Effects Of Tip Clearance Size Research Articles

The effect of tip clearance size on pre-stall flow features of a transonic axial compressor by using throttle model

This paper aims at the numerical analysis of the influence of tip clearance size on the pre-stall flow features of a transonic high-speed compressor by applying the throttle model at the exit of the compressor computational domain. Steady and unsteady calculations have been performed for design, double, and triple tip clearance sizes. The transition of the stall inception type when increasing the tip clearance size and the underlying flow physics has been analyzed in detail. The results show that the stall inception type transforms from spike to modal as the size of the tip clearance changes from design to triple tip clearance. The influence of the tip clearance size on the forward spillage of the tip leakage vortex near the stall limit, which is one of the two criteria for spike stall inception, is crucial for which type of stall inception would appear. For the design clearance case, a remarkable forward spillage of the tip leakage vortex occurs near the stall limit, leading to a typical strong spike stall inception. In the condition of double clearance, the intensity of tip leakage vortex spillage was weakened because the increase in the clearance size allows more low momentum tip leakage flow to go through the clearance instead of spilling from the leading edge. Thus, a weaker spike-type inception containing the content of modal disturbances was induced. Under the triple clearance condition, the high entropy gradient interface is located inside the blade passages all the time; thus, a typical modal-type stall inception appears.

Effect of Tip Clearance Size on the Cavitation Flow and Noise Characteristics of the NACA0009 Hydrofoil

The noise characteristics of NACA0009 hydrofoil with tip clearance are discussed. Select SST k- ω Turbulence model and Schnerr Sauer cavitation model simulate tip leakage cavitation flow. The results show that the simulation results are in good agreement with the original records, and the tip clearance reduces the energy characteristics of the hydrofoil. With the expansion of tip clearance model, TLV and cavitation compressive strength gradually decrease. In addition, the study of far-field noise shows that the nonspecific curve of the total noise coefficient of far-field noise shows a disc shaped symmetric structure. Compared with the original hydrofoil, when the tip clearance is 20 mm, the far-field dipole noise value at 170 ° angle is reduced by 17.68%. Tip clearance reduces offline and far-field noise. Far field noise decreases with the increase of tip clearance model.

Effect of Tip Clearance Size on Tubular Turbine Leakage Characteristics

To study the effect of tip clearance on unsteady flow in a tubular turbine, a full-channel numerical calculation was carried out based on the SST k–ω turbulence model using a power-plant prototype as the research object. Tip leakage flow characteristics of three clearance δ schemes were compared. The results show that the clearance value is directly proportional to the axial velocity, momentum, and flow sum of the leakage flow but inversely proportional to turbulent kinetic energy. At approximately 35–50% of the flow direction, velocity and turbulent kinetic energy of the leakage flow show the trough and peak variation law, respectively. The leakage vortex includes a primary tip leakage vortex (PTLV) and a secondary tip leakage vortex (STLV). Increasing clearance increases the vortex strength of both parts, as the STLV vortex core overlaps Core A of PTLV, and Core B of PTLV becomes the main part of the tip leakage vortex. A “right angle effect” causes flow separation on the pressure side of the tip, and a local low-pressure area subsequently generates a separation vortex. Increasing the gap strengthens the separation vortex, intensifying the flow instability. Tip clearance should therefore be maximally reduced in tubular turbines, barring other considerations.

Effects of tip clearance size on vortical structures and turbulence statistics in tip-leakage flows: A direct numerical simulation study

Direct numerical simulations of the tip-leakage flow, generated by a gap between a straight National Advisory Committee for Aeronautics 0012 hydrofoil and the end wall of a channel, have been performed to investigate the effects of tip clearance size on vortical structures and turbulence statistics. The tip-leakage vortex, tip separation vortex, and induced vortex are the predominant vortical structures in tip-leakage flow for a relatively large gap (3.33%Ca), while the reverse flow vortex dominates the tip clearance region for smaller gaps (1.67%Ca), where Ca is the truncated chord length of the hydrofoil. Detailed analysis of turbulence statistics reveals that the tip-leakage vortex is caused by the rollup of the tip-leakage jet, while the spanwise inflow interacting with the sidewall of the hydrofoil leads to the formation of a reverse flow vortex. The turbulent kinetic energy contours show an arc-shaped distribution on the suction side of the hydrofoil, but their locations are significantly affected by the tip clearance size. In addition, the investigation of tip-leakage loss indicates that increasing the size of the tip clearance can reduce the tip-leakage loss across the hydrofoil. This can be attributed to the dominant vortical structures in the tip-leakage flow.

