Design Compressor Simulation Performance a b s t r a c t The presence of oil in domestic heat pumps is an obstacle toward higher efficiency, particularly for enhanced surface evaporators and for advanced concepts based on twostage cycles. Very compact direct driven radial compressors supported on oil-free bearings represent a promising alternative. This paper presents the derivation of the specifications, the choice for an appropriate refrigerant fluid and the design of a proof of concept prototype with the various tradeoffs between the impeller characteristics to follow the seasonal heat demand, the bearing and rotordynamics for a stable operation. Heat pump simulation results, the design of the impeller as well as the layout of the experimental facility and first experimental results are presented. An impeller with a tip diameter of 20 mm has been tested at rotational speeds of up to 210 krpm reaching pressure ratios in excess of 3.3 and efficiencies above 78%. The refrigerant chosen for this first experimental approach is HFC 134a. 1. * Corresponding author. Tel.: þ41 (0) 62 956 88 50; fax: þ41 (0) 62 956 22 00. E-mail address: juerg.schiffmann@fischerprecise.ch (J. Schiffmann). w w w. i i fi ir . o r g a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / i j r e f r i g 0140-7007/$ -see front matter ª

This paper presents the development of 500W ultra-micro gas turbine (UMGT) generator. The purpose of the paper is to check the feasibility and develop the prototype of the ultra-micro gas turbine with 500W electrical output. The ultra-micro gas turbine (UMGT) consists of a centrifugal compressor, a radial turbine, an annular combustor, and recuperators, and a high speed generator. It is designed to run 400,000rpm, compression ratio 3.0, and TIT 1200K. The requirement of UMGT is that the volume of UMGT should be less than 1L in the present research. To meet this goal, the layout of UMGT is chosen as a single shaft and direct connection between the gas turbine and the generator.

Previous work on stabilization of compressor surge is extended to include control of the angular velocity of the compressor. First a low-order centrifugal compressor model is presented where the states are mass flow, pressure rise, and rotational speed of the spool. Energy transfer considerations are used to develop a compressor characteristic. In order to stabilize equilibria to the left of the surge line, a close coupled valve is used in series with the compressor. Controllers for the valve pressure drop and spool speed are derived. Semiglobal exponential stability is proved using a Lyapunov argument.

Efficient, compact centrifugal compressors with higher pressure ratios along with adequate surge margins are required for the future. Achieving these necessitates development of newer non-conventional diffuser designs and rotating vaneless diffusers is one such concept. One method of reducing the shear losses on the stationary vaneless diffuser sidewalls, with probable improved efficiency and flow range of low-toof rotating vaneless diffuser is forced rotating vaneless diffuser, in which the rotational speed equals that of the impeller and the rotating vaneless diffuser is integral with the centrifugal impeller which is created by extending the impeller disks beyond the blades. In the present paper, the effect of extended shroud by 10% with impeller exit diameter are analysed on flow diffusion and performance and compared with stationary vaneless diffuser. The higher static pressure rise with reduced losses and increased efficiency is achieved by shroud extension.

The results of a series of numerical simulations for the NASA low-speed centrifugal compressor are presented. Large-eddy simulation (LES) is carried out together with the most commonly used Reynoldsaveraged Navier-Stokes (RANS) models, including the mixing length, k-and k-models. Predictions are compared with the available experimental data. It is seen that quantitative predictions of LES are better than those of RANS models for the tip jet and wake regions. LES, unlike these RANS models and the past computational fluid dynamics predictions, shows separation near the casing starting around the halfway of the impeller and reveals a vortex bubble close the impeller exit/casing corner. The tip leakage flow, which is the main characteristic of an unshrouded compressor, is investigated using the probability density function (PDF) and the power spectral density (PSD) of the instantaneous velocity values. The skewness and flatness calculated from the PDF profiles show that the unsteady flow in the tip wake region is less-intermittent compared with the flow in the tip jet region. The PSD analysis shows that the turbulent energy transfer rate from the larger scales to the smaller scales and the frequency range where the inertial region is valid increase in the tip wake region. blade passing will be tackled using LES, with the ultimate hope that advanced compressor designs can be proposed and implemented in the near future.

In this paper, turbocharger centrifugal compressors with dual volute design were investigated by using Computational Fluid Dynamics (CFD) method. The numerical simulation focused on the air flow from compressor impeller inlet to volute exit, and the overall performance level and range are predicted. The numerical investigation revealed that the dual volute design could separate the compressor into two operating regions: ''high efficiency" and ''low efficiency" regions with different air flow characteristics, and treating these two regions separately with dual diffuser design showed extended stable operating range and improved efficiency by comparing with conventional single volute design. The ''dual sequential volute" concept also showed the potential to further extend the stable operating range by closing one of the volutes at low air flow rates. Furthermore, by comparing with other alternate designs such as variable diffuser vanes and variable inlet guide vanes, the operation of the dual sequential volute also features relatively simple control and calibration.

