• 유체기계공업학회:학술대회논문집
• /
• 유체기계공업학회 2002년도 유체기계 연구개발 발표회 논문집
• /
• pp.258-263
• /
• 2002

A numerical analysis using 2-D unsteady compressible program is conducted to explain characteristics of rotating stall such as rotating speed and number of stall cells in an one-stage axial compressor. Unlike an axial compressor which has only a rotor, in one-stage axial compressor a rotating stall is generated by rotor/stator interaction and tack pressure rising without any artificial disturbance and modeling. As a back pressure is raised, the separation of suction side at blades is increased uniformly, but because of the discrepancy of blockage effect by stator, the disturbances are generated to form a stall cell. Once the stall cell is formed, regularly the stall cell are rotating through rotor blades. When the speed of rotor is design speed the rotating speed of stall cell is $83.3\%$ of rotor rotating speed. When the speed of rotor is $80\%$ of design speed, the speed of rotating stall is $88.2\%$ of rotor speed. The number of generated stall cell are also varied for rotor speed and back pressure.

• 대한기계학회논문집B
• /
• 제29권9호
• /
• pp.971-978
• /
• 2005

Effects of inlet distorted flow on performance, stall and surge are experimentally investigated for a high-speed centrifugal compressor. Tested results for the distorted inlet flow cases are compared with the result of the undistorted one. The performance of compressor is slightly deteriorated due to the inlet distortion. The inlet distortion does not affect the number of stall cell and the propagation velocity. It also does not change stall inception flow rate. However, as the distortion increases, stall starts at the higher flow rate for low speed and at the lower flow rate for high speed. For 50,000 rpm stall occurrs as the flow rate decreases, however disappears fur the smaller flow rate. This is due to the interaction of surge and stall. After the stall and surge interact, the number of stall cell decreases.

• 대한기계학회논문집B
• /
• 제22권9호
• /
• pp.1247-1254
• /
• 1998

The vaneless diffusers are widely used in industrial centrifugal compressors which are required to operate within a wide flow range. When very high pressure gases are handled by centrifugal compressor. rotating stall is a serious problem because of the occurance of large aerodynamic exciting forces. Rotating stall mostly often occurs in the impellers but it can occur in vaneless diffusers as well. In this experimental study, the rotating stall in vaneless diffuser with radial type centrifugal impeller was measured by changing the flow rate with I-type, X-type hotwire. As the result, it was cleared which type of rotating stall of the impeller stall would occur and how many stall cells would appear relating with the flow rate. As the flow rate reduced, the propagation speed of rotating stall was reduced. But the stall cell number unchanged with respect to the flow rate.

• 대한기계학회논문집B
• /
• 제22권2호
• /
• pp.153-161
• /
• 1998

This study describes the results of the analysis of measured rotating stall signal in a centrifugal compressor with vaneless diffuser. Unsteady flow and rotating stall in vaneless diffuser were investigated by measuring of unsteady velocity fluctuation using hot-wire anemometer. Experiments were carried out in several impeller rotating speeds, at different radius ratios. Single hot -wire was used to study the characteristics of rotating stall. As a result, the abrupt rotating stall was detected at all measured impeller rotating speeds and the several flow coefficients which are less than 0.16. The number of the stall cell was one at all measured rotational speeds, and the rotating direction was the same as that of the impeller. As the flow rate decreased, the profile of the phase averaged radial velocity component with time changed from a sawtooth to a sine wave.

• 유체기계공업학회:학술대회논문집
• /
• 유체기계공업학회 2003년도 유체기계 연구개발 발표회 논문집
• /
• pp.476-481
• /
• 2003

In this paper, the effect of circumferential inlet distortion on performance and stall has been experimentally investigated in a high-speed centrifugal compressor, comparing distorted cases with undistorted one. The performance of compressor was slightly deteriorated by defect of inlet static pressure which is caused by the circumferential inlet distortion. As stall was fully developed the inlet distortion did not affect the number of stall cell and the propagation velocity. It also did not affect stall inception at 40,000 and 50,000 rpm. However stall occurred at the lower flow rate for distorted flow at 60,000 rpm. For 50,000 rpm a unexpected phenomenon occurred : stall occurred first and then it disappeared.

