On the Flow Behavior in Rotor-Stator System with Superposed Flow

The flow between a rotor and a stator at high Reynolds number and small Ekman number is divided into three domains, two boundary layers adjacent to the discs separated by a central core. In the present work, a simple theoretical approach provides analytical solutions for the radial distribution of the core swirl ratio valid for a rotor-stator system with a superposed radial inflow rate. At first, the flow in the rotor boundary layer is assumed to behave as expressed by Owen and Rogers (1989) in the case of a turbulent flow on a rotating single disc. On the stator side, a necessary compensation flow rate must take place according to the conservation of mass. It is found that this compensation flow rate cannot be estimated with a good accuracy using the hypotheses of a stationary disc in a rotating fluid by Owen and Rogers (1989). Thus, two innovative weighting functions are tested, leading to new analytical laws relating the core swirl ratioKto the coefficient of flow rateCqrintroduced by Poncet et al. (2005). The adequacy between the theoretical solutions and numerous results of the literature is clearly improved and the discussion allows a better understanding of the flow behavior.

Download Full-text

Some Improvements in a Gas Turbine Stator-Rotor Systems Core-Swirl Ratio Correlation

International Journal of Rotating Machinery ◽

10.1155/2012/853767 ◽

2012 ◽

Vol 2012 ◽

pp. 1-9

Author(s):

R. Da Soghe ◽

B. Facchini ◽

L. Innocenti ◽

M. Micio

Keyword(s):

Swirl Ratio ◽

Rotating Fluid ◽

One Dimensional ◽

Rotor Systems ◽

Solid Body Rotation ◽

The Core ◽

Turbine Stator ◽

Experimental Correlation ◽

Ratio Correlation ◽

Good Agreement

The present work concerns the turbulent flow inside a rotor-stator cavity with superimposed throughflow. The authors focused their analysis on a simple two-faced disk cavity, without shrouds, with interdisk-spacing sufficiently large so that the boundary layers developed on each disk are separated and the flow is turbulent. In such a system, the solid body rotation of the core predicted by Batchelor can develop. The evolution of the core-swirl ratio of the rotating fluid with an outward throughflow is studied by applying a classical experimental correlation, inserted in a one-dimensional (1D) in-house developed code. Results are compared to those predicted by CFD computations. Due to the discrepancies revealed, the authors provided a correction of the experimental correlation, based on CFD computation. Results thus obtained are finally in good agreement with CFD predictions.

Download Full-text

Passive scalars in turbulent channel flow at high Reynolds number

Journal of Fluid Mechanics ◽

10.1017/jfm.2015.711 ◽

2016 ◽

Vol 788 ◽

pp. 614-639 ◽

Cited By ~ 44

Author(s):

Sergio Pirozzoli ◽

Matteo Bernardini ◽

Paolo Orlandi

Keyword(s):

Reynolds Number ◽

Channel Flow ◽

High Reynolds Number ◽

Correction Term ◽

Scalar Dissipation ◽

Channel Height ◽

Passive Scalars ◽

The Core ◽

The Mean ◽

High Reynolds

We study passive scalars in turbulent plane channels at computationally high Reynolds number, thus allowing us to observe previously unnoticed effects. The mean scalar profiles are found to obey a generalized logarithmic law which includes a linear correction term in the whole lower half-channel, and they follow a universal parabolic defect profile in the core region. This is consistent with recent findings regarding the mean velocity profiles in channel flow. The scalar variances also exhibit a near universal parabolic distribution in the core flow and hints of a sizeable log layer, unlike the velocity variances. The energy spectra highlight the formation of large scalar-bearing eddies with size proportional to the channel height which are caused by a local production excess over dissipation, and which are clearly visible in the flow visualizations. Close correspondence of the momentum and scalar eddies is observed, with the main difference being that the latter tend to form sharper gradients, which translates into higher scalar dissipation. Another notable Reynolds number effect is the decreased correlation of the passive scalar field with the vertical velocity field, which is traced to the reduced effectiveness of ejection events.

Download Full-text

Separation and free-streamline flows in a rotating fluid at low Rossby number

Journal of Fluid Mechanics ◽

10.1017/s0022112087001472 ◽

1987 ◽

Vol 179 ◽

pp. 155-177 ◽

Cited By ~ 10

Author(s):

Michael A. Page

Keyword(s):

Potential Flow ◽

High Reynolds Number ◽

Numerical Data ◽

Critical Value ◽

Rossby Number ◽

Rotating Frame ◽

Rotating Fluid ◽

Ekman Number ◽

Classical Potential ◽

High Reynolds

The flow past a circular cylinder in a rotating frame is examined when the Rossby number Ro is O(E½), where E is the Ekman number. Previous studies of the configuration have shown that, provided the ratio Ro/E½ is less than a certain critical value, the flow around the cylinder is determined by the classical potential-flow solution. However, once Ro/E½ is greater than that critical value the E1/4 layer on the surface of the cylinder, which is rather like a boundary layer in a high-Reynolds-number non-rotating fluid, can separate from the cylinder and distort the potential flow. In this study the form of the flow once separation has occurred is examined using a method analogous to the Kirchhoff free-streamline theory in a non-rotating fluid. The results are compared with published experimental and numerical data on the flow for various values of Ro/E½.

