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Article
Publication date: 1 February 1945

V.D. Naylor

IN a recent article by the author, reference was made to the stalling of airscrew blades and to some of its effects. It seems worth while to examine more closely the kinematics of…

Abstract

IN a recent article by the author, reference was made to the stalling of airscrew blades and to some of its effects. It seems worth while to examine more closely the kinematics of stalling. In some cases the thrust coefficient graph for a chosen value of p/D indicates a marked drop in kT at a certain value of J, this drop being attributed to stalling of the blade; point ? on ABC (Fig. 1) is such a point. It seems certain that the effect of stalling is complete at C when the kT graph is practically parallel to the J axis, but where the effects of stalling first come into play is not so clear. In other cases, especially for lower values of p/D, the kT graph has the shape DE, from which it is not clear whether or not any stalling at all has taken place.

Details

Aircraft Engineering and Aerospace Technology, vol. 17 no. 2
Type: Research Article
ISSN: 0002-2667

Article
Publication date: 1 April 2005

Suat Canbazoğlu and Bekir Sami Yilbaş

A stall model to predict the performance of a blade row operating under rotating stall conditions, is proposed.

Abstract

Purpose

A stall model to predict the performance of a blade row operating under rotating stall conditions, is proposed.

Design/methodology/approach

The experiments were carried out on an isolated rotor row of an axial flow compressor of a radius ratio of 0.66 hub/tip. Wall static pressure tappings were used for measurement of blade row pressure rise. The mass flow rate through the machine was determined from the pressure drop at the intake. Detailed flow measurements were made using a hot wire “V” probe and transducers. An online data acquisition system was used in which data sampling was phase‐locked with respect to stall cell trailing edge.

Findings

Measurements indicate that a pressure depression occurs in the stalled region. The assumption of uniform static pressure at the exit of a stalled blade row is not supported by the present work. The assumption of uniform static pressure at the exit of a stalled row together with the assumption that flow in unstalled regions operates at fixed point on the unstalled characteristic leads to the conclusion that total‐to‐static pressure rise during stalled operation is independent of blockage. This view is not supported by the experiments carried out on an isolated rotor.

Research limitations/implications

Additional experimental studies for axial compressors having different rotor and blade geometries and rotor speeds, are required.

Practical implications

The results can be used in the design and operation of axial compressor rotors.

Originality/value

A new stall model is presented in which the behavior during stalled operation with large blockage is different from that during, low blockage.

Details

Aircraft Engineering and Aerospace Technology, vol. 77 no. 2
Type: Research Article
ISSN: 0002-2667

Keywords

Article
Publication date: 7 August 2017

Peijian Zhou, Fujun Wang and Jiegang Mou

Rotating stall is an unsteady flow phenomenon that causes instabilities and low efficiency in pumps. The purpose of this paper is to investigate the rotating stall characteristics…

Abstract

Purpose

Rotating stall is an unsteady flow phenomenon that causes instabilities and low efficiency in pumps. The purpose of this paper is to investigate the rotating stall characteristics and unsteady behavior of stall cells in a centrifugal pump impeller at low flow rates.

Design/methodology/approach

A developed large eddy simulation with dynamic mixed nonlinear model is performed to evaluate the unsteady flow in a centrifugal pump impeller. The rotating stall flow field through the centrifugal pump impeller is analyzed under three typical flow rates. Frequency spectrum analysis are carried out on the series of pressure fluctuation to get the rotating stall characteristics. The size and intensity of stall cells are also analyzed using time-averaged vorticity and static pressure.

Findings

The rotating stall cell first occurs in the suction side of the blade and exhibits an obvious life cycle including decay mergence, shedding, growing and development with a low frequency. With the decrease of flow rate, the amplitude of pressure fluctuations in the impeller tends to be larger, the propagated speed of stall cells and rotating stall frequency tends to be smaller, but the number of cells remains unchanged. The size of stall cells increases as the flow rate decreases, but intensity changes is very little.

Originality/value

The rotating stall characteristics in a centrifugal pump impeller under low flow rates are presented first using a developed large eddy simulation approach.

