Time filter

Source Type

Ji B.,Hubei Engineering University | Ji B.,Key Laboratory of Jet Theory and New Technology of Hubei Province | Peng X.X.,China Ship Scientific Research Center | Long X.P.,Hubei Engineering University | And 3 more authors.
Journal of Physics: Conference Series | Year: 2015

Results of cavitating turbulent flow simulation around a twisted hydrofoil were presented in the paper using the Partially-Averaged Navier-Stokes (PANS) method (Ji et al. 2013a), Large-Eddy Simulation (LES) (Ji et al. 2013b) and Reynolds-Averaged Navier-Stokes (RANS). The results are compared with available experimental data (Foeth 2008). The PANS and LES reasonably reproduce the cavitation shedding patterns around the twisted hydrofoil with primary and secondary shedding, while the RANS model fails to simulate the unsteady cavitation shedding phenomenon and yields an almost steady flow with a constant cavity shape and vapor volume. Besides, it is noted that the predicted shedding vapor cavity by PANS is more turbulent and the shedding vortex is stronger than that by LES, which is more consistent with experimental photos.

Xiao L.-Z.,Wuhan University | Xiao L.-Z.,Key Laboratory of Jet Theory and New Technology of Hubei Province | Long X.-P.,Wuhan University | Long X.-P.,Key Laboratory of Jet Theory and New Technology of Hubei Province
Zhejiang Daxue Xuebao (Gongxue Ban)/Journal of Zhejiang University (Engineering Science) | Year: 2015

The numerical method was conducted to analyze the development of the cavitation in annular jet pump (AJP), and the impacts of different inclined angle on the cavitation performance of AJP were comparatively analyzed. The following results were obtained. 1) Combined with mixture model and Schnerr-Sauer model, realizable k-ε model can reasonably simulate the cavitation phenomenon in AJP. 2) With the decreasing outlet pressure of the AJP, the cavitation area at the inner wall of the throat inlet will stretch alone the throat and the induced low pressure will extend to the axis. When the low pressure attaches to the axis, the cavitation in the throat boosts and the pump turns out to be under operating limits. 3) When cavitation number is larger than limited cavitation number, the efficiency of AJP varies little regardless of the developing cavitation. When cavitation number drops to the limited cavitation number, the performance of AJP suffers a great decrease, while the cavitation number will stay constant and the corresponding value is the limited cavitation number. 4) The smaller the inclined angle is, the smaller the corresponding limited cavitation number is and the better cavitation performance of AJP is. The cavitation cloud is easier to be induced at the center of the recirculation and the shearing layer with a smaller inclined angle. ©, 2014, Zhejiang University. All right reserved.

Xiao L.,Hubei Engineering University | Xiao L.,Key Laboratory of Jet Theory and New Technology of Hubei Province | Long X.,Hubei Engineering University | Long X.,Key Laboratory of Jet Theory and New Technology of Hubei Province
International Journal of Multiphase Flow | Year: 2015

Based on the experimental and numerical methods, the pump performance and inner flow details of annular jet pumps under three area ratios (cross sectional area ratio of throat and nozzle) were studied in the present paper. The cavity clouds forming at the shearing layer, recirculation center and throat inlet were captured via high speed video. The realizable k-ε turbulence model combined with mixture cavitation model was well validated by experimental results on the pump performance (pressure ratio and pump efficiency) and the static wall pressure distribution. When the annular jet pump works under the critical working condition, the pressure ratio and the pump efficiency experience a sudden drop. Simultaneously, the flow rate ratio and cavitation number keep constant regardless of the decreasing outlet pressure, since the main flow is filled with cavity clouds. Moreover, the inception and development of cavity cloud induced at the throat inlet were particularly studied in this paper. The cavitation in the throat experiences three stages (incipient, stable and unstable stage) before extending into the diffuser, in which the unstable stage signals the approaching ofthe critical working condition. The cavity cloud there fluctuates slowly and faintly, while it may suddenly expand over the whole throat and vanish immediately. When the cavity cloud extends into the diffuser with the closure place x/Dt<2.8 (Dt is the diameter of throat length), there is a low frequency cavity cloud surge. However, the surge disappears as the cavity cloud increases to the intermediate part of the diffuser. Additionally, based on imaging analysis method, the frequency characteristic of the cavity shedding in the diffuser was also studied. The shedding of cavity cloud in the diffuser experiences multiple periodicities when Lcav=3.25Dt (cavity length in diffuser), while there are two fundamental frequencies (58Hz and 6Hz) for Lcav=1.1Dt with the higher one corresponding to the shedding frequency. In the case of Lcav=3.25Dt, the detached cavity cloud in the diffuser is pushed downstream only by the re-entrant jet. However, the main flow plays an important role on accelerating the detached part downstream in the case of Lcav=1.1Dt. © 2015 Elsevier Ltd.