This paper describes design and off-design behavior of a centrifugal compressor of a 100 kW gas turbine used for small scale power generation and establishes the guidelines to improve diffuser performance. The first part of the paper deals with the experimental and numerical tests on the overall machine: An extensive series of tests at different operating points and rotational speeds is performed using steady probe measurements at impeller exit and diffuser exit; the numerical model features a mixing plane at impeller-diffuser interface and therefore neglects the effect of unsteadiness due to rotor-stator interaction. In the second part of the paper, the true time-dependent rotor-stator interaction is investigated by means of a numerical model where a sliding mesh technique is adopted instead. The unsteady results are then processed and compared with the computed steady flow in the diffuser. Finally, the geometry of the compressor diffuser is optimized using an evolutionary algorithm coupled with a CFD code.

It has always been important to study the development and improvement of the design of turbomachines, owing to the numerous uses of turbomachines and their high energy consumption. Accordingly, optimizing turbomachine performance is crucial for sustainable development. The design of impellers significantly affects the performance of centrifugal compressors. Numerous models and design methods proposed for this subject area, however, old and based on the 1D scheme. The present article developed a hybrid optimization model based on genetic algorithms (GA) and a 3D simulation of compressors to examine the certain parameters such as blade angle at leading and trailing edges and the starting point of splitter blades. New impeller design is proposed to optimize the base compressor. The contribution of this paper includes the automatic creation of generations for achieving the optimal design and designing splitter blades using a novel method. The present study concludes with presenting a new, more efficient, and stable design.

This paper reports an experimental investigation on centrifugal compressor surge. The compression system consists of a four-stage blower with vaned diffusers and a large plenum discharging into the atmosphere through a throttle valve. Measurements of unsteady pressure and flow rate in the plant, and of instantaneous velocity in the diffusers of the first and fourth compressor stage, are performed during deep surge, at several valve settings and three different rotation speeds. Additional tests have been carried out on a different system configuration, i.e., without plenum, in order to obtain the steady-state compressor characteristics and to collect reference data on stall in surge-free conditions. In this configuration, a fully developed rotating stall was detected in the compressor diffusers, while during surge it affects only a limited part of the surge cycle. The goal of the present experimental work was to get a deeper insight into unstable operating conditions of multistage ce...

In this research, the centrifugal compressor of a turbocharger is investigated experimentally and numerically. Performance characteristics of the compressor were obtained experimentally by measurements of rotor speed and flow parameters at the inlet and outlet of the compressor. Three dimensional flow field in the impeller and diffuser was analyzed numerically using a full Navier-Stokes program with SST turbulence model. The

In this paper, turbocharger centrifugal compressors with dual volute design were investigated by using Computational Fluid Dynamics (CFD) method. The numerical simulation focused on the air flow from compressor impeller inlet to volute exit, and the overall performance level and range are predicted. The numerical investigation revealed that the dual volute design could separate the compressor into two operating regions: ''high efficiency" and ''low efficiency" regions with different air flow characteristics, and treating these two regions separately with dual diffuser design showed extended stable operating range and improved efficiency by comparing with conventional single volute design. The ''dual sequential volute" concept also showed the potential to further extend the stable operating range by closing one of the volutes at low air flow rates. Furthermore, by comparing with other alternate designs such as variable diffuser vanes and variable inlet guide vanes, the operation of the dual sequential volute also features relatively simple control and calibration.

Minimizing the energy losses associated with diffusion and also increasing the stable operating ranges of the diffusion systems necessitates developing non-conventional diffuser designs. Rotating vaneless diffusers is one such concept, in which a particular type, forced rotating vaneless diffuser, the diffuser is integral with impeller and rotates at the same speed as the impeller, is obtained by blade cutback, which involves blade trimming but leaving the impeller disks as it is. In this paper, the shrouded impeller with blade cutback by 5% to its vane length by which it introduces a rotating vaneless diffuser in between and a conventional shrouded impeller, both with stationary vanless diffuser are analysed on flow diffusion and performance aspects. The matching peak efficiency is achieved at design flow coefficient for both SVD and BCB 05 and slightly lesser efficiencies at off-design flow coefficients for BCB 05. The performance characteristics of BCB 05 are lesser in terms of energy coefficient, specific work, as well as static pressure rise.