Details

Engineering Computations, vol. 34 no. 6
Type: Research Article
ISSN: 0264-4401

Keywords

Article
Publication date: 19 November 2021

M. R. Nived, Bandi Sai Mukesh, Sai Saketha Chandra Athkuri and Vinayak Eswaran

This paper aims to conduct, a detailed investigation of various Reynolds averaged Navier–Stokes (RANS) models to study their performance in attached and separated flows. The…

Abstract

Purpose

This paper aims to conduct, a detailed investigation of various Reynolds averaged Navier–Stokes (RANS) models to study their performance in attached and separated flows. The turbulent flow over two airfoils, namely, National Advisory Committee for Aeronautics (NACA)-0012 and National Aeronautics and Space Administration (NASA) MS(1)-0317 with a static stall setup at a Reynolds number of 6 million, is chosen to investigate these models. The pre-stall and post-stall regions, which are in the range of angles of attack 0°–20°, are simulated.

Design/methodology/approach

RANS turbulence models with the Boussinesq approximation are the most commonly used cost-effective models for engineering flows. Four RANS models are considered to predict the static stall of two airfoils: Spalart–Allmaras (SA), Menter’s kω shear stress transport (SST), k – kL and SA-Bas Cakmakcioglu modified (BCM) transition model. All the simulations are performed on an in-house unstructured-grid compressible flow solver.

Findings

All the turbulence models considered predicted the lift and drag coefficients in good agreement with experimental data for both airfoils in the attached pre-stall region. For the NACA-0012 airfoil, all models except the SA-BCM over-predicted the stall angle by 2°, whereas SA-BCM failed to predict stall. For the NASA MS(1)-0317 airfoil, all models predicted the lift and drag coefficients accurately for attached flow. But the first three models showed even further delayed stall, whereas SA-BCM again did not predict stall.

Originality/value

The numerical results at high Re obtained from this work, especially that of the NASA MS(1)-0317, are new to the literature in the knowledge of the authors. This paper highlights the inability of RANS models to predict the stall phenomenon and suggests a need for improvement in modeling flow physics in near- and post-stall flows.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 32 no. 4
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 1 April 1992

Nicholas Heal and Frances Plimmer

Considers the problems of rating valuations for street and indoormarkets. Discusses the most suitable way to solve them using threedifferent types of market as examples. Queries…

Abstract

Considers the problems of rating valuations for street and indoor markets. Discusses the most suitable way to solve them using three different types of market as examples. Queries whether the rates bill should be charged to the landlord or the occupier of the individual stall. Provides guidelines for the rating valuation of markets throughout the country.

Details

Journal of Property Valuation and Investment, vol. 10 no. 4
Type: Research Article
ISSN: 0960-2712

Keywords

Article
Publication date: 1 November 1950

K.W. Clark

SO much of the aircraft designer's attention has lately been diverted toward major developments such as supersonics, that there is some possibility of old‐established hazards like…

Abstract

SO much of the aircraft designer's attention has lately been diverted toward major developments such as supersonics, that there is some possibility of old‐established hazards like inadvertent stalls being forgotten. The only difference in these nowadays is that stalling speeds are generally higher and aircraft can strike the ground harder. There is perhaps therefore good reason for considering stalling hazards once again. In doing so, my remarks are confined to civil aircraft, partly because the safety of Service aircraft must often give way to their operational needs and partly because their accident statistics are not readily available for discussion.

Details

Aircraft Engineering and Aerospace Technology, vol. 22 no. 11
Type: Research Article
ISSN: 0002-2667

Article
Publication date: 1 September 2021

Vishal Raul and Leifur Leifsson

The purpose of this work is to investigate the similarity requirements for the application of multifidelity modeling (MFM) for the prediction of airfoil dynamic stall using…

Abstract

Purpose

The purpose of this work is to investigate the similarity requirements for the application of multifidelity modeling (MFM) for the prediction of airfoil dynamic stall using computational fluid dynamics (CFD) simulations.

Design/methodology/approach

Dynamic stall is modeled using the unsteady Reynolds-averaged Navier–Stokes equations and Menter's shear stress transport turbulence model. Multifidelity models are created by varying the spatial and temporal discretizations. The effectiveness of the MFM method depends on the similarity between the high- (HF) and low-fidelity (LF) models. Their similarity is tested by computing the prediction error with respect to the HF model evaluations. The proposed approach is demonstrated on three airfoil shapes under deep dynamic stall at a Mach number 0.1 and Reynolds number 135,000.

Findings

The results show that varying the trust-region (TR) radius (λ) significantly affects the prediction accuracy of the MFM. The HF and LF simulation models hold similarity within small (λ ≤ 0.12) to medium (0.12 ≤ λ ≤ 0.23) TR radii producing a prediction error less than 5%, whereas for large TR radii (0.23 ≤ λ ≤ 0.41), the similarity is strongly affected by the time discretization and minimally by the spatial discretization.

