Also new approach of resonator design is suggested. From this study, the characteristics of resonator and surge hole (a kind of resonator without pipe length) are identified. The former is useful for pure tone noise (narrow frequency band), and the latter is effective for broad frequency band. This paper shows that it is very available to use 3 dimensional analysis of resonator in order to predict more exact tuning frequency. The result is proved by a lot of experiments. From combination of fluid analysis and acoustic analysis, up stream position is effective location of resonator concerning turbulence motion of fluid.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.11
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• pp.1015-1022
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• 2013

This study simulates the operation of a 200 kW class micro gas turbine that is currently under development. The performance and operating characteristics depending on the load control scheme (constant turbine inlet temperature versus constant turbine exit temperature) and ambient condition were investigated using detailed component performance data. The sensitivities of operating parameters, such as the compressor surge margin and flow path temperatures, according to unit fuel flow change were predicted for a wide load range. The sensitivity analysis showed that the steady state calculation provided useful information about the maximum surge margin reduction during load change.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2913-2917
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• 2007

Turbocharger has been widely used in many passenger cars in application with diesel engines because of high power and fuel efficiency. However, flow-induced noise (whoosh or hissing noise) which is generated within the compressor during its operation at marginal surge line can deteriorate noise characteristics. Hissing noise excitation was associated with the generation of turbulence within the turbocharger compressor and radiated through the transmission path in turbocharger system. In this study, a sharp-edged reactive-type muffler was devised and installed in the transmission path to reduce the hissing noise. Acoustic and fluid dynamic characteristics for the muffler were investigated which is related to the unsteadiness of turbulence and pressure in turbocharger system. A transfer matrix method was used to analyze the transmission loss of the muffler. Simple expansion muffler with extended tube of the reactive type is proposed for the reduction of high frequency component noise. Turbulence computation was carried out by a standard ${\kappa}-{\varepsilon}$ model. An optimal design condition of the muffler was obtained by extensive acoustic and fluid dynamic analysis on the engine dynamometer with anechoic chamber. A significant reduction of the hissing noise was achieved at the optimal design of the muffler as compared with the conventional turbocharger system.

• Journal of computational fluids engineering
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• v.10 no.1
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• pp.51-55
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• 2005

For proper installation, operation and performance of axial flow jet engines in aircrafts, the impacts and effects of inlet flow distortion in axial compressors have to be understood. Inlet distortion conditions may cause component-mismatch and instability problems known as rotating stall, and severe oscillations of mass flow rate called surge or a combination of both. Typical effects of this phenomenon include stresses and wear on the compressor blading, destruction of entire jet engines due to the failure of airfoil and mechanical failure or interruption of the combustion process. Therefore, it is important to study inlet flow distortion and its propagation effects to minimize and hence to prevent the occurrence of such calamity. The current novel integral method with parametric analysis signifies its validity to this field of research and offers much potential for further improvements. The present effort further indicates that this simple method may be flourishing in the problems of strongly distorted flow and propagating stall in axial compressor. It is therefore believe that using a more realistic and flexible velocity and pressure profiles could develop this approach further.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.2
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• pp.79-84
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• 2009

Turbocharger has been widely used in many passenger cars in application with diesel engines because of high power and fuel efficiency. However, flow-induced noise (whoosh or hissing noise) which is generated within a compressor during its operation at marginal surge line can deteriorate noise characteristics. Hissing noise excitation is associated with the generation of turbulence within the turbocharger compressor and radiated through the transmission path in a turbocharger system. In this study, a expansion muffler with lids is devised and installed in the transmission path to reduce the hissing noise. Acoustic and fluid dynamic characteristics for the muffler are investigated which are related to the unsteadiness of turbulence and pressure in the turbocharger system. A transfer matrix method is used to analyze the transmission loss of the muffler. A simple expansion muffler with lids is proposed for the reduction of high frequency component noise. Turbulence simulation is carried out by a standard k - ${\varepsilon}$ model. An optimal design condition of the muffler is obtained by extensive acoustic and fluid dynamic analysis on the engine dynamometer with anechoic chamber. A significant reduction of the hissing noise is achieved at the optimal design of the muffler as compared with the conventional muffler.

• Advances in aircraft and spacecraft science
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• v.5 no.3
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• pp.349-362
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• 2018

A non-linear numerical simulation technique for predicting the unsteady performances of an airbreathing engine is developed. The study focuses on the simulation of integrated propulsion systems, where a closer coupling is needed between the airframe and the engine dynamics. In fact, the solution of the fully unsteady flow governing equations, rather than a lumped volume gas dynamics discretization, is essential for modeling the coupling between aero-servoelastic modes and engine dynamics in highly integrated propulsion systems. This consideration holds for any propulsion system when a full separation between the fluid dynamic time-scale and engine transient cannot be appreciated, as in the case of flow instabilities (e.g., rotating stall, surge, inlet unstart), or in case of sudden external perturbations (e.g., gas ingestion). Simulations of the coupling between external and internal flow are performed. The flow around the nacelle and inside the engine ducts (i.e., air intakes, nozzles) is solved by CFD computations, whereas the flow evolution through compressor and turbine bladings is simulated by actuator disks. Shaft work balance and rotor dynamics are deduced from the estimated torque on each turbine/compressor blade row.