ZHANG Chenglong, ZHANG Hui, JIANG Daiwen. Amplification mechanism of the velocity response with the effect of electro-magnetic force in channel flow[J]. 2020, 38(3): 490-499.
ZHANG Chenglong, ZHANG Hui, JIANG Daiwen. Amplification mechanism of the velocity response with the effect of electro-magnetic force in channel flow[J]. 2020, 38(3): 490-499.DOI: 10.7638/kqdlxxb-2019.0165.
Amplification mechanism of the velocity response with the effect of electro-magnetic force in channel flow
The flow of the weak electrolyte solution can be controlled by electromagnetic forces generated by the suitably chosen magnetic and electric fields
which has significant effects for applications in the drag reduction
lift amplification
and oscillatory suppression. However
the control efficiency is very low due to the application of a large amplitude for the electromagnetic force. Therefore
the large response
induced by a small electromagnetic force
is the key to enhance the flow control effic
iency. In this paper
based on the laminar flow of a weakly conductive fluid in a channel
the flow responses are induced by the electromagnetic force
which is applied on the lower wall of the channel and is cosine distribution along the spanwise direction. The analytic solutions of the velocity responses in linear stage are deduced with linear stability theory
and the numerical solutions of these responses in nonlinear stage are calculated with direct numerical simulation (DNS). For the periodic characters of the channel flow in the streamwise and spanwise directions
the dealiased Fourier method is used in these two directions
while the Chebyshev-tau method is used in the wall-normal direction. Moreover
the usual no-slip and no-penetration conditions are used on the walls. The time advancement is performed with third-order accuracy by using a semi-implicit back-differentiation formula method. To eliminate residual divergence
the pressure term and the linear term are solved with a Chebyshev-tau influence matrix method. For the non-linear term
a spectral truncation method is used to remove aliasing errors. Combing the analytic and numerical solutions
the amplification mechanisms are revealed
and the influences of the parameters of electromagnetic forces and flow field are discussed. The results show that the amplification of velocity response along the streamwise direction is proportional to
Re
2
for small amplitude
i.e.
the responses in the linear stage. Moreover
the amplification of response increases firstly and then decreases with the increase of the effective penetration
Δ
while the amplification monotonically decreases with the increase of wave number along the spanwise direction. However
with the increase of amplitude
the response amplification approaches the nonlinear stage. The amplification monotonically decreases
while the amplitude value of velocity response increases firstly and then decreases. Moreover
the amplitude value reaches the maximum which is more than
0.2
and the corresponding amplification is the order of 10
2
. Therefore
the flow induced by the electromagnetic force is amplified with the effect of flow field
which is the key to enhance the efficiency of flow control.
关键词
Keywords
references
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