Originality/value

The findings of this work present new knowledge for the construction of accurate MFMs for dynamic stall performance prediction using LF model spatial- and temporal discretization setup and the TR radius size. The approach used in this work is general and can be used for other unsteady applications involving CFD-based MFM and optimization.

Details

Engineering Computations, vol. 39 no. 3
Type: Research Article
ISSN: 0264-4401

Keywords

Article
Publication date: 1 September 1955

T.R. Nonweiler

WRITING an introduction to an article by Mr S. B. Gates on Trailing‐Edge Flaps, which appeared in these columns in 1937, the Editor felt constrained to admit his bewilderment over…

Abstract

WRITING an introduction to an article by Mr S. B. Gates on Trailing‐Edge Flaps, which appeared in these columns in 1937, the Editor felt constrained to admit his bewilderment over the number and variety of types of high‐lift aid which then existed. Without intending any disrespect, I imagine that the progress of years must have added to his embarrassment. It has certainly added to the number of devices in use and under test.

Details

Aircraft Engineering and Aerospace Technology, vol. 27 no. 9
Type: Research Article
ISSN: 0002-2667

Article
Publication date: 6 July 2010

Hamed Sadeghi, Mahmoud Mani and S.M. Hossein Karimian

The primary purpose of this paper is to investigate the characteristics of the unsteady flow field in the wake of Eppler‐361 airfoil undergoing harmonic pitch oscillation in both…

1133

Abstract

Purpose

The primary purpose of this paper is to investigate the characteristics of the unsteady flow field in the wake of Eppler‐361 airfoil undergoing harmonic pitch oscillation in both pre‐stall and post‐stall regimes.

Design/methodology/approach

Experimental measurements were carried out to study the characteristics of the unsteady flow field within the wake of an airfoil. All of the experiments were conducted in a low‐speed wind tunnel, and the velocity field was measured by a hot‐wire anemometry. The airfoil was given a harmonic pitching motion about its half chord axis at two reduced frequencies of 0.091 and 0.273. All experimental data were taken at the oscillation amplitude of 8°. During the experiments, the mean angle of attack was altered from 2.5 to 10° that this made it possible to study the wake in both pre‐stall and post‐stall regimes.

Findings

From the results, it can be concluded that different velocity profiles are formed in the wake at different phase angles. In addition, the hysteresis of the velocity field in the wake is captured between increasing and decreasing incidences. It is also found that the velocity field in the wake is strongly affected by the operating conditions of the airfoil, e.g. mean angle of attack, reduced frequency and instantaneous angle of attack. Huge variations in the profiles of the wake are observed at high instantaneous angles of attack when the mean angle of attack is 10°, i.e. when the airfoil experiences significant oscillations beyond the static stall. It is concluded that this is due to dynamic stall phenomenon.

Practical implications

Findings of the present study give valuable information, which can be used to characterize wakes of micro air vehicles, helicopter's rotor blades, and wind turbine blades. In addition to this, present findings can be used to predict dynamic stall of the above applications.

Originality/value

The paper is the first to investigate the unsteady wake of Eppler‐361 airfoil and to predict the dynamic stall phenomenon of this airfoil.

Details

Aircraft Engineering and Aerospace Technology, vol. 82 no. 4
Type: Research Article
ISSN: 0002-2667

Keywords

Article
Publication date: 1 February 1937

H.B. Irving

THE change from the parallel wings of the now obsolescent biplane to the tapered wings of the monoplane, usually fitted with flaps, raised a great number of problems, both…

Abstract

THE change from the parallel wings of the now obsolescent biplane to the tapered wings of the monoplane, usually fitted with flaps, raised a great number of problems, both aerodynamic and structural. Work on these has been pursued vigorously during the past few years, but the designer is still some considerable distance from having all his questions answered. For instance, further information is required as to the relation between wing thickness and profile drag before it can be decided what is the maximum thickness which can be used, taking both aero‐dynamical and structural considerations into account. This question is complicated by the fact that, so far as the tip sections are concerned,. the indications are that the thickness ratio has important effects on the nature of the stall, violent or gentle. So, too, will such factors as centre line camber and position of maximum ordinate affect the nature of the stall in greater or Jess degree. Added to these factors there is, of course, the important one of the taper itself, including—as is now realised—the question as to the way in which the tapering is done, that is, whether by sweeping the trailing edge forward or the leading edge back, or, as is more usual, a combination of the two.

Details

Aircraft Engineering and Aerospace Technology, vol. 9 no. 2
Type: Research Article
ISSN: 0002-2667

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