Xiao L.,Hubei Engineering University | Xiao L.,Key Laboratory of jet theory and new technology of Hubei Province | Long X.,Hubei Engineering University | Long X.,Key Laboratory of jet theory and new technology of Hubei Province | And 5 more authors.
Journal of Mechanical Science and Technology | Year: 2013

The flow within the annular jet pump (AJP), in some degree, resembles the annular wall jet developing in a pipe with great axial pressure gradient. In some working conditions, there exists the backflow near the centerline. However this differs from the case in a center jet pump (CJP) that the recirculation emerges near the inner wall of the throat. The recirculation in AJP affects a lot to its performance, especially when AJP is utilized to convey something alive, such as fish. This paper aims to numerically study the impact of two parameters, the flow ratio M and the area ratio A, on the location, size and formation of the recirculation in AJP. After being validated by the experimental results, the RNG k-e{open} turbulent model was adopted. It is found that: (1) As M increases, the width and height of the recirculation in AJP decreases, and the separation point of the recirculation shifts gradually far away from the nozzle exit while the reattachment point slightly moves; (2) As A becomes larger, the width and height of the recirculation enlarged, with M keeping constant; (3) For AJP with constant A, the recirculation emerges when M declines to a critical value, and the value varies linearly with A; (4) The Craya-Curtet number C t and the momentum ratio J, which take A and M into whole consideration, are also feasible in describing the disappearance of the recirculation. However the critical value of C t and J are different from that discovered in CJP. The critical C t increases with decreasing A and the critical momentum ratio J c experiences a linear relationship with A. © 2013 The Korean Society of Mechanical Engineers and Springer-Verlag Berlin Heidelberg.

Xiao L.Z.,Hubei Engineering University | Xiao L.Z.,Key Laboratory of Jet Theory and New Technology of Hubei Province | Long X.P.,Hubei Engineering University | Long X.P.,Key Laboratory of Jet Theory and New Technology of Hubei Province | And 4 more authors.
IOP Conference Series: Earth and Environmental Science | Year: 2014

Numerical simulations of unsteady cavitating turbulent flow around a Clark-Y hydrofoil were performed using the Large Eddy Simulation method under different attack angles. The shedding of the cavity cloud was captured and the numerical results of the total vapour volume accords well with the experimental results. In this paper the concept of entrainment ability (generally adopted in water jet) was firstly introduced to describe the process of the cavity shedding. Based on the integral time averaged Navier-Stokes equations, the integration of p+ρ1v2 was adopted to describe the entrainment ability. A horizontal line from upstream to the leading edge was defined to monitor the flow rate and entrainment ability being transferred to the suction side. It is found that the entrainment ability directly determines the level of the re-entrant jet, which sees a sudden rise at the breakdown of the cavity cloud with the re-entrant jet reaching to the leading edge. Moreover, compared with no-cavitating flow, the entrainment ability was greatly hindered by the intensive cavity cloud over the foil. The pressure fluctuation at the trailing edge can be transferred upstream through the pressure side and influences the entrainment ability and flow rate across Line B(QB, Line B is defined as a horizontal line from upstream to the leading edge). In addition, as the attack angle increases, the time averaged QB greatly increases, while the time averaged entrainment ability experiences a marginal rise. Thus, the variation of attack angle only impacts the entrainment ability from Line A (mA), since mA varies linearly with QB. © Published under licence by IOP Publishing Ltd.

Loading Key Laboratory of jet theory and new technology of Hubei Province collaborators
Loading Key Laboratory of jet theory and new technology of Hubei Province collaborators