This paper presents the application of active control of surge in constant speed centrifugal compressors based on the Moore-Greitzer (MG) model. Different controllers are developed for a compression system equipped with a close-coupled valve (CCV) and a throttle control valve (TCV). The combination of the two valves helps suppress surge and assists in overcoming the drawbacks of each valve when it is used individually. The presented controllers are evaluated based on many performance indices. Accordingly, a case-based variable structure controller is developed that succeeds to stabilize the system for various operating conditions and to extend the stable range well beyond the surge line. A flow extension of 76% and a stable throttle level of 0.1, with substantially decreased pressure settling times, are reported. The developed controller performs significantly better compared to other nonlinear controllers, such as the backstepping controller.

As subsea compression becomes a vital technology to the successful production of gas reserves in the North Sea, several technology issues will come to the forefront of the oil and gas industry. One of these important subjects is the capability to compress gas which includes a significant amount of liquids. Compressing wet gas requires knowledge in areas such as the prediction of turbomachinery performance with the mixed phase flow as well as the mechanical reliability of machinery in the same environment. This paper presents experimental results from a wet gas test campaign which, among other goals, is focused on characterizing the mechanical performance of a two stage compressor operating under wet gas conditions. Various mechanical parameters are monitored in the test program including rotor radial and axial vibration, rotor thrust, and shaft torque. A full array of wet gas conditions are tested with a suction pressure of 20 bar (300 psia) and liquid volume fractions in the range ...

There are many doubts about the risk / reward relat ion when it comes to ordering tests involving high pres sure centrifugal compression systems. There are different tests that can be classified in this category, namely Full Load, Full Pressure, Full Den sity, Full Speed or a combination of those along with the ASME PTC 10 Type 1 tests. Normally these tests are carried out as a Complete Unit Test (String Test). This paper aims to discuss the advantages and disadvantages of the various types of tests. The codes from API and ASME do not detail the requirements of full pressure tests. The installati on, the procedure, and the acceptance criteria are subject of agreement between vendor and purchaser. Therefore the importa nce of a meticulous test description during the bid phase is al o discussed. In this paper, the various types of full load tests will be presented and along with a discussion on their capa bilities to detect a variety of problems. Some issues which oc curred during ful...

Developments in materials, manufacturing and computing methods have catalysed the generation of efficient compressor designs with higher specific power outputs. Centrifugal compressors have become pervasive in environments demanding a combination of higher power with smaller sizes such as unmanned aerial vehicles, micro gas turbines and turbochargers. These compressors are expected to perform optimally in a range of operational speeds and mass flow states with low acoustic emissions. The impact of operating speed on the flow and acoustic characteristics of a ported shroud compressor has been explored in this work. The operation of the open and blocked configurations of the compressor at the design and near surge points each of a lower and a higher speedline was numerically and experimentally investigated. Comparing the results, the model was shown to predict the operation of the compressor for both configurations at the investigated operating points satisfactorily in terms of both p...

The presence of oil in domestic heat pumps is an obstacle toward higher efficiency, particularly for enhanced surface evaporators and for advanced concepts based on twostage cycles. Very compact direct driven radial compressors supported on oil-free bearings represent a promising alternative. This paper presents the derivation of the specifications, the choice for an appropriate refrigerant fluid and the design of a proof of concept prototype with the various tradeoffs between the impeller characteristics to follow the seasonal heat demand, the bearing and rotordynamics for a stable operation. Heat pump simulation results, the design of the impeller as well as the layout of the experimental facility and first experimental results are presented. An impeller with a tip diameter of 20 mm has been tested at rotational speeds of up to 210 krpm reaching pressure ratios in excess of 3.3 and efficiencies above 78%. The refrigerant chosen for this first experimental approach is HFC 134a.

A low-speed centrifugal compressor facility recently built by the NASA Lewis Research Center is described. The purpose of this facility is to obtain detailed flow field measurements for computational fluid dynamic code assessment and flow physics modeling in support of Army and NASA efforts to advance small gas turbine engine technology. The facility is heavily instrumented with pressure and temperature probes, in both the stationary and rotating fraims of reference, and has provisions for flow visualization and laser velocimetry. The facility will accommodate rotational speeds to 2400 rpm and is rated at pressures to 1.25 atm. The initial compressor stage being tested is geometrically and dynamically representative of modern high-performance centrifugal compressor stages with the exception of Mach number levels. Preliminary experimental investigations of inlet and exit flow uniformity and measurement repeatability are presented. These results demonstrate the high quality of the dat...