• 유체기계공업학회:학술대회논문집
• /
• 유체기계공업학회 1999년도 유체기계 연구개발 발표회 논문집
• /
• pp.179-186
• /
• 1999

Three-dimensional flow analysis is implemented to investigate the flow through transonic axial-flow compressor rotor(NASA R67), and to evaluate the performances of k-$\epsilon$ and Baldwin-Lomax turbulence models. A finite volume method is used for spatial discretization. And, the equations are solved implicitly in time with the use of approximate factorization. Upwind difference scheme is used for inviscid terms, but viscous terms are centrally differenced. The flux-difference-splitting of Roe is used to obtain fluxes at the cell faces. Numerical analysis is performed near peak efficiency and near stall. And, the results are compared with the experimental data for NASA R67 rotor. Blade-to-Blade Mach number distributions are compared to confirm the accuracy of the code. From the results, we conclude that k-$\epsilon$ model is better for the calculation of flow rate and efficiency than Baldwin-Lomax model. But, the predictions for Mach number and shock structure are almost same.

• 대한기계학회논문집B
• /
• 제25권10호
• /
• pp.1384-1391
• /
• 2001

Three-dimensional flow analysis is implemented to investigate the flow through transonic axial-flow compressor rotor(NASA R67) and to evaluate the performances of Abid's low-Reynolds-number k-$\omega$ and Baldwin-Lomax turbulence models. A finite volume method is used fur spatial discretization. The equations are solved implicitly in time by the use of approximate factorization. The upwind difference scheme is used for inviscid terms and viscous terms are approximated with central difference. The flux-difference-splitting method of Roe is used to obtain fluxes at the cell faces. Numerical analysis is performed near peak efficiency and near stall. The results are compared with the experimental data for NASA R67 rotor. Blade-to-Blade Mach number distributions are compared to confirm the accuracy of the code. From the results, it is concluded that Abid'k-$\omega$ model is better for the calculation of flow rate and efficiency than Baldwin-Lomax model. But, the predictions for Mach number and shock structure are almost the same.

• 한국축산시설환경학회지
• /
• 제1권1호
• /
• pp.9-19
• /
• 1995

This study was carried out to investigate the effect of sawdust bedding barn on manure handing, management labour and physiological aspect of dairy cows, and then to establish the criteria on the optimum utilization method of sawdust bedding barn. 46 tie stall barns and 49 sawdust bedding barns were surveyed to cmopare the milk productivity between two different barns, and also 5 tie stall barns, 15 sawdust bedding barns and 1 rice hull bedding barn were selected to study the utilization situation of sawdust barn in Kyung-Ki province area. The major results obtained were as follows; 1. The roof material of sawdust barn were consisted of 66% vinyl house, 23% PVC light and 11% slate and galvanum coated tin. Most of the floor structure was earth ground with the rate of the approximately 82%. 2. The average occupied area of sawdust bed per cow was 15.2 $m^2$, depth that 30 cm and the utilization period was 12 months. 3. Milk Yield was significantly higher at sawdust barn than at tie stall barn(P<0.01). Bacterial and somatic cell count in raw milk were less at the sawdust barn than in tie stall barn. However, there was not significance difference between two barns. 4. The labour hour needed to cow management in the sawdust barn was approximately 48% of that of tie stall barn. 5. The temperature and moisture content measured in sawdust bed were closely affected by seasonal ambient temperature. The skin and hair of cow were much cleaner at the PVC light roofed sawdust barn than any other roof materials. 6. The additives used for improving of fermentation did not show any effect on temperature and moisture content in sawdust bed. When the ambient temperature was $30.4^{\circ}C$, the surface temperature of measured 1 cm above the sawdust bed was $12.2^{\circ}C$ lower and the temperature of 100 cm above the sawdust bed was $2.4^{\circ}C lower under shading net facility than that of vinyl roofed one.7. The hoof length of miking cow was 7.95 cm in tie stall and 9.19 cm in sawdust barn with high significance (P<0.01). And disease occurence such as mastitis and foot-rot tended to decrease in the sawdust barn. 8. The number of total bacteria and coliform bacteria were less in the sawdust bed compared with earth ground resting area. And a parasite strongyloides papillosus was detected but without any infected cow. 9. The nitrate($NO_3N$) content in non-roofed earth ground resting area and earth ground under the sawdust bed was likely to pollute the ground water. 10. In economic point of view, rice hull bedding barn was the cheapest among different systems. And in the sawdust bedding barn PVC light + slate roofed barn was most desirable, and vinyl roofed one the least.