Download Full-text

Circumferential Combustor Cavity Flow Fields With Decreasing Core Flow

Volume 4A: Combustion, Fuels, and Emissions ◽

10.1115/gt2020-14151 ◽

2020 ◽

Author(s):

Brian T. Bohan ◽

Marc D. Polanka ◽

Larry P. Goss

Keyword(s):

Mass Flow Rate ◽

Mass Flow ◽

Flow Rate ◽

Axial Length ◽

Flow Behavior ◽

Cavity Flow ◽

Core Flow ◽

Cold Flow ◽

The Core ◽

Core Flows

Abstract Prior research into Ultra Compact Combustors (UCC) showed an axial length savings compared to traditional gas-turbine combustors. This savings is achieved by swirling the reactants circumferentially in a recessed cavity around the outside diameter of the engine. A similar circumferential combustor is envisioned for a new engine configuration that positions the combustor outboard of a radial compressor and an inflow turbine. This configuration will offer an axial length savings for the entire engine, not just the combustor. The new engine configuration will not utilize a core flow path and thus requires all engine air from the compressor to pass through, or around, the combustor cavity. This report characterizes the cavity flow behavior as the core flow quantity was reduced from 80% of the total engine mass flow rate down to zero, representing the new engine configuration, while maintaining constant cavity mass flow rates. Velocity profiles were obtained with particle-shadow image velocimetry (PSV) in cold flow and with particle streak emission velocimetry (PSEV) in reacting flow experiments. The cold flow results showed that the core flow produced a suction and removed fluid from the circumferential cavity resulting in a lower cavity mass flow rate. This behavior resulted in lower circumferential velocities at higher core flow percentages and the fastest cavity velocity with zero core flow. Reacting flows produced a similar result with the fastest cavity velocities achieved at reduced, but non-zero core flows, and the slowest velocities at the highest and zero core flows. Overall, it was found that there was no negative impact on performance from the removal of the core flow that would prohibit development of the new engine.

Download Full-text

Influence of a Weak Superposed Centripetal Flow in a Rotor-Stator System for Several Pre-Swirl Ratio

ASME-JSME-KSME 2011 Joint Fluids Engineering Conference: Volume 1, Symposia – Parts A, B, C, and D ◽

10.1115/ajk2011-16016 ◽

2011 ◽

Author(s):

Fadi Abdel Nour ◽

Roger Debuchy ◽

Ge´rard Bois

Keyword(s):

Boundary Layers ◽

Flow Behavior ◽

Central Core ◽

Major Influence ◽

Swirl Ratio ◽

Mean Velocity ◽

Core Flow ◽

Dimensionless Coefficient ◽

Gap Ratio ◽

High Reynolds

The present study is devoted to the influence of a superposed centripetal flow q in a rotor-stator cavity with a peripheral opening. In the literature, previous works have already shown that a weak radial inflow has no major influence near the periphery of the cavity, whereas the flow behavior is strongly modified when approaching the axis [1–2]. The challenge of this work is to give a better understanding of this phenomenon. Attention is focused on a rotor-stator system characterized by a small gap ratio G and high Reynolds number Re, so that the flow is divided into two boundary layers separated by a core region, according to the classification by Daily and Nece [3]. Until now, numerous authors obtained analytical solutions for the central core flow behavior: following the analysis performed by Schlichting [4], and assuming that the evolution of the velocity in the Ekman boundary layer corresponds to a 1/7 power law, Poncet et al. [2] proposed an analytical law predicting the evolution of the core swirl ratio K versus a local dimensionless coefficient of flow rate Cqr. Debuchy et al. [5] improved this last solution by taking into account the radial exchange of fluid outside the boundary layers. This last approach was used by Abdel Nour et al. [6] in a rotor-stator cavity without any superposed flow (isolated cavity). They obtained an original analytical law, different from the classical similitary solution proposed by Batchelor [7] in the case of infinite disc, convenient for a cavity with peripheral opening and small pre-swirl ratio. In this paper, the authors present an original analytical law in order to model the central core flow behavior in a rotor-stator cavity subjected to a very weak inflow rate (q → 0). The validity of the solution is tested with the help of: • a new set of experimental data including the radial and tangential mean velocity measured by hot-wire anemometry, • experimental results from the literature.

Download Full-text