多孔介質指形流泛指一種流動介面的不穩定性現象，時常發生於低黏度流體驅替高黏度流體的過程。過去研究證實線性時變流率可以抑制徑向Hele-Shaw cell的注入流指形，然而對於吸出流指形與流體壁面間的濕潤性影響則尚無研究。本文使用徑向Hele-Shaw cell研究時變流率對低黏度流體推動高黏度流體的影響，並針對三個重要參數：毛細數、驅替時間及濕潤性進行探討。研究結果顯示對於注入實驗，非濕潤流體驅替濕潤流體的排移式較濕潤流體驅替非濕潤流體的浸潤式穩定許多，而於實驗考慮的不同之毛細數與驅替時間時變流率相較於固定流率皆具有抑制指形的效果。對於吸出實驗，只有毛細數較低的情況時變流率才具有抑制指形的效果，而驅替時間則會有一適當範圍可使得時變流率得到指形抑制效果與最少的待驅替流體殘留值；另外，濕潤性影響而產生的濕潤膜現象對吸出時變流率亦具有一定的影響力，可透過計算濕潤膜來修正時變流率以達到較佳的介面穩定效果。

Viscos fingering is a fluid interface instability phenomenon. It occurs when a less viscous fluid displaces another relatively more viscous fluid. For this problem, most researchers have used Hele-Shaw cells to study the fingering effects. Previous literature has shown that a linearly time-dependent injection flow rate can suppress viscous fingering in a drainage flow. However, it is not clear whether this is still true for other situations, like an imbibition displacement and extraction flow. In this study we used a radial Hele-Shaw cell, in which less viscous fluids were used to displace more viscous fluids to experimentally investigate how viscous fingering may evolve for different wettability with time-dependent flow rates. Effects of dimensionless final time, and capillary number were considered too. The results showed that the linearly time-dependent injection flow rate could more effectively suppress viscous fingering in drainage displacement than in imbibition displacement. No matter how capillary number, dimensionless final time and wettability change, the linear injection rate can still suppress the fingering instability. However, for the extraction case, the linearly time-dependent flow rate could not always suppress the fingering instability. The linearly time-dependent flow rate could suppress the fingering instability only for lower capillary numbers. For the dimensionless final time, there might exist an appropriate range, in which the linearly time-dependent flow rate suppress the fingering instability. For wettability effect, the wetting film impairs the suppression effect of the linearly time-dependent flow rate on viscous fingering. Based on the finding, the linearly time-dependent flow rate should be adjusted taken into account the wetting film.

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