Experimental investigation of cavitation instabilities in inducer with different tip clearances

To investigate the effect of tip clearance size on cavitation characteristics in a turbopump inducer, a series of experiments have been conducted in a newly developed visualization test facility using room temperature water as working fluid. The pressure fluctuations near the tip region were collected, and the cavity structures under various conditions were documented by a high-speed camera. It is found that large tip clearance distinctly reduces both the non-cavitation and cavitation performance. Three cavitation instabilities, super-synchronous rotating cavitation, synchronous rotating cavitation and cavitation surge have been carefully identified through combination of cross-correlation analysis of pressure signals and visualization results. Large tip clearance displays a remarkable stabilization effect on pressure fluctuation, cavitation surge totally disappears, and the range of occurrence of synchronous rotating cavitation becomes smaller for the large tip clearance, whereas super-synchronous rotating cavitation only occurs in the large tip clearance. The cavitation areas are smaller at large tip clearance, while the flow channels are more seriously choked when cavitation occurs heavily in comparison with those at small tip clearance, which may be responsible for the worse cavitation performance.

Effects of Tip Clearance Size on Energy Performance and Pressure Fluctuation of a Tidal Propeller Turbine

Unavoidable tip clearance between blade tip and casing shroud plays an important role in the performance and characteristics of a tidal propeller turbine. In this work, the tip-leakage vortex (TLV) induced in the end-wall region was numerically illustrated by using the shear-stress transport (SST) k–ω turbulence model at various flow conditions and different tip-clearance sizes (TCSs). The swirling strength criterion was employed to visualize the tip-leakage vortex trajectory and investigate vortex evolution according to clearance size change. Although TLV occurs in both design and off-design conditions, vortex intensity develops strongly under excess flow rate with increased tip gap. The extreme influence of TCS on the turbine’s generated power and efficiency was predicted in steady simulations for four TCS cases, namely, δ = 0%, 0.25%, 0.5%, and 0.75%. With the extension of the tip gap, turbine performance was drastically reduced because of vigorous turbulent leakage flow combined with considerable volumetric loss. The effect of TCS on pressure fluctuation intensity were also explored on the basis of the transient simulation statistic. Maximal pressure variation amplitude and dominant frequency were presented in spectrum analysis utilizing fast Fourier transform.

Effect of tip clearance size on the performance of a low-reaction transonic axial compressor rotor

This study aimed to enhance the understanding of flow phenomena in low-reaction aspirated compressors. Three-dimensional, multi-passage steady and unsteady numerical simulations are performed to investigate the performance sensitivity to tip clearance variation on the first-stage rotor of a multistage low-reaction aspirated compressor. Three kinds of tip clearance sizes including 1.0τ, 2.0τ and 3.0τ are modeled, in which 1.0τ corresponds to the designed tip clearance size of 0.2 mm. The steady numerical simulations show that the overall performance of the rotor moves toward lower mass flow rate when the tip clearance size is increased. Moreover, energy losses, efficiency reduction and stall margin decrease are also observed with increasing tip clearance size. This can be mostly attributed to the damaging impact of intense tip clearance flow. For unsteady simulation, the result shows periodical oscillation of the tip leakage vortex and a “two-passage periodic structure” in the tip region at the near-stall point. The occurrence of the periodical oscillation is due to the severe interaction between the tip clearance flow and the shock wave. However, the rotor operating state is still stable at this working point because a dynamic balance is established between the tip clearance flow and incoming flow.

설계조건에서 선형 익렬의 익단 간극 크기가 익단 간극 누설유동에 미치는 영향에 관한 수치해석

A steady-state Reynolds averaged Navier-Stokes simulations was conducted to investigate the effect of tip clearance size on the distribution of tip leakage flow inside a linear cascade. Two different tip clearance size, t=2 mm and 4 mm, were considered under design condition(i.e. inlet flow angle β = 29.3°). As the tip clearance increased, the gradient of the static pressure trough at the endwall became larger and the tip leakage flow rolled-up more strongly in a helical form. In addition, high total pressure loss region corresponding to the distribution of tip leakage vortex was somewhat enlarged in the downstream positions of the blade trailing edge. The flow rate through the tip clearance increased in proportion to tip clearance size, and as a result, the swirling flow became stronger, so that the center of tip leakage vortex moved more from the blade tip to the hub. Additionally, the region with high turbulent intensity where the leakage flow exited the tip clearance in the form of jet, was extended to the inside of the flow path along the endwall. Finally, it was confirmed that there were several indicators to confirm the existence of tip leakage vortex. The defect of axial velocity in the tip region of blade flow path, the dimensionless helicity with a magnitude close to 1, the endwall pressure trough, the region with high total pressure loss, and strong roll-up of the particle trajectory were the typical examples. By taking these indicators as a comprehensive consideration, the existence of tip leakage vortex can be effectively found.

