IPO windows tend to come and go. For the past eight months, that window has been wide open, allowing companies such as LinkedIn, Pandora and Zillow to start trading in the public markets. A whopping $26 billion flowed into IPOs during the first half of 2011, nearly triple the totals for the same period last year, according to data compiled by Tableau.

But the turmoil in the financial markets in recent days has sparked some worries — especially among venture capitalists — that the window may have just slammed shut.

Speaking at a panel discussion this week in Seattle, Madrona Venture Group’s Greg Gottesman said that he hopes that the window stays open. But the venture capitalist, whose firm backed Impinj, a Seattle RFID company that’s waiting to go public, isn’t sure what will happen.

Greg Gottesman

“If that closes again, like it was for a long time, then I think it is going to be a little more tough sledding,” said Gottesman.

“At some point, all of these things that are happening outside of the tech world will come and bite us, and it feels like there is a bear outside the log cabin and it is rustling around and you are waiting for it to rear its ugly head,” he said.

That bear hasn’t quite knocked the IPO market off its path, at least not yet. As seen in the data below, 2011 is shaping up to be one of the strongest periods for IPOs in years.

Here’s a look at the data compiled by Tableau from Renaissance Capital.

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