• Asian-Australasian Journal of Animal Sciences
• /
• 제32권5호
• /
• pp.748-756
• /
• 2019

Objective: The objective of this study was to examine the effect of using a tunnel ventilation system within the dairy barn environment upon the productivity of dairy cows during the winter season. Methods: The study was performed at the University Farm, Faculty of Agriculture, Utsunomiya University. Twenty-one Holstein dairy cows (5 heifers and 16 multiparous) were enclosed in a stall barn. Unventilated (UV) and tunnel-ventilated (TV) was operated by turns every other week, and a number of key parameters were measured in the barn, including tunnel ventilation output, temperature, relative humidity, gas concentrations (oxygen [$O_2$], carbon dioxide [$CO_2$], and ammonia [$NH_3$]). Also, skin and rectal temperature, respiratory rate, blood gas concentrations, and bacterial count were measured from nipple attachments on ten cows. The amount of fodder left uneaten, and general components and somatic cell count of the milk were measured. Results: As for our dairy barn environment, air temperature dropped significantly with the passage of time with TV. Humidity was significantly higher with TV at 0600 h compared to UV, while $CO_2$ and $NH_3$ concentrations with UV were significantly higher than with TV at 0000 h and 0600 h. Skin temperature was significantly lower with TV compared to UV at 0000 h and 0600 h. Respiratory rate was also significantly lower at 0600 h with TV than with UV. Bacterial count for the nipple attachments was significantly lower with TV than with UV at 0600 h. The amount of leftover fodder was significantly less with TV in comparison with UV. Conclusion: Our results suggest that a TV system in the winter barn results in environmental improvements, such as reductions in unfavorable gas concentrations and bacterial growth. Consequently, it is expected that barns utilizing a TV system will be beneficial for both animal health and production.

• Journal of Animal Science and Technology
• /
• 제48권3호
• /
• pp.479-486
• /
• 2006

본 연구는 사양과 관리 방법이 낙농농가의 우유품질과 생산성에 미치는 효과를 조사하기 위하여 수행하였다. 조사농가는 경기 (11), 강원 (22)과 충남 (17) 지역의 50농가를 선정하여 사육규모, 우사형태, 사양관리, 분뇨처리, 착유와 생산성에 관한 자료를 수집하여 분석하였고 조사농가로부터 우유저장 탱크에서 우유 샘플을 채취하여 우유 성분과 품질을 분석하였다. 착유우의 사육 규모가 큰 농가가 중간 규모나 적은 규모의 농가에 비하여 우사, 착유관리와 분뇨처리를 위한 시설을 잘 갖추고 있었다. 착유우에 대한 농후사료 급여량이 소규모의 낙농가 (47.51%)가 중간 규모의 낙농가 (32.59%)나 규모가 큰 낙농농가 (31.81%)에 비하여 많은 양을 급여하고 있었으며, 착유우의 사육 규모가 커질수록 낙농 농가에서의 농후사료 급여수준이 감소되는 동시에 수입조사료에 대한 의존도는 증가하였다. 우유 중의 세균수는 우사 및 착유실의 형태에 따라서 영향을 받았으며, 계류식 우사에서 착유우를 사육하는 농가의 우유 중 세균수 (Coliform과 E. coli)가 후리스톨이나 톱밥우사에서 사육하는 농가에서 보다 높았다. 바켓식 착유를 하는 농가의 우유 중 세균수가 파이프라인이나 텐덤 (tendem)과 헤링본 착유시설을 보유한 농가에서 보다 높았다. 착유우의 사육두수가 많은 농가일수록 관리와 착유를 위한 시설이 개선되는 경향이 있어 체세포 등급이 높은 것으로 나타났고 체세포 등급이 높은 착유우에서 우유 생산성도 높았다. 그리고 조사된 농가의 평균 우유 중 단백질 농도는 2.89 에서 2.98% 이었고, 우유 중 요소태 질소 함량은 21.81에서 23.31mg/dl 이었다. 이런 결과는 착유 두수가 많은 농가일수록 착유우의 관리를 위한 시설을 개선하고 있어, 유질이 개선되고 농가의 수입도 더불어 증가하고 있는 것으로 조사되었다.