Effects of tip clearance size on the unsteady flow behaviors and performance in a counter-rotating axial flow compressor

This paper presents the studies performed to better understand the effects of increased tip clearance size on the unsteady flow behaviors and overall performance under the rotor–rotor interaction environment in a counter-rotating axial flow compressor. The investigation method is based on the three-dimensional unsteady Reynolds-averaged Navier–Stokes simulations. The results show that the intensified tip leakage flow in front rotor (R1) caused by the increased tip clearance size will lead to the growth of incoming incidence angle near the tip of the rear rotor (R2). The increasing of double leakage flow range plays a significant role in the sensitivity of the efficiency to tip clearance size and its extent is enlarged gradually with the increase of tip clearance size. As the tip clearance size is increased to 1.5τ (τ represents the designed tip clearance size) from 0.5τ, the results of the fast Fourier transform for the static pressure near blade tip show that two other new fluctuating frequency components appear due to the happening of tip leakage flow self-unsteadiness in R1 and R2, respectively. Additionally, the fluctuating strength near the tip in R2 is significantly increased. However, both the overall fluctuation in R1 caused by the potential effect from downstream and the oscillation in the hub corner on the pressure side of R2 are decreased obviously. The relative inflow angle tends to increase when the incoming wakes and tip leakage flow from R1 encounter the blade leading edge of R2, which leads to the result that the trajectory of tip leakage flow is shifted more upstream.

Numerical investigation of tip clearance size effect on the performance and tip leakage flow in a dual-stage counter-rotating axial compressor

Based on a validation of the numerical methods with an experiment, numerical simulations are carried out to study the effect of tip clearance size on the performance and tip leakage flow in a dual-stage counter-rotating axial compressor. The predicted results showed that the variation of the tip clearance size in rotor2 has a more significant impact on the overall performance and stall margin of the compressor. In addition, the impact of the tip clearance size effect is mainly on the rotor with the tip clearance size variation. The variation of the tip clearance size in rotor2 almost has no influence on the performance of rotor1, while the performance of rotor2 is increased about 1.37% at near-stall point when the tip clearance size of rotor1 is increased to 1.0 mm from 0.5 mm. At peak efficiency condition, the tip clearance size variation in rotor1 has remarkable influence on the tip leakage vortex intensity, onset point and trajectory in rotor1, but has little influence on those in rotor2. However, the tip clearance size variation in rotor2 has remarkable effect on those in both rotors. Different tip clearance size combination schemes can impact the stall-free characteristic in the counter-rotating axial compressor.

Role of tip injection in desensitizing the compressor to the tip clearance size

Numerical simulations are performed to investigate the role of tip injection in desensitizing a transonic compressor rotor to the detrimental effects of tip leakage flow. First, the effects of tip clearance size on the compressor stability and performance are investigated. Endwall injection of high-speed fluid upstream of the blade is then applied to the compressor with different tip clearance sizes. Results reveal that tip injection can effectively desensitize the compressor stability to the tip clearance size and improve the total pressure ratio, at the expense of some efficiency loss. It is further found that the larger the tip clearance size, the greater the stability enhancement and the smaller the efficiency penalty due to injection. The near-stall endwall flow structures for different tip clearance sizes, with and without injection, are also investigated in the current study. Results suggest that tip clearance size does not influence the compressor stalling mode, whereas endwall injection has the potential to change it (i.e., from “wall-stall” to “blade-stall” with the injection applied in the current study).

Effects of tip clearance size on the performance and tip leakage vortex in dual-rows counter-rotating compressor

Based on the preliminary validation of the numerical results with an experiment, the steady results of different tip clearance size effects on the performance and tip leakage vortex of counter-rotating compressor were discussed. The predicted results showed that the stable margin and isentropic efficiency of the counter-rotating compressor decreased with increasing of the tip clearance size. Furthermore, increasing the tip clearance size had a greater negative effect on the performance of the upstream rotor than the downstream rotor. Detailed flow field analyses further demonstrated that the unstable flow occurred in the two counter-rotating rotors with greater tip clearance size. The rotor downstream was the main unstable factor which caused the counter-rotating compressor to breakdown when a smaller tip clearance size was used.

Effects of Tip Clearance Size on Flowfield in a Low-Speed Axial Compressor Rotor

The simulations of a low-speed axial compressor rotor with two tip clearance sizes, 0.5% chord and 1.5% chord, were performed in the study. Overall performance and detailed flow fields at near stall condition are analyzed. The results show that the rotor stall occurs at higher mass flow condition with large tip clearance. For the small tip clearance the tip leakage vortex and the corner vortex both contribute significantly to the rotor stall, and the interaction between the vortices promotes the stall generation. While for the large tip clearance the tip leakage vortex plays a primary role, and the vortices interaction is ignorable.

Numerical Simulation on Axial Flow Fan Performance with Changing Tip Clearance

Taking the relative tip clearance as the variable, we numerically simulated the effect of tip clearance size on the performance of a straight-blade axial flow fan using the 3-D viscous flow solver. The tip clearance is referenced in the relative value. By comparing the flow field corresponding to five different values of the tip clearance 0, 0.5%, 1.0%, 1.5% and 2.0% with other parameters kept constant, we concluded that the changing of the tip clearance has a great influence on the performance of the axial flow fan. Both the efficiency and the total pressure decrease with the increase of the tip clearance.

145 超高負荷円環翼列内の流れの数値解析 : 翼端間隙高さと翼形状による影響(流体工学III,一般講演)

145 超高負荷円環翼列内の流れの数値解析 : 翼端間隙高さと翼形状による影響(流体工学III,一般講演)

Effect of Tip Clearance on the Prediction of Nonsynchronous Vibrations in Axial Compressors

This work investigates the effect of tip clearance size and operating temperature on the predictions of the critical rotor speed at which nonsynchronous vibrations (NSV) can be encountered in a turbine engine axial flow compressor. It has been proposed that the tangential tip clearance flow, observed at high blade loading near stall, can act as an impinging resonant jet on the upcoming blades and could be the underlying physics behind NSV. A model, in the form of an equation to predict the critical blade tip speed at which NSV can occur, was proposed based on the Jet-Core Feedback Theory and was experimentally verified by Thomassin et al. (2008, “Experimental Demonstration to the Tip Clearance Flow Resonance Behind Compressor NSV,” Proceedings of GT2008: ASME Turbo Expo Power for Land, Sea and Air, Berlin, Germany, Jun. 9–13, Paper No. GT2008-50303). In the equation, a factor k that was called the “tip instability convection coefficient” was measured experimentally and found to be influenced by the tip clearance size and operating temperature. This factor has a significant impact on the accuracy of the NSV predictions obtained using the proposed model. This paper propose a numerical experiment to determine the effect of tip clearance size and temperature on k, in order to improve the critical NSV tip speed predictions using the proposed model. A review of the NSV model is presented along with the relevant background theory on the subject. Two different blade geometries are simulated to provide a generic approach to the study. The leakage flow velocity is calculated to estimate k and a correlation is proposed to model the behavior of the k parameter as a function of the tip clearance size. The latter was found to significantly improve the critical NSV speed predictions. The effect of operating temperature on k is also discussed. Finally, the variation of k with the aerodynamic loading is assessed and compared with available data in the literature to strengthen the generic nature of the results.

Numerical simulation on the effect of tip clearance size on unsteadiness in tip clearance flow

Unsteadiness of tip clearance flow with three different tip clearance sizes is numerically investigated in this paper. NASA Rotor 67 is chosen as the computational model. It is found that among all the simulated cases, the unsteadiness exists when the size of the tip clearance is equal to or larger than design tip clearance size. The relative total pressure coefficient contours indicate that region of influence by tip leakage flow augments with the increase of tip clearance size at a fixed mass flow rate. Root Mean Square contours of static pressure distribution in the rotor tip region are provided to illustrate that for design tip clearance (1.1% tip chord) the strongest fluctuating region is located on pressure side of blade near leading edge, while for the larger tip clearance (2.2% tip chord), it is in the region of the interaction between the shock wave and the tip leakage flow.

Measurements of the Tip Clearance Flow for a High-Reynolds-Number Axial-Flow Rotor

A high-Reynolds-number pump (HIREP) facility has been used to acquire flow measurements in the rotor blade tip clearance region, with blade chord Reynolds numbers of 3,900,000 and 5,500,000. The initial experiment involved rotor blades with varying tip clearances, while a second experiment involved a more detailed investigation of a rotor blade row with a single tip clearance. The flow visualization on the blade surface and within the flow field indicate the existence of a trailing-edge separation vortex, a vortex that migrates radially upward along the trailing edge and then turns in the circumferential direction near the casing, moving in the opposite direction of blade rotation. Flow visualization also helps in establishing the trajectory of the tip leakage vortex core and shows the unsteadiness of the vortex. Detailed measurements show the effects of tip clearance size and downstream distance on the structure of the rotor tip leakage vortex. The character of the velocity profile along the vortex core changes from a jetlike profile to a wakelike profile as the tip clearance becomes smaller. Also, for small clearances, the presence and proximity of the casing endwall affects the roll-up, shape, dissipation, and unsteadiness of the tip leakage vortex. Measurements also show how much circulation is retained by the blade tip and how much is shed into the vortex, a vortex